Current Search:   Suryanarayana, C (x)

View All Items

  • CSV Spreadsheet
(1 - 2 of 2)
PROCESSING, MICROSTRUCTURAL AND MECHANICAL CHARACTERIZATION OF MECHANICALLY ALLOYED AL-ALUMINA NANOCOMPOSITES
Title
PROCESSING, MICROSTRUCTURAL AND MECHANICAL CHARACTERIZATION OF MECHANICALLY ALLOYED AL-ALUMINA NANOCOMPOSITES.
Creator
Katiyar, Pushkar, SURYANARAYANA, C., University of Central Florida
Abstract / Description
Aluminum-alumina nanocomposites were synthesized using mechanical alloying of blended component powders of pure constituents. This study was performed on various powder mixtures with aluminum as the matrix and alumina as the reinforcement with volume fractions of 20, 30, and 50 % and Alumina particle sizes of 50 nm, 150 nm, and 5 µm. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were used for the crystal structure and microstructural characterization of the...
Show moreAluminum-alumina nanocomposites were synthesized using mechanical alloying of blended component powders of pure constituents. This study was performed on various powder mixtures with aluminum as the matrix and alumina as the reinforcement with volume fractions of 20, 30, and 50 % and Alumina particle sizes of 50 nm, 150 nm, and 5 µm. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were used for the crystal structure and microstructural characterization of the powders at different stages of milling. Alumina powders with 50 nm and 150 nm particle size were predominantly of gamma-type, while Alumina of 5 µm size was of alpha-type. The main goal was to achieve uniform distribution of the alumina ceramic particles in the Al matrix, which was achieved on milling for 24 h in a SPEX mill or 100 h in a Fritsch Pulverisette planetary ball mill. The powders were consolidated in two stages: pre-compaction at room temperature followed by vacuum hot pressing (VHP) or hot isostatic pressing (HIP) techniques to a fully dense condition. The effect of reinforcement particle size and volume fraction on the stress-strain response, elastic modulus and yield strength of the composites was investigated. Nanoindentation and compression tests were performed to characterize the composite material. Yield strength of 515 MPa, compressive strength of 685 MPa and elastic modulus of 36 GPa were obtained from compression tests. Nanoindentation results gave the yield strength of 336 MPa, maximum shear stress of 194 MPa and an elastic modulus of 42 GPa. The low elastic modulus values obtained from the above tests might be because of localized yielding possibly due to residual stresses.
Show less
Date Issued
2004
Identifier
CFE0000128, ucf:46193
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000128
AMORPHOUS PHASE FORMATION IN MECHANICALLY ALLOYED FE-BASED SYSTEMS.
Title
AMORPHOUS PHASE FORMATION IN MECHANICALLY ALLOYED FE-BASED SYSTEMS.
Creator
Sharma, Satyajeet, Suryanarayana, C, University of Central Florida
Abstract / Description
ABSTRACT Bulk metallic glasses have interesting combination of physical, chemical, mechanical, and magnetic properties which make them attractive for a variety of applications. Consequently there has been a lot of interest in understanding the structure and properties of these materials. More varied applications can be sought if one understands the reasons for glass formation and the methods to control them. The glass-forming ability (GFA) of alloys can be substantially increased by a proper...
Show moreABSTRACT Bulk metallic glasses have interesting combination of physical, chemical, mechanical, and magnetic properties which make them attractive for a variety of applications. Consequently there has been a lot of interest in understanding the structure and properties of these materials. More varied applications can be sought if one understands the reasons for glass formation and the methods to control them. The glass-forming ability (GFA) of alloys can be substantially increased by a proper selection of alloying elements and the chemical composition of the alloy. High GFA will enable in obtaining large section thickness of amorphous alloys. Ability to produce glassy alloys in larger section thicknesses enables exploitation of these advanced materials for a variety of different applications. The technique of mechanical alloying (MA) is a powerful non-equilibrium processing technique and is known to produce glassy (or amorphous) alloys in several alloy systems. Metallic amorphous alloys have been produced by MA starting from either blended elemental metal powders or pre-alloyed powders. Subsequently, these amorphous alloy powders could be consolidated to full density in the temperature range between the glass transition and crystallization temperatures, where the amorphous phase has a very low viscosity. This Dissertation focuses on identifying the various Fe-based multicomponent alloy systems that can be amorphized using the MA technique, studying the GFA of alloys with emphasis on improving it, and also on analyzing the effect of extended milling time on the constitution of the amorphous alloy powder produced at earlier times. The Dissertation contains seven chapters, where the lead chapter deals with the background, history and introduction to bulk metallic glasses. The following four chapters are the published/to be published work, where the criterion for predicting glass formation, effect of Niobium addition on glass-forming ability (GFA), lattice contraction on amorphization, effect of Carbon addition on GFA, and observation of mechanical crystallization in Fe-based systems have been discussed. The subsequent chapter briefly mentions about the consolidation of amorphous powders and presents results of hot pressing and spark plasma sintering on one of the alloy systems. The final chapter summarizes the Dissertation and suggests some prospective research work that can be taken up in future. The Dissertation emphasizes the glass-forming ability, i.e., the ease with which amorphization can occur. In this work the milling time required for amorphization was the indicator/measure of GFA. Although the ultimate aim of this work was to consolidate the Fe-based amorphous alloy powders into bulk so as to undertake mechanical characterization, however, it was first necessary to study the glass forming aspect in the different alloy systems. By doing this a stage has been reached, where different options are available with respect to amorphous phase-forming compositions and the knowledge to improve glass-forming ability via the mechanical alloying technique. This will be ultimately useful in the powder compaction process into various shapes and sizes at optimum pressure and temperature. The study on mechanical crystallization indicates, or in a way defines, a limit to the process of amorphization, and it was also demonstrated that this phenomenon is more common in occurrence than and not as restricted as it was earlier reported to be.
Show less
Date Issued
2008
Identifier
CFE0002025, ucf:47630
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0002025