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COMMISSIONING OF A DYNAMIC MECHANICAL ANALYZERFOR THE CHARACTERIZATION OF LOW TEMPERATURE NITIFE SHAPE MEMORY ALLOYS
Title
COMMISSIONING OF A DYNAMIC MECHANICAL ANALYZERFOR THE CHARACTERIZATION OF LOW TEMPERATURE NITIFE SHAPE MEMORY ALLOYS.
Creator
Nandiraju, Maruthi Diwakar, Vaidyanathan, Raj, University of Central Florida
Abstract / Description
NiTiFe shape memory alloys can undergo transformations between cubic, trigonal and monoclinic phases at low temperatures. The low hysteresis associated with the trigonal R-phase transformation make them candidates for actuator applications at low temperatures. However, the literature available on these alloys is limited and there is a need to establish processing-structure-property correlations. This study was undertaken with the objective of determining and understanding such correlations in...
Show moreNiTiFe shape memory alloys can undergo transformations between cubic, trigonal and monoclinic phases at low temperatures. The low hysteresis associated with the trigonal R-phase transformation make them candidates for actuator applications at low temperatures. However, the literature available on these alloys is limited and there is a need to establish processing-structure-property correlations. This study was undertaken with the objective of determining and understanding such correlations in a Ni46.8Ti50Fe3.2 alloy. First, a dynamic mechanical analyzer (DMA) was successfully commissioned to facilitate mechanical testing between -150 and 600ºC. The experiments performed over selected ranges of stress and temperature probed a range of deformation phenomena in these materials. In addition to conventional elastic and dislocation based plastic deformation, also probed were stress-induced formation of the R- and martensite (B19') phases, and twinning in the R- and martensite (B19') phases. Constrained recovery experiments, wherein phase transformations were thermally induced against external loads, were also performed to assess the performance of these alloys in actuator applications. In addition to a DMA, a differential scanning calorimeter, liquid helium dilatometer and a transmission electron microscope were also used. The samples tested were subjected to different thermo-mechanical processing parameters (i.e., percentage of cold work, solutionizing, aging, and annealing time/temperature). Selected combinations of cold work and annealing temperature/times were found to result in narrower transformations (in temperature space), making such alloys of value in cyclic actuator applications. Thus this work contributed to further understand the processing-structure-property relationship in NiTiFe alloys that exhibit the R-phase transformation and in lowering the operating temperature range of shape-memory alloys in order for them to be used in hydrogen related technologies. The immediate benefit to NASA Kennedy Space Center is the development of a shape-memory thermal conduction switch for application in cryogenic liquefaction, densification and zero boil-off systems. This is being extended to include the potential use of shape-memory alloy actuator elements for cryogenic seals, valves, fluid-line repair, self-healing gaskets, and even to ambient debris-less separation and latch/release mechanisms. The financial support of NASA through grant NAG3-2751 is gratefully acknowledged.
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Date Issued
2006
Identifier
CFE0001409, ucf:47041
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0001409
A METHODOLOGY FOR INSTRUMENTED INDENTATION STUDIES OF DEFORMATION IN BULK METALLIC GLASSES
Title
A METHODOLOGY FOR INSTRUMENTED INDENTATION STUDIES OF DEFORMATION IN BULK METALLIC GLASSES.
Creator
Sridharan, Subhaashree, Vaidyanathan, Raj, University of Central Florida
Abstract / Description
Bulk Metallic Glasses (BMGs), also known as amorphous metals, are of considerable scientific and commercial interest due to their random or chaotic structure. Given their potential use as engineering materials, there is a concomitant need to establish their mechanical properties. However, BMGs are not conveniently available in sufficient volumes (especially experimental and combinatorial compositions), making property determination via conventional tensile or compression testing problematic....
Show moreBulk Metallic Glasses (BMGs), also known as amorphous metals, are of considerable scientific and commercial interest due to their random or chaotic structure. Given their potential use as engineering materials, there is a concomitant need to establish their mechanical properties. However, BMGs are not conveniently available in sufficient volumes (especially experimental and combinatorial compositions), making property determination via conventional tensile or compression testing problematic. Instrumented indentation is ideally suited for this purpose because the testing requires only small sampling volumes and can probe multiaxial deformation characteristics at various length scales. In this technique, conducted generally on a sub-micron regime, the depth of penetration of an indenter, usually a diamond, is measured as a function of the applied load and expressed graphically as load (P) - displacement (h) curves from which a host of mechanical properties can be extracted and studied. In this work, a methodology for using instrumented indentation at nano- and micro- scales to determine the mechanical response of BMGs was developed and implemented. The implementation primarily focused on deformation in the elastic regime but included preliminary results related to the onset of inelastic deformation. The methodology developed included calibration techniques, formulations to extract the machine compliances, verifications using standards and verification for uniqueness of instrument deformation under a spherical indenter. The methodology was different for the two platforms used based on the load-depth response characteristics of the instrument. In the case of the Micro Test platform, the load-depth response of the instrument was linear. In the case of the Nano Test platform, the instrument load-depth response followed a 3/2 power law, representative of Hertzian behavior. The load-depth response of the instrument was determined by subtracting the theoretical response from the corresponding raw load-depth response obtained by elastically indenting a standard steel specimen of known modulus. The true response of the sample was then obtained by subtracting the instrument's response from the corresponding uncorrected load-depth response (raw data). An analytical model to describe the load-train compliance was developed. The methodology was verified using quartz and tungsten standards. Indentation experiments were conducted on Zr41.25Ti13.75Cu12.5Ni10Be22.5 (Vitreloy 1), Cu60Hf25Ti15, Cu60Zr30Ti10 and Fe60Co7Zr10Mo5W2B16 bulk metallic glasses using spherical indenters with diameters 2.8 mm and 100 m. The spherical geometry results in a simpler stress distribution under the indenter (when compared to a sharp geometry) and furthermore by recourse to spherical indenters the onset of plastic deformation was delayed. In the case of the Zr-based BMG, the experiments showed that the elastic response did not depend on the diameter of the indenter used indicative of the absence of residual stresses in the sample. Large scale plastic deformation was observed when the sample was indented using a smaller diameter indenter. Log scale analysis (i.e., examining the results on a log load vs. log depth response to check for deviation from Hertzian behavior) showed a deviation from a 3/2 fit indicating a deviation from elastic behavior. The onset implied a yield strength value of ~ 4 GPa, higher than the value reported in the literature (~ 2 GPa). Hence, it is believed that the first signs of plastic deformation occurred at lower loads than the predicted loads from the log scale analysis procedure and is expected to occur as discrete bursts. Discrete plastic events or "pop-ins" were observed in the load-depth indentation responses under quasistatic loading conditions, which were believed to be associated with shear band activity. An attempt was made to formulate a mathematical model based on three yield criteria (Drucker-Prager, Mohr-Coulomb and von Mises). Based on the von Mises predictions and comparable experiments on a quartz standard, it was established that the pop-ins observed were real and not an instrument artifact. Multiple load cycles following partial unload experiments showed that the pop-ins affected the subsequent indentation response. The moduli and the yield strength values obtained for the Cu-based BMGs were comparable to the values reported in the literature. There was significant scatter in the indentation data from the Fe-based BMG. Porosity and lack of 100 % compaction were believed to be the reasons for scatter in the data. The financial support of NSF through grant DMR 0314212 is gratefully acknowledged.
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Date Issued
2006
Identifier
CFE0001442, ucf:47047
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0001442
COMMISSIONING OF AN ARC-MELTING / VACUUM QUENCH FURNACE FACILITY FOR FABRICATION OF NI-TI-FE SHAPE MEMORY ALLOYS, AND THEIR CHARACTERIZATION
Title
COMMISSIONING OF AN ARC-MELTING / VACUUM QUENCH FURNACE FACILITY FOR FABRICATION OF NI-TI-FE SHAPE MEMORY ALLOYS, AND THEIR CHARACTERIZATION.
Creator
Singh, Jagat, Vaidyanathan, Raj, University of Central Florida
Abstract / Description
Shape memory alloys when deformed can produce strains as high as 8%. Heating results in a phase transformation and associated recovery of all the accumulated strain, a phenomenon known as shape memory. This strain recovery can occur against large forces, resulting in their use as actuators. The goal of this project is to lower the operating temperature range of shape memory alloys in order for them to be used in cryogenic switches, seals, valves, fluid-line repair and self-healing gaskets for...
Show moreShape memory alloys when deformed can produce strains as high as 8%. Heating results in a phase transformation and associated recovery of all the accumulated strain, a phenomenon known as shape memory. This strain recovery can occur against large forces, resulting in their use as actuators. The goal of this project is to lower the operating temperature range of shape memory alloys in order for them to be used in cryogenic switches, seals, valves, fluid-line repair and self-healing gaskets for space related technologies. The Ni-Ti-Fe alloy system, previously used in Grumman F-14 aircrafts and activated at 120 K, is further developed through arc-melting a range of compositions and subsequent thermo-mechanical processing. A controlled atmosphere arc-melting facility and vertical vacuum quench furnace facility was commissioned to fabricate these alloys. The facility can create a vacuum of 10-7 Torr and heat treat samples up to 977 °C. High purity powders of Ni, Ti and Fe in varying ratios were mixed and arc-melted into small buttons weighing 0.010 kg to 0.025 kg. The alloys were subjected to solutionizing and aging treatments. A combination of rolling, electro-discharge machining and low-speed cutting techniques were used to produce strips. Successful rolling experiments highlighted the workability of these alloys. The shape memory effect was successfully demonstrated at liquid nitrogen temperatures through a constrained recovery experiment that generated stresses of over 40 MPa. Differential scanning calorimetry (DSC) and a dilatometry setup was used to characterize the fabricated materials and determine relationships between composition, thermo-mechanical processing parameters and transformation temperatures.
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Date Issued
2004
Identifier
CFE0000308, ucf:46320
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000308
LOW TEMPERATURE NITIFE SHAPE MEMORY ALLOYS: ACTUATOR ENGINEERING AND INVESTIGATION OF DEFORMATION MECHANISMS USING IN SITU NEUTRON DIFFRACTION AT LOS ALAMOS NATIONAL LABORATORY
Title
LOW TEMPERATURE NITIFE SHAPE MEMORY ALLOYS: ACTUATOR ENGINEERING AND INVESTIGATION OF DEFORMATION MECHANISMS USING IN SITU NEUTRON DIFFRACTION AT LOS ALAMOS NATIONAL LABORATORY.
Creator
Krishnan, Vinu, Vaidyanathan, Raj, University of Central Florida
Abstract / Description
Shape memory alloys are incorporated as actuator elements due to their inherent ability to sense a change in temperature and actuate against external loads by undergoing a shape change as a result of a temperature-induced phase transformation. The cubic so-called austenite to the trigonal so-called R-phase transformation in NiTiFe shape memory alloys offers a practical temperature range for actuator operation at low temperatures, as it exhibits a narrow temperature-hysteresis with a desirable...
Show moreShape memory alloys are incorporated as actuator elements due to their inherent ability to sense a change in temperature and actuate against external loads by undergoing a shape change as a result of a temperature-induced phase transformation. The cubic so-called austenite to the trigonal so-called R-phase transformation in NiTiFe shape memory alloys offers a practical temperature range for actuator operation at low temperatures, as it exhibits a narrow temperature-hysteresis with a desirable fatigue response. Overall, this work is an investigation of selected science and engineering aspects of low temperature NiTiFe shape memory alloys. The scientific study was performed using in situ neutron diffraction measurements at the newly developed low temperature loading capability on the Spectrometer for Materials Research at Temperature and Stress (SMARTS) at Los Alamos National Laboratory and encompasses three aspects of the behavior of Ni46.8Ti50Fe3.2 at 92 K (the lowest steady state temperature attainable with the capability). First, in order to study deformation mechanisms in the R-phase in NiTiFe, measurements were performed at a constant temperature of 92 K under external loading. Second, with the objective of examining NiTiFe in one-time, high-stroke, actuator applications (such as in safety valves), a NiTiFe sample was strained to approximately 5% (the R-phase was transformed to B19' phase in the process) at 92 K and subsequently heated to full strain recovery under a load. Third, with the objective of examining NiTiFe in cyclic, low-stroke, actuator applications (such as in cryogenic thermal switches), a NiTiFe sample was strained to 1% at 92 K and subsequently heated to full strain recovery under load. Neutron diffraction spectra were recorded at selected time and stress intervals during these experiments. The spectra were subsequently used to obtain quantitative information related to the phase-specific strain, texture and phase fraction evolution using the Rietveld technique. The mechanical characterization of NiTiFe alloys using the cryogenic capability at SMARTS provided considerable insight into the mechanisms of phase transformation and twinning at cryogenic temperatures. Both mechanisms contribute to shape memory and pseudoelasticity phenomena. Three phases (R, B19' and B33 phases) were found to coexist at 92 K in the unloaded condition (nominal holding stress of 8 MPa). For the first time the elastic modulus of R-phase was reported from neutron diffraction experiments. Furthermore, for the first time a base-centered orthorhombic (B33) martensitic phase was identified experimentally in a NiTi-based shape memory alloy. The orthorhombic B33 phase has been theoretically predicted in NiTi from density function theory (DFT) calculations but hitherto has never been observed experimentally. The orthorhombic B33 phase was observed while observing shifting of a peak (identified to be B33) between the R and B19' peaks in the diffraction spectra collected during loading. Given the existing ambiguity in the published literature as to whether the trigonal R-phase belongs to the P3 or P space groups, Rietveld analyses were separately carried out incorporating the symmetries associated with both space groups and the impact of this choice evaluated. The constrained recovery of the B19' phase to the R-phase recorded approximately 4% strain recovery between 150 K and 170 K, with half of that recovery occurring between 160 K and 162 K. Additionally, the aforementioned research methodology developed for Ni46.8Ti50Fe3.2 shape memory alloys was applied to experiments performed on a new high temperature Ni29.5Ti50.5Pd20 shape memory alloys. The engineering aspect focused on the development of (i) a NiTiFe based thermal conduction switch that minimized the heat gradient across the shape memory actuator element, (ii) a NiTiFe based thermal conduction switch that incorporated the actuator element in the form of helical springs, and (iii) a NiTi based release mechanism. Patents are being filed for all the three shape memory actuators developed as a part of this work. This work was supported by grants from SRI, NASA (NAG3-2751) and NSF (CAREER DMR-0239512) to UCF. Additionally, this work benefited from the use of the Lujan Center at the Los Alamos Neutron Science Center, funded by the United States Department of Energy, Office of Basic Energy Sciences, under Contract No. W-7405-ENG-36.
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Date Issued
2007
Identifier
CFE0001934, ucf:47437
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0001934
TRANSMISSION ELECTRON MICROSCOPY STUDIES IN SHAPE MEMORY ALLOYS
Title
TRANSMISSION ELECTRON MICROSCOPY STUDIES IN SHAPE MEMORY ALLOYS.
Creator
TIYYAGURA, MADHAVI, VAIDYANATHAN, RAJ, University of Central Florida
Abstract / Description
In NiTi, a reversible thermoelastic martensitic transformation can be induced by temperature or stress between a cubic (B2) austenite phase and a monoclinic (B19') martensite phase. Ni-rich binary compositions are cubic at room temperature (requiring stress or cooling to transform to the monoclinic phase), while Ti-rich binary compositions are monoclinic at room temperature (requiring heating to transform to the cubic phase). The stress induced transformation results in the superelastic...
Show moreIn NiTi, a reversible thermoelastic martensitic transformation can be induced by temperature or stress between a cubic (B2) austenite phase and a monoclinic (B19') martensite phase. Ni-rich binary compositions are cubic at room temperature (requiring stress or cooling to transform to the monoclinic phase), while Ti-rich binary compositions are monoclinic at room temperature (requiring heating to transform to the cubic phase). The stress induced transformation results in the superelastic effect, while the thermally induced transformation is associated with strain recovery that results in the shape memory effect. Ternary elemental additions such as Fe can additionally introduce an intermediate rhombohedral (R) phase between the cubic and monoclinic phase transformation. This work was initiated with the broad objective of connecting the macroscopic behavior in shape memory alloys with microstructural observations from transmission electron microscopy (TEM). Specifically, the goals were to examine (i) the effect of mechanical cycling and plastic deformation in superelastic NiTi; (ii) the effect of thermal cycling during loading in shape memory NiTi; (iii) the distribution of twins in martensitic NiTi-TiC composites; and (iv) the R-phase in NiTiFe. Both in situ and ex situ lift out focused ion beam (FIB) and electropolishing techniques were employed to fabricate shape memory alloy samples for TEM characterization. The Ni rich NiTi samples were fully austenitic in the undeformed state. The introduction of plastic deformation (8% and 14% in the samples investigated) resulted in the stabilization of martensite in the unloaded state. An interlaying morphology of the austenite and martensite was observed and the martensite needles tended to orient themselves in preferred orientations. The aforementioned observations were more noticeable in mechanically cycled samples. The observed dislocations in mechanically cycled samples appear to be shielded from the external applied stress via mismatch accommodation since they are not associated with unrecoverable strain after a load-unload cycle. On application of stress, the austenite transforms to martensite and is expected to accommodate the stress and strain mismatch through preferential transformation, variant selection, reorientation and coalescence. The stabilized martensite (i.e., martensite that exists in the unloaded state) is expected to accommodate the mismatch through variant reorientation and coalescence. On thermally cycling a martensitic NiTi sample under load through the phase transformation, significant variant coalescence, variant reorientation and preferred variant selection was observed. This was attributed to the internal stresses generated as a result of the thermal cycling. A martensitic NiTi-TiC composite was also characterized and the interface between the matrix and the inclusion was free of twins while significant twins were observed at a distance away from the matrix-inclusion interface. Incorporating a cold stage, diffraction patterns from NiTiFe samples were obtained at temperatures as low as -160ºC. Overall, this work provided insight in to deformation phenomena in shape memory materials that have implications for engineering applications (e.g., cyclic performance of actuators, engineering life of superelastic components, stiffer shape memory composites and low-hysteresis R-phase based actuators). This work was supported in part by an NSF CAREER award (DMR 0239512).
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Date Issued
2005
Identifier
CFE0000500, ucf:46462
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000500
DESIGN, FABRICATION AND TESTING OF A SHAPE MEMORY ALLOY BASED CRYOGENIC THERMAL CONDUCTION SWITCH
Title
DESIGN, FABRICATION AND TESTING OF A SHAPE MEMORY ALLOY BASED CRYOGENIC THERMAL CONDUCTION SWITCH.
Creator
Krishnan, Vinu Bala, Vaidyanathan, Raj, University of Central Florida
Abstract / Description
Shape memory alloys (SMAs) can recover large strains (e.g., up to 8%) by undergoing a temperature-induced phase transformation. This strain recovery can occur against large forces, resulting in their use as actuators. The SMA elements in such actuators integrate both sensory and actuation functions. This is possible because SMAs can inherently sense a change in temperature and actuate by undergoing a shape change, associated with the temperature-induced phase transformation. The objective of...
Show moreShape memory alloys (SMAs) can recover large strains (e.g., up to 8%) by undergoing a temperature-induced phase transformation. This strain recovery can occur against large forces, resulting in their use as actuators. The SMA elements in such actuators integrate both sensory and actuation functions. This is possible because SMAs can inherently sense a change in temperature and actuate by undergoing a shape change, associated with the temperature-induced phase transformation. The objective of this work is to develop an SMA based cryogenic thermal conduction switch for operation between dewars of liquid methane and liquid oxygen in a common bulk head arrangement for NASA. The design of the thermal conduction switch is based on a biased, two-way SMA actuator and utilizes a commercially available NiTi alloy as the SMA element to demonstrate the feasibility of this concept. This work describes the design from concept to implementation, addressing methodologies and issues encountered, including: a finite element based thermal analysis, various thermo-mechanical processes carried out on the NiTi SMA elements, and fabrication and testing of a prototype switch. Furthermore, recommendations for improvements and extension to NASA's requirements are presented. Such a switch has potential application in variable thermal sinks to other cryogenic tanks for liquefaction, densification, and zero boil-off systems for advanced spaceport applications. The SMA thermal conduction switch offers the following advantages over the currently used gas gap and liquid gap thermal switches in the cryogenic range: (i) integrates both sensor and actuator elements thereby reducing the overall complexity, (ii) exhibits superior thermal isolation in the open state, and (iii) possesses high heat transfer ratios between the open and closed states. This work was supported by a grant from NASA Kennedy Space Center (NAG10-323) with William U. Notardonato as Technical Officer.
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Date Issued
2004
Identifier
CFE0000038, ucf:46136
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000038
DIFFRACTION STUDIES OF DEFORMATION IN SHAPE MEMORY ALLOYS AND SELECTED ENGINEERING COMPONENTS
Title
DIFFRACTION STUDIES OF DEFORMATION IN SHAPE MEMORY ALLOYS AND SELECTED ENGINEERING COMPONENTS.
Creator
RATHOD, CHANDRASEN, Vaidyanathan, Raj, University of Central Florida
Abstract / Description
Deformation phenomena in shape memory alloys involve stress-, temperature-induced phase transformations and crystallographic variant conversion or reorientation, equivalent to a twinning operation. In near equiatomic NiTi, Ti rich compositions can exist near room temperature as a monoclinic B19' martensitic phase, which when deformed undergoes twinning resulting in strains as large as 8%. Upon heating, the martensite transforms to a cubic B2 austenitic phase, thereby recovering the strain and...
Show moreDeformation phenomena in shape memory alloys involve stress-, temperature-induced phase transformations and crystallographic variant conversion or reorientation, equivalent to a twinning operation. In near equiatomic NiTi, Ti rich compositions can exist near room temperature as a monoclinic B19' martensitic phase, which when deformed undergoes twinning resulting in strains as large as 8%. Upon heating, the martensite transforms to a cubic B2 austenitic phase, thereby recovering the strain and exhibiting the shape memory effect. Ni rich compositions on the other hand can exist near room temperature in the austenitic phase and undergo a reversible martensitic transformation on application of stress. Associated with this reversible martensitic transformation are macroscopic strains, again as large as 8%, which are also recovered and resulting in superelasticity. This work primarily focuses on neutron diffraction measurements during loading at the Los Alamos Neutron Science Center at Los Alamos National Laboratory. Three phenomena were investigated: First, the phenomena of hysteresis reduction and increase in linearity with increasing plastic deformation in superelastic NiTi. There is usually a hysteresis associated with the forward and reverse transformations in superelastic NiTi which translates to a hysteresis in the stress-strain curve during loading and unloading. This hysteresis is reduced in cold-worked NiTi and the macroscopic stress-strain response is more linear. This work reports on measurements during loading and unloading in plastically deformed (up to 11%) and cycled NiTi. Second, the tension-compression stress-strain asymmetry in martensitic NiTi. This work reports on measurements during tensile and compressive loading of polycrystalline shape-memory martensitic NiTi with no starting texture. Third, a heterogeneous stress-induced phase transformation in superelastic NiTi. Measurements were performed on a NiTi disc specimen loaded laterally in compression and associated with a macroscopically heterogeneous stress state. For the case of superelastic NiTi, the experiments related the macroscopic stress-strain behavior (from an extensometer or an analytical approach) with the texture, phase volume fraction and strain evolution (from neutron diffraction spectra). For the case of shape memory NiTi, the macroscopic connection was made with the texture and strain evolution due to twinning and elastic deformation in martensitic NiTi. In all cases, this work provided for the first time insight into atomic-scale phenomena such as mismatch accommodation and martensite variant selection. The aforementioned technique of neutron diffraction for mechanical characterization was also extended to engineering components and focused mainly on the determination of residual strains. Two samples were investigated and presented in this work; first, a welded INCONEL 718 NASA space shuttle flow liner was studied at 135 K and second, Ti-6Al-4V turbine blade components were investigated for Siemens Westinghouse Power Corporation. Lastly, also reported in this dissertation is a refinement of the methodology established in the author's masters thesis at UCF that used synchrotron x-ray diffraction during loading to study superelastic NiTi. The Los Alamos Neutron Science Center is a national user facility funded by the United States Department of Energy, Office of Basic Energy Sciences, under Contract No. W-7405-ENG-36. The work reported here was made possible by grants to UCF from NASA (NAG3-2751), NSF CAREER (DMR-0239512), Siemens Westinghouse Power Corporation and the Space Research Initiative.
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Date Issued
2005
Identifier
CFE0000723, ucf:46608
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000723
LOW TEMPERATURE AND REDUCED LENGTH SCALE BEHAVIOR OF SHAPE MEMORY AND SUPERELASTIC NITI AND NITIFE ALLOYS
Title
LOW TEMPERATURE AND REDUCED LENGTH SCALE BEHAVIOR OF SHAPE MEMORY AND SUPERELASTIC NITI AND NITIFE ALLOYS.
Creator
Manjeri, Radhakrishnan, Vaidyanathan, Raj, University of Central Florida
Abstract / Description
Shape memory and superelastic applications of NiTi based alloys have typically been limited to near room temperature or to bulk length scales. The objective of this work is two-fold: first, to investigate shape memory behavior at low temperatures in the context of the R-phase transformation in NiTiFe alloys by recourse to arc-melting, differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and mechanical testing at low temperatures; and second, to investigate...
Show moreShape memory and superelastic applications of NiTi based alloys have typically been limited to near room temperature or to bulk length scales. The objective of this work is two-fold: first, to investigate shape memory behavior at low temperatures in the context of the R-phase transformation in NiTiFe alloys by recourse to arc-melting, differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and mechanical testing at low temperatures; and second, to investigate superelasticity and two-way shape memory behavior at reduced length scales in the context of NiTi by recourse to micro-compression, micro-indentation and TEM studies. Selected compositions of ternary NiTiFe shape memory alloys were arc-melted and thermo-mechanically processed to investigate the influence of composition and processing parameters on the formation of the R-phase. The methodology used for the processing and characterization of the alloys was established and included microprobe analysis, DSC, TEM and mechanical testing. No phase transformation was observed in alloys with Fe content in excess of 4 at.%. Thermo-mechanical treatments facilitated the formation of the R-phase in Ni-rich alloys. The range of the transformation between the R-phase and austenite, and the hysteresis associated with it were influenced by the distribution and size of metastable Ni4Ti3 precipitates. The investigation of the microstructural, thermal and mechanical properties of the R-phase transformation in NiTiFe alloys revealed a complex dependence of these properties on processing parameters. The present work also highlighted the hitherto unexplored competition between the two inelastic deformation modes operating in the R-phase (detwinning and stress-induced transformation) and established the preference of one mode over the other in stress-temperature space. The complete micromechanical response of superelastic NiTi was examined by performing careful micro-compression experiments on single crystal pillars of known orientations using a nanoindenter tip. Specifically, the orientation dependence of the elastic deformation of austenite, the onset of its transformation to martensite, the gradient and the hysteresis in the stress-strain response during transformation, the elastic modulus of the stress-induced martensite and the onset of plasticity of the stress-induced martensite were analyzed in separate experiments. A majority of the results were explained by recourse to a quantitative determination of strains associated with austenite grains transforming to martensite variants or twinning in martensite. Microstructural studies were also performed on a micro-indentation trained NiTi shape memory alloy specimen to understand the mechanisms governing the two-way shape memory effect. In situ TEM studies at temperature on specimens obtained at different depths below the indent showed the presence of retained martensite along with the R-phase. Previously, while such two-way shape memory behavior has typically been associated with large dislocation densities, this work provides evidence of the role of retained martensite and the R-phase in cases with reduced dislocation densities. Funding support for this work from NSF (CAREER DMR-0239512), NASA (NAG3-2751) and SRI is acknowledged.
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Date Issued
2009
Identifier
CFE0002825, ucf:48065
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0002825
INVESTIGATION OF THERMAL, ELASTIC AND LOAD-BIASED TRANSFORMATION STRAINS IN NITI SHAPE MEMORY ALLOYS
Title
INVESTIGATION OF THERMAL, ELASTIC AND LOAD-BIASED TRANSFORMATION STRAINS IN NITI SHAPE MEMORY ALLOYS.
Creator
Qiu, Shipeng, Vaidyanathan, Raj, University of Central Florida
Abstract / Description
Polycrystalline NiTi shape memory alloys have the ability to recover their original, pre-deformed shape in the presence of external loads when heated through a solid-solid phase transformation from a lower-symmetry B19' martensite phase to a higher-symmetry B2 austenite phase. The strain associated with a shape memory alloy in an actuator application typically has thermal, elastic and inelastic contributions. The objective of this work was to investigate the aforementioned strains by...
Show morePolycrystalline NiTi shape memory alloys have the ability to recover their original, pre-deformed shape in the presence of external loads when heated through a solid-solid phase transformation from a lower-symmetry B19' martensite phase to a higher-symmetry B2 austenite phase. The strain associated with a shape memory alloy in an actuator application typically has thermal, elastic and inelastic contributions. The objective of this work was to investigate the aforementioned strains by recourse to in situ neutron diffraction experiments during selected combinations of heating, cooling and/or mechanical loading. The primary studies were conducted on polycrystalline Ni49.9Ti50.1 specimens on the Spectrometer for MAterials Research at Temperature and Stress (SMARTS) at Los Alamos National Laboratory. Quantitative information on the phase-specific strain, texture and phase fraction evolution was obtained from the neutron data using Rietveld refinement and single-peak analyses, and compared with macroscopic data from extensometry. First, the lattice strain evolution during heating and cooling in an unloaded sample (i.e., free-recovery experiment) was studied. The lattice strain evolution remained linear with temperature and was not influenced by intergranular stresses, enabling the determination of a thermal expansion tensor that quantified the associated anisotropy due to the symmetry of B19' NiTi. The tensor thus determined was subsequently used to obtain an average coefficient of thermal expansion that was consistent with macroscopic dilatometric measurements and a 30,000 grain polycrystalline self-consistent model. The accommodative nature of B19' NiTi was found to account for macroscopic shape changes lagging (with temperature) the start and finish of the transformation. Second, the elastic response of B19' martensitic NiTi variants during monotonic loading was studied. Emphasis was placed on capturing and quantifying the strain anisotropy which arises from the symmetry of monoclinic martensite and internal stresses resulting from intergranular constraints between individual variants and load re-distribution among variants as the texture evolved during variant reorientation and detwinning. The methodology adopted took into account both tensile and compressive loading given the asymmetric response in the texture evolution. Plane specific elastic moduli were determined from neutron measurements and compared with those determined using a self-consistent polycrystalline deformation model and from recently reported elastic stiffness constants determined via ab initio calculations. The comparison among the three approaches further helped understand the influence of elastic anisotropy, intergranular constraint, and texture evolution on the deformation behavior of polycrystalline B19' NiTi. Connections were additionally made between the assessed elastic properties of martensitic NiTi single crystals (i.e., the single crystal stiffness tensor) and the overall macroscopic response in bulk polycrystalline form. Lastly, the role of upper-cycle temperature, i.e., the maximum temperature reached during thermal cycling, was investigated during load-biased thermal cycling of NiTi shape memory alloys at selected combinations of stress and temperature. Results showed that the upper-cycle temperature, under isobaric conditions, significantly affected the amount of transformation strain and thus the work output available for actuation. With the objective of investigating the underlying microstructural and micromechanical changes due to the influence of the upper-cycle temperature, the texture evolution was systematically analyzed. While the changes in transformation strain were closely related to the evolution in texture of the room temperature martensite, retained martensite in the austenite state could additionally affect the transformation strain. Additionally, multiple thermal cycles were performed under load-biased conditions in both NiTi and NiTiPd alloys, to further assess and understand the role of retained martensite. Dimensional and thermal stabilities of these alloys were correlated with the volume fraction and texture of retained martensite, and the internal strain evolution in these alloys. The role of symmetry, i.e., B19' monoclinic martensite vs. B19 orthorhombic martensite in these alloys was also assessed. This work not only established a methodology to study the thermal and elastic properties of the low symmetry B19' monoclinic martensite, but also provided valuable insight into quantitative micromechanical and microstructural changes responsible for the thermomechanical response of NiTi shape memory alloys. It has immediate implications for optimizing shape memory behavior in the alloys investigated, with extension to high temperature shape memory alloys with ternary and quaternary elemental additions, such as Pd, Pt and Hf. This work was supported by funding from NASAÂÂ's Fundamental Aeronautics Program, Supersonics Project (NNX08AB51A) and NSF (CAREER DMR-0239512). It benefited additionally from the use of the Lujan Neutron Scattering Center at Los Alamos National Laboratory, which is funded by the Office of Basic Energy Sciences (Department of Energy) and is operated by Los Alamos National Security LLC under DOE Contract DE-AC52-06NA25396.
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Date Issued
2010
Identifier
CFE0003362, ucf:48440
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0003362
DESIGN, FABRICATION AND TESTING OF A LOW TEMPERATURE HEAT PIPE THERMAL SWITCH WITH SHAPE MEMORY HELICAL ACTUATORS
Title
DESIGN, FABRICATION AND TESTING OF A LOW TEMPERATURE HEAT PIPE THERMAL SWITCH WITH SHAPE MEMORY HELICAL ACTUATORS.
Creator
Benafan, Othmane, Vaidyanathan, Raj, University of Central Florida
Abstract / Description
This work reports on the design, fabrication and testing of a thermal switch wherein the open and closed states are actuated by shape memory alloy elements while heat is transferred by a heat-pipe. The motivation for such a switch comes from NASA's need for thermal management in advanced spaceport applications associated with future lunar and Mars missions. For example, as the temperature can approximately vary between 40 K to 400 K during lunar day/night cycles, such a switch can reject...
Show moreThis work reports on the design, fabrication and testing of a thermal switch wherein the open and closed states are actuated by shape memory alloy elements while heat is transferred by a heat-pipe. The motivation for such a switch comes from NASA's need for thermal management in advanced spaceport applications associated with future lunar and Mars missions. For example, as the temperature can approximately vary between 40 K to 400 K during lunar day/night cycles, such a switch can reject heat from a cryogen tank in to space during the night cycle while providing thermal isolation during the day cycle. By utilizing shape memory alloy elements in the thermal switch, the need for complicated sensors and active control systems are eliminated while offering superior thermal isolation in the open state. Nickel-Titanium-Iron (Ni-Ti-Fe) shape memory springs are used as the sensing and actuating elements. Iron (Fe) lowers the phase transformation temperatures to cryogenic regimes of operation while introducing an intermediate, low hysteretic, trigonal R-phase in addition to the usual cubic and monoclinic phases typically observed in binary NiTi. The R-phase to cubic phase transformation is used in this application. The methodology of shape memory spring design and fabrication from wire including shape setting is described. Heat transfer is accomplished via heat acquisition, transport and rejection in a variable length heat pipe with pentane and R-134a as working fluids. The approach used to design the shape memory elements, quantify the heat transfer at both ends of the heat pipe and the pressures and stresses associated with the actuation are outlined. Testing of the switch is accomplished in a vacuum bell jar with instrumentation feedthroughs using valves to control the flow of liquid nitrogen and heaters to simulate the temperature changes. Various performance parameters are measured and reported under both transient and steady-state conditions. Funding from NASA Kennedy Space Center for this work is gratefully acknowledged.
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Date Issued
2009
Identifier
CFE0002810, ucf:48142
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0002810
INVESTIGATION OF PS-PVD AND EB-PVD THERMAL BARRIER COATINGS OVER LIFETIME USING SYNCHROTRON X-RAY DIFFRACTION
Title
INVESTIGATION OF PS-PVD AND EB-PVD THERMAL BARRIER COATINGS OVER LIFETIME USING SYNCHROTRON X-RAY DIFFRACTION.
Creator
Northam, Matthew, Raghavan, Seetha, Ghosh, Ranajay, Vaidyanathan, Raj, University of Central Florida
Abstract / Description
Extreme operating temperatures within the turbine section of jet engines require sophisticated methods of cooling and material protection. Thermal barrier coatings (TBCs) achieve this through a ceramic coating applied to a substrate material (nickel-based superalloy). Electron-beam physical vapor deposition (EB-PVD) is the industry standard coating used on jet engines. By tailoring the microstructure of an emerging deposition method, Plasma-spray physical vapor deposition (PS-PVD), similar...
Show moreExtreme operating temperatures within the turbine section of jet engines require sophisticated methods of cooling and material protection. Thermal barrier coatings (TBCs) achieve this through a ceramic coating applied to a substrate material (nickel-based superalloy). Electron-beam physical vapor deposition (EB-PVD) is the industry standard coating used on jet engines. By tailoring the microstructure of an emerging deposition method, Plasma-spray physical vapor deposition (PS-PVD), similar microstructures to that of EB-PVD coatings can be fabricated, allowing the benefits of strain tolerance to be obtained while improving coating deposition times. This work investigates the strain through depth of uncycled and cycled samples using these coating techniques with synchrotron X-ray diffraction (XRD). In the TGO, room temperature XRD measurements indicated samples of both deposition methods showed similar in-plane compressive stresses after 300 and 600 thermal cycles. In-situ XRD measurements indicated similar high-temperature in-plane and out-of-plane stress in the TGO and no spallation after 600 thermal cycles for both coatings. Tensile in-plane residual stresses were found in the YSZ uncycled PS-PVD samples, similar to APS coatings. PS-PVD samples showed in most cases, higher compressive residual in-plane stress at the YSZ/TGO interface. These results provide valuable insight for optimizing the PS-PVD processing parameters to obtain strain compliance similar to that of EB-PVD. Additionally, external cooling methods used for thermal management in jet engine turbines were investigated. In this work, an additively manufactured lattice structure providing transpiration cooling holes is designed and residual strains are measured within an AM transpiration cooling sample using XRD. Strains within the lattice structure were found to have greater variation than that of the AM solid wall. These results provide valuable insight into the viability of implementing an AM lattice structure in turbine blades for the use of transpiration cooling.
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Date Issued
2019
Identifier
CFE0007844, ucf:52830
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007844
Analysis of residual stress and damage mechanisms of thermal barrier coatings deposited via PS-PVD and EB-PVD
Title
Analysis of residual stress and damage mechanisms of thermal barrier coatings deposited via PS-PVD and EB-PVD.
Creator
Rossmann, Linda, Raghavan, Seetha, Sohn, Yongho, Vaidyanathan, Raj, Ghosh, Ranajay, University of Central Florida
Abstract / Description
Thermal barrier coatings (TBCs) are critical to gas turbine engines, as they protect the components in the hot section from the extreme temperatures of operation. The current industry standard method of applying TBCs for turbine blades in jet engines is electron-beam physical vapor deposition (EB-PVD), which results in a columnar structure that is valued for its high degree of strain tolerance. An emerging deposition method is plasma-spray physical vapor deposition (PS-PVD), capable of...
Show moreThermal barrier coatings (TBCs) are critical to gas turbine engines, as they protect the components in the hot section from the extreme temperatures of operation. The current industry standard method of applying TBCs for turbine blades in jet engines is electron-beam physical vapor deposition (EB-PVD), which results in a columnar structure that is valued for its high degree of strain tolerance. An emerging deposition method is plasma-spray physical vapor deposition (PS-PVD), capable of producing a variety of customizable microstructures as well as non-line-of-sight deposition, which allows more complex geometries to be coated, or even multiple parts at once. The pseudo-columnar microstructure that can be produced with PS-PVD is a possible alternative to EB-PVD. However, before PS-PVD can be used to its full potential, its mechanical properties and behavior must be understood. This work contributes to this understanding by characterizing PS-PVD TBCs that have been thermally cycled to simulate multiple lifetimes (0, 300, and 600 thermal cycles). Residual stress in the thermally grown oxide (TGO) layer is characterized by photoluminescence piezospectroscopy as TGO residual stress is correlated with the lifetime of the coating. Residual stress in the top coat is characterized by Raman spectroscopy, because this stress drives cracking in the top coat that can lead to failure. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) are performed to observe microstructural and phase evolution to provide context and possible explanations for the stress results. In addition, EB-PVD samples of the same thermal cycling history are characterized in the same way so that PS-PVD can be benchmarked against the industry standard. The compressive residual stress in the TGO in both coatings was relieved with thermal cycling due to the TGO lengthening as well as microcracking. The PS-PVD samples had slightly lower TGO stress than the EB-PVD, which is attributed to the greater extent of cracking within the TGO, whereas cracking in the EB-PVD samples was at the TGO/topcoat interface. The PS-PVD cycled samples had significant cracking within the topcoat near the TGO due to both greater porosity than EB-PVD samples and regions of unmelted particles that provide little resistance to cracking. The greater convolution of the TGO in the PS-PVD samples results in greater out-of-plane tensile stresses that cause crack initiation, as well as diverts cracks away from the difficult-to-follow interface. The TGO stress results agree with existing literature and extend the thermal cycling beyond what has previously been reported for PS-PVD coatings, revealing a trend of stress relief and stress values similar to that of EB-PVD coatings in this study and in the literature. Residual stress in the topcoat for both coating types became increasingly compressive with thermal cycling, indicating loss of strain tolerance by sintering. The trend of the YSZ stress for both coating types to become more compressive with cycling and with depth agrees with the literature, and the thermal cycling is longer than has been previously reported for PS-PVD. The two coating types had quite different microstructures and crack modes as well as different as-deposited residual stresses, but after thermal cycling had similar stresses in both the TGO and top coat. No samples experienced spallation. These results indicate that, while PS-PVD coatings have different properties and behavior from EB-PVD coatings, they had comparable levels of damage to EB-PVD coatings of the same lifetime and are a viable alternative to EB-PVD. Further tuning of the processing parameters may result in PS-PVD coatings with even more similar behavior to EB-PVD coatings.
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Date Issued
2019
Identifier
CFE0007717, ucf:52429
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007717
Development of S-nitroso-N-acetylpenicillamine (SNAP) Impregnated Medical Grade Polyvinyl Chloride for Antimicrobial Medical Device Interfaces
Title
Development of S-nitroso-N-acetylpenicillamine (SNAP) Impregnated Medical Grade Polyvinyl Chloride for Antimicrobial Medical Device Interfaces.
Creator
Feit, Corbin, Brisbois, Elizabeth, Vaidyanathan, Raj, Kuebler, Stephen, University of Central Florida
Abstract / Description
In the clinical setting, polyvinyl chloride (PVC) accounts for 25% of all polymers used in medical device applications. However, medical devices fabricated with PVC, such as endotracheal tubes, extracorporeal circuits (ECCs), or intravenous catheters suffer from thrombosis and infection. Mortality associated with hospital associated infections (HAIs) exceed 100,000 deaths each year. One method to overcome these challenges is to develop bioactive polymers with nitric oxide (NO) release. Nitric...
Show moreIn the clinical setting, polyvinyl chloride (PVC) accounts for 25% of all polymers used in medical device applications. However, medical devices fabricated with PVC, such as endotracheal tubes, extracorporeal circuits (ECCs), or intravenous catheters suffer from thrombosis and infection. Mortality associated with hospital associated infections (HAIs) exceed 100,000 deaths each year. One method to overcome these challenges is to develop bioactive polymers with nitric oxide (NO) release. Nitric oxide exhibits many physiological roles including, antibacterial, antithrombic, anti-inflammatory activity. In this study, Tygon(&)#174; PVC tubing was impregnated with a NO donor molecule, S-nitroso-N-acetylpenicillamine (SNAP), via a simple solvent-swelling-impregnation method, where polymer samples were submerged in a SNAP impregnation-solvent (methanol, acetone, plasticizer). An additional topcoat of a biocompatible CarboSil 2080A (CB) was applied to reduce SNAP leaching. The SNAP-PVC-CB were characterized for NO release using chemiluminescence, leaching with UV-Vis spectroscopy, surface characterization with scanning electron microscopy, tensile strength analysis, stability during storage and sterilization, and antimicrobial properties in vitro. The SNAP-PVC-CB exhibited NO flux of 4.29 (&)#177; 0.80 x 10-10 mol cm-2 min-1 over the initial 24 h under physiological conditions and continued to release physiological levels of NO for up 14 d (incubated in PBS at 37 (&)deg;C). The addition of CB-topcoat reduced the total SNAP leaching by 86% during incubation. Mechanical properties and surface topography remained similar to original PVC after SNAP-impregnation and application of CB-topcoat. After ethylene oxide sterilization and 1-month storage, SNAP-PVC-CB demonstrated excellent SNAP stability (ca. 90% SNAP remaining). In a 24 h antibacterial assay, SNAP-PVC reduce viable bacteria colonization (ca. 1 log reduction) of S. aureus and E. coli compared to PVC controls. This novel method for SNAP-impregnation of medical grade plasticized PVC holds great potential for improving the biocompatibility of post-fabricated PVC medical devices.
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Date Issued
2019
Identifier
CFE0007887, ucf:52782
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007887
Enhancement of Bandwidth and Laser Deflection Angle of Acousto-optic Deflectors by Dynamic Two-dimensional Refractive Index Modulation
Title
Enhancement of Bandwidth and Laser Deflection Angle of Acousto-optic Deflectors by Dynamic Two-dimensional Refractive Index Modulation.
Creator
Wang, Tiansi, Kar, Aravinda, Likamwa, Patrick, Moharam, Jim, Vaidyanathan, Raj, University of Central Florida
Abstract / Description
Acousto-Optic Deflectors (AODs) are inertialess optical solid state devices that have advantages over conventional mechanically controlled mirror-based deflectors in numerous scientific and industrial applications. These applications include fluorescence microscopy, sensing, variable-focus lens, photolithography and laser materials processing. AODs are currently operated with a single piezoelectric transducer that modulates the refractive index only in one direction. This operating principle...
Show moreAcousto-Optic Deflectors (AODs) are inertialess optical solid state devices that have advantages over conventional mechanically controlled mirror-based deflectors in numerous scientific and industrial applications. These applications include fluorescence microscopy, sensing, variable-focus lens, photolithography and laser materials processing. AODs are currently operated with a single piezoelectric transducer that modulates the refractive index only in one direction. This operating principle limits the performance of AODs to a narrow acoustic bandwidth of the transducer and a small angle of laser deflection governed by the Bragg diffraction. To overcome these two limitations, the operation of AODs with phased array ultrasonic transducers is analyzed in this study. Only the amplitude and frequency of the acoustic waves are modulated in conventional AODs. The phased array mechanism enables modulating the acoustic phase in addition to the amplitude and frequency modulations. The latter two phenomena affect the refractive index variation and its periodicity in the AOD medium, respectively, and the phase modulation produces tilted wavefronts due to diffraction and interference of the ultrasonic waves. Consequently, a tilted phase grating is formed inside the AOD device and the tilt angle automatically modifies the laser incident angle on the grating compared to the original angle of incidence on the AOD device. The acoustic frequency and amplitude are, therefore, modulated to achieve the Bragg diffraction under the new angle of incidence and maximize the diffraction efficiency, respectively. The phase grating can be tilted at any arbitrary angle by steering the ultrasonic beam in different directions. The beam steering can be achieved by operating the transducers with various time delays to generate ultrasonic waves of different phases. Due to the diffraction pattern of the ultrasonic intensity distribution, the refractive index varies both longitudinally and transversely to the beam steering direction, and two-dimensional refractive index modulation occurs when the transducers are very long in the third dimension. The acoustic waves affect the refractive index through the photoelastic effect by inducing mechanical strain waves in the AOD medium. The ultrasonic beam steering and the mechanical strain are determined using a modified Rayleigh-Sommerfeld diffraction integral. This integral represents the mechanical displacement vector field produced by ultrasonic waves in solid media. An analytic expression is obtained for the displacement field and the resulting strain distribution is calculated using this expression. Based on the strain and the photoelastic constants, the two-dimensional variation in the refractive index is determined for single-crystal paratellurite TeO2 which is an excellent AOD material. Conventional two-dimensional coupled mode theory of AOD, which is based on only one-dimensional refractive index modulation, is extended in this study to analyze the effect of two-dimensional index variation on the performance of AODs. The diffraction efficiency and the laser beam deflection angle are determined for both plane waves and Gaussian laser beams by obtaining analytic solutions for the coupled mode equations. The diffraction efficiency is found to be nearly unity over a broad range of the acoustic frequency, and the deflection angle can also be increased by steering the ultrasonic beam at large angles.
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Date Issued
2017
Identifier
CFE0006672, ucf:51219
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006672
Graphene Oxide Reinforcement in Plasma Sprayed Nickel-5%Aluminum Coatings
Title
Graphene Oxide Reinforcement in Plasma Sprayed Nickel-5%Aluminum Coatings.
Creator
Ward, David, Seal, Sudipta, Vaidyanathan, Raj, Heinrich, Helge, Zhai, Lei, University of Central Florida
Abstract / Description
Metallic plasma sprayed coatings are widely used in the aerospace industry for repair on worn engine components. However, the inherent defects in these coatings limit the variety of repairs and reduce the service life of the repaired parts. A potential solution to overcome this problem is to mix small amounts of inexpensive graphene oxide in the powder feedstock. The incredible strength to weight ratio of graphene oxide makes it a viable additive to improve mechanical properties of metallic...
Show moreMetallic plasma sprayed coatings are widely used in the aerospace industry for repair on worn engine components. However, the inherent defects in these coatings limit the variety of repairs and reduce the service life of the repaired parts. A potential solution to overcome this problem is to mix small amounts of inexpensive graphene oxide in the powder feedstock. The incredible strength to weight ratio of graphene oxide makes it a viable additive to improve mechanical properties of metallic plasma sprayed coatings. The powder system chosen for this research is Nickel-5Aluminum since it is a common coating for such repairs. The greatest challenge was retaining graphene oxide, which combusts at 400(&)deg;C, while melting the Nickel above 1450(&)deg;C using a high temperature plasma plume. Graphene oxide was successfully retained in the coatings using either of two configurations: (1) Injecting the graphene oxide powder via solution suspension separately from the metal powder, or (2) Installing a shroud on the front of the plasma gun and backfilling with Argon to inhibit combustion. The uniquely designed solution suspension configuration resulted in a higher deposition efficiency of graphene oxide while the inert shroud configuration had a more homogeneous distribution and retention of graphene oxide in the coatings. The best overall coating was achieved using the inert shroud configuration using a powder mixture containing 2% weight Edge Functionalized Graphene Oxide. Vickers microhardness increased 46% and tensile adhesion strength increased 26% over control samples. This is possible due to the mechanisms of dislocation strengthening and stress transfer previously reported in graphene oxide reinforced Aluminum composites formed by flake powder metallurgy. It was also observed that the energy released by the combustion of graphene oxide helps to uniformly melt the Nickel particles and improve the coating microstructure, allowing for more forgiving spray parameters. The methods developed and results attained in this research open opportunities for graphene oxide to be added as inexpensive reinforcements to other metallic compositions for widespread use in metal matrix composite manufacturing.
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Date Issued
2014
Identifier
CFE0005901, ucf:50857
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005901
Multi-axial Thermomechanical Characterization of Shape Memory Alloys for Improved Stability
Title
Multi-axial Thermomechanical Characterization of Shape Memory Alloys for Improved Stability.
Creator
Nicholson, Douglas, Vaidyanathan, Raj, Kumar, Ranganathan, Chen, Ruey-Hung, University of Central Florida
Abstract / Description
Shape recovery in shape memory alloys (SMAs) occurs against external stress by means of a reversible thermoelastic solid state phase transformation typically between so-called austenite, martensite and R-phases. The ability to do work enables their use as high-force actuators in automotive and aerospace applications while superelastic NiTi is of interest in biomedical devices such as stents. Both R-phase and martensite can detwin, reorient and undergo a thermal or stress induced...
Show moreShape recovery in shape memory alloys (SMAs) occurs against external stress by means of a reversible thermoelastic solid state phase transformation typically between so-called austenite, martensite and R-phases. The ability to do work enables their use as high-force actuators in automotive and aerospace applications while superelastic NiTi is of interest in biomedical devices such as stents. Both R-phase and martensite can detwin, reorient and undergo a thermal or stress induced transformation. For these reasons, it is difficult from ordinary macroscopic measurements to decouple elastic and inelastic contributions (from their respective phases) from the overall deformation. In situ neutron diffraction is ideally suited to probing these microstructural and micromechanical changes while they occur under external stress fields. Despite SMAs typically operating under multi-axial stress states in applications, most previous in situ neutron diffraction based investigations on SMAs have been limited to homogenous stress states as a result of uniaxial loading. The current investigation spatially maps thermoelastic deformation mechanisms during heating and uniaxial/torsional loading of shape memory and superelastic NiTi by recourse to in situ neutron diffraction, performed at Oak Ridge and Los Alamos National Laboratories. SMA spring actuators were also used to experimentally validate the ability of a recently developed model to predict the evolutionary deformation response under multi-axial loading conditions.By recourse to in situ neutron diffraction, martensite variants were tracked during isothermal, isobaric, and isostrain loading in shape memory NiTi. Results show variants were equivalent for the corresponding strain and more importantly, the reversibility and equivalency was immediately evident in variants that were first selected isobarically but then reoriented to a near random self-accommodated structure by isothermal deformation. Variants selected isothermally were not significantly affected by a subsequent thermal cycle under constant strain. During uniaxial/torsional loading and heating, thermoelastic deformation mechanisms in non-uniform states of stress in superelastic NiTi were spatially mapped. The preferred selection of R-phase variants by reorientation and detwinning processes were equivalent for the corresponding strain (in tension and compression) and was reversed by isothermal loading. The variants selected were consistent between uniaxial and torsional loading when the principal stress directions of the stress state were considered (for the crystallographic directions considered here). The similarity in general behavior between uniaxial and torsional loading, in spite of the implicit heterogeneous stress state associated with torsional loading, pointed to the ability of the reversible thermoelastic transformation to accommodate both stress and strain mismatch associated with deformation.Overall, various thermomechanical combinations of heating and loading sequences yielded the same final texture (preferred selection of variants), which highlighted the ability to take different paths yet still obtain the desired response while minimizing irrecoverable deformation mechanisms. These paths have implications for minimizing the number of cycles required to train an SMA, which limits the amount of work required for stabilizing their evolutionary response thereby increasing the fatigue life and overall durability of the SMA. This finding is valuable to the aerospace and medical device industries where SMAs find current application.
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Date Issued
2017
Identifier
CFE0006952, ucf:51676
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006952
SYNTHESIS AND CHARACTERIZATION OF STABLE AND METASTABLE PHASES IN Ni- AND Fe-BASED ALLOY SYSTEMS BY MECHANICAL ALLOYING
Title
SYNTHESIS AND CHARACTERIZATION OF STABLE AND METASTABLE PHASES IN Ni- AND Fe-BASED ALLOY SYSTEMS BY MECHANICAL ALLOYING.
Creator
Al-Joubori, Ahmed, Challapalli, Suryanarayana, Vaidyanathan, Raj, Gou, Jihua, Bai, Yuanli, Lin, Kuo-Chi, University of Central Florida
Abstract / Description
Mechanical Alloying (MA) is a process that involves repeated cold welding, fracturing and rewelding of powder particles in a high-energy ball mill and has been used extensively to synthesize both stable (equilibrium) and metastable phases in a number of alloy systems. This is due to its ability to achieve many effects simultaneously, viz., reduction in grain size, introduction of a variety of crystal defects, disordering of the lattice, and modifying the crystal structures of materials; all...
Show moreMechanical Alloying (MA) is a process that involves repeated cold welding, fracturing and rewelding of powder particles in a high-energy ball mill and has been used extensively to synthesize both stable (equilibrium) and metastable phases in a number of alloy systems. This is due to its ability to achieve many effects simultaneously, viz., reduction in grain size, introduction of a variety of crystal defects, disordering of the lattice, and modifying the crystal structures of materials; all these allowing alloying and phase transformations to occur in powders. In this Dissertation, we have synthesized a number of different alloy phases in Ni- and Fe-based alloy systems using MA.The as-received, blended, and milled powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy techniques to obtain information about the overall microstructure and chemical compositions. The NiX2 (X = Ge and Si) phases were synthesized in the Ni-Ge and Ni-Si systems. MA of Ni-Ge powder blends was investigated to study phase evolution as a function of milling time. On milling the powders for 5 h, the equilibrium NiGe phase started to form, and its amount in the powder increased with increasing milling time. On milling for about 60 h, the equilibrium intermetallic NiGe and Ge powder particles reacted to form the metastable NiGe2 phase. However, on milling for a longer time (75 h), the metastable phase transformed back to the equilibrium NiGe phase.Synthesis of the NiSi2 intermetallic phase depended on the Si content in the initial powder blend. For example, while in the Ni-60 at.% Si powder blend, only the NiSi phase was present homogeneously, the powder blend of the Ni-67 at.% Si composition contained the NiSi phase along with a small amount of unreacted Si. But in the Ni-75 at.% Si and Ni-80 at% compositions, the NiSi phase that had formed earlier (after 2 h of milling) and the remaining free Si powder reacted to form the equilibrium intermetallic NiSi2 phase. This constitution in the milled powder has been attributed to a partial loss of Si content during MA. Formation of Ni(Si) solid solutions with a solubility of about 18.2 at.% and 20.6 at.% for the Ni-75 at.% Si and Ni-80 at.% Si powder blends, respectively, was also achieved in the early stages of MA.In the Fe-C system, we were able to synthesize ferrite, cementite, and mixtures of the two phases. We were able to obtain the Fe-C solid solution phase (ferrite) with a BCC structure and the cementite phase with an orthorhombic structure in the eutectoid Fe-0.8 wt. % C composition, while a homogeneous cementite phase had formed at the higher carbon content of Fe-7.0 wt. % C after 30 h of milling time.In the case of the Fe-18Cr-xNi (x = 8, 12, and 20) system, the current investigation showed that the phase constitution depended significantly on the Ni content in the powder blend. Whereas mostly the martensite or the ferrite and austenite phase mixture was present at lower Ni contents, a completely homogeneous austenite phase was present in the alloy with 20% Ni.
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Date Issued
2016
Identifier
CFE0006244, ucf:51059
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006244
An uncooled mid-wave infrared detector based on optical response of laser-doped silicon carbide.
Title
An uncooled mid-wave infrared detector based on optical response of laser-doped silicon carbide.
Creator
Lim, Geunsik, Kar, Aravinda, Coffey, Kevin, Vaidyanathan, Raj, Dhere, Neelkanth, Likamwa, Patrick, University of Central Florida
Abstract / Description
This dissertation focuses on an uncooled Mid-Wave Infra-Red (MWIR) detector was developed by doping an n-type 4H-SiC with Ga using the laser doping technique. 4H-SiC is one of the polytypes of crystalline silicon carbide, a wide bandgap semiconductor. The dopant creates an energy level of 0.30 eV, which was confirmed by optical spectroscopy of the doped sample. This energy level corresponds to the MWIR wavelength of 4.21 um. The detection mechanism is based on the photoexcitation of electrons...
Show moreThis dissertation focuses on an uncooled Mid-Wave Infra-Red (MWIR) detector was developed by doping an n-type 4H-SiC with Ga using the laser doping technique. 4H-SiC is one of the polytypes of crystalline silicon carbide, a wide bandgap semiconductor. The dopant creates an energy level of 0.30 eV, which was confirmed by optical spectroscopy of the doped sample. This energy level corresponds to the MWIR wavelength of 4.21 um. The detection mechanism is based on the photoexcitation of electrons by the photons of this wavelength absorbed in the semiconductor. This process modifies the electron density, which changes the refraction index and, therefore, the reflectance of the semiconductor is also changed. The change in the reflectance, which is the optical response of the detector, can be measured remotely with a laser beam such as a He-Ne laser. This capability of measuring the detector response remotely makes it a wireless optical detector. The variation of refraction index was calculated as a function of absorbed irradiance based on the reflectance data for the as-received and doped samples. A distinct change was observed for the refraction index of the doped sample, indicating that the detector is suitable for applications at 4.21 um wavelength. The Ga dopant energy level in the substrate was confirmed by optical absorption spectroscopy. Secondary ion mass spectroscopy (SIMS) of the doped samples revealed an enhancement in the solid solubility of Ga in the substrate when doping is carried out by increasing the number of laser scans. Higher dopant concentration increases the number of holes in the dopant energy level, enabling photoexcitation of more electrons from the valence band by the incident MWIR photons. The detector performance improves as the dopant concentration increases from 1.15(&)#215;1019 to 6.25(&)#215;10^20 cm^-3. The detectivity of the optical photodetector is found to be 1.07(&)#215;10^10 cm?Hz^1/2/W for the case of doping with 4 laser passes. The noise mechanisms in the probe laser, silicon carbide MWIR detector and laser power meter affect the performance of the detector such as the responsivity, noise equivalent temperature difference (NETD) and detectivity. For the MWIR wavelength 4.21 and 4.63 um, the experimental detectivity of the optical photodetector of this study is found to be 1.07(&)#215;10^10 cm?Hz^1/2/W, while the theoretical value is 2.39(&)#215;10^10 cm?Hz^1/2/W. The values of NETD are found to be 404.03 and 15.48 mK based on experimental data for an MWIR radiation source of temperature 25(&)deg;C and theoretical calculation respectively.The doped SiC also has a capability of gas detection since gas emission spectra are in infrared range. Similarly, the sensor is based on the semiconductor optics principle, i.e., an energy gap is created in a semiconductor by doping it with an appropriate dopant to ensure that the energy gap matches with an emission spectral line of the gas of interest. Specifically four sensors have been fabricated by laser doping four quadrants of a 6H-SiC substrate with Ga, Al, Sc and P atoms to detect CO2, NO, CO and NO2 gases respectively. The photons, which are emitted by the gas, excite the electrons in the doped sample and consequently change the electron density in various energy states. This phenomenon affects the refraction index of the semiconductor and, therefore, the reflectivity of the semiconductor is altered by the gas. The optical response of this semiconductor sensor is the reflected power of a probe beam, which is a He-Ne laser beam in this study. The CO2, NO, CO and NO2 gases change the refraction indices of Ga-, Al-, Sc- and Al-doped 6H-SiC, respectively, more prominently than the other gases tested in this study. Hence these doped 6H-SiC samples can be used as CO2, NO, CO and NO2 gas sensors respectively.
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Date Issued
2014
Identifier
CFE0005519, ucf:50310
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005519
Advanced Nanoscale Characterization of Plants and Plant-derived Materials for Sustainable Agriculture and Renewable Energy
Title
Advanced Nanoscale Characterization of Plants and Plant-derived Materials for Sustainable Agriculture and Renewable Energy.
Creator
Soliman, Mikhael, Tetard, Laurene, Vaidyanathan, Raj, Kang, Hyeran, Santra, Swadeshmukul, Zhai, Lei, Chumbimuni Torres, Karin, University of Central Florida
Abstract / Description
The need for nanoscale, non-invasive functional characterization has become more significant with advances in nano-biotechnology and related fields. Exploring the ultrastructure of plant cell walls and plant-derived materials is necessary to access a more profound understanding of the molecular interactions in the systems, in view of a rational design for sustainable applications. This, in turn, relates to the pressing requirements for food, energy and water sustainability experienced...
Show moreThe need for nanoscale, non-invasive functional characterization has become more significant with advances in nano-biotechnology and related fields. Exploring the ultrastructure of plant cell walls and plant-derived materials is necessary to access a more profound understanding of the molecular interactions in the systems, in view of a rational design for sustainable applications. This, in turn, relates to the pressing requirements for food, energy and water sustainability experienced worldwide.Here we will present our advanced characterization approach to study the effects of external stresses on plants, and resulting opportunities for biomass valorization with an impact on the food-energy-water nexus.First, the adaption of plants to the pressure imposed by gravity in poplar reaction wood will be discussed. We will show that a multiscale characterization approach is necessary to reach a better understanding of the chemical and physical properties of cell walls across a transverse section of poplar stem. Our Raman spectroscopy and statistical analysis reveals intricate variations in the cellulose and lignin properties. Further, we will present evidence that advanced atomic force microscopy can reveal nanoscale variations within the individual cell wall layers, not attainable with common analytical tools. Next, chemical stresses, in particular the effect of Zinc-based pesticides on citrus plants, will be considered. We will show how multiscale characterization can support the development of new disease management methods for systemic bacterial diseases, such as citrus greening, of great importance for sustainable agriculture. In particular, we will focus on the study of new formulations, their uptake and translocation in the plants following different application methods. Lastly, we will consider how plant reactions to mechanical and chemical stresses can be controlled to engineer biomass for valorization applications. We will present our characterization of two examples: the production of carbon films derived from woody lignocellulosic biomass and the development of nanoscale growth promoters for food crop. A perspective of the work and discussion of the broader impact will conclude the presentation.
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Date Issued
2018
Identifier
CFE0007415, ucf:52717
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007415
Theoretical and Experimental Studies for Tailoring the Electromagnetic Surface Properties of Conductive Materials
Title
Theoretical and Experimental Studies for Tailoring the Electromagnetic Surface Properties of Conductive Materials.
Creator
Jennings, Jeffrey, Vaidyanathan, Raj, Kar, Aravinda, Coffey, Kevin, Challapalli, Suryanarayana, Brisbois, Elizabeth, Yu, Xiaoming, University of Central Florida
Abstract / Description
Induction in leaded, implanted medical devices exposed to radio frequency (RF) magnetic fields during magnetic resonance imaging (MRI) produce Joule heating in adjacent tissues causing various issues, including death. Given the importance of MRI as a diagnostic tool and the growth in leaded device-related treatments, identification of a solution ensuring their compatibility is of great interest. Electromagnetic (EM) surface property tailoring in lead materials to change their inductive...
Show moreInduction in leaded, implanted medical devices exposed to radio frequency (RF) magnetic fields during magnetic resonance imaging (MRI) produce Joule heating in adjacent tissues causing various issues, including death. Given the importance of MRI as a diagnostic tool and the growth in leaded device-related treatments, identification of a solution ensuring their compatibility is of great interest. Electromagnetic (EM) surface property tailoring in lead materials to change their inductive response by adding functionally-graded, heterogeneous surface layers is a possible solution. However, non-uniform EM properties introduce two challenges: the added complexity of analyses and characterization of the graded region. This dissertation addresses these complexities.An Helmholtz coil and other loops positioned in a coaxial array were used to create and monitor inductive fields that were mathematically related to the induced current in closed, circular loops with electrical conductivities ranging from 1.0 to 57 megaSiemens per meter. Magnetic flux densities up to 14 microTesla at frequencies from 30 to 100 MHz were evaluated for specimens with varying loop and wire diameters. Induced current results show a linear relationship with flux density and strongly depend on the sample geometry, but not on conductivity. Trends within the data matched well with those predicted by theory that considered such a loop.An equivalent length, semi-analytical approach modeled induced current through a graded EM property region and considered effective conductivities. Predicted results for transmissivity through Pt-doped titanium foils and effective conductivity in round wire Sn-modified Cu samples show good agreement with experimental data. The Joule heating experiment used for wire testing also demonstrates a means for characterizing conductor surface properties. Two new technologies derived from this research including an RF magnetic field imaging technique and a contoured loop array for applying therapeutic controlled RF magnetic fields are also described.
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Date Issued
2018
Identifier
CFE0007756, ucf:52378
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007756