Shock consolidation of mechanically alloyed amorphous Ti-Si powders
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INTRODUCTION
THE TisSi 3 intermetallic compound, because of its high hardness, good high-temperature properties (oxidation resistance and thermal conductivity), and extremely low specific weight, is a promising material for aerospace applications. E~1However, the inherent brittleness of this intermetallic compound has limited its fabrication into bulk products. The mechanical properties of TisSi 3 can be improved by refining the grain structure. Amorphous Ti-Si alloys have also been found to have sufficient ductility.L2] The possibility of amorphous phase formation by mechanical alloying in a metal-metalloid system such as Ti-Si has been investigated by Yan e t al.[31 using thermodynamics analysis and extensive experimental work. It is now possible to produce amorphous as well as nanocrystalline TiSi compounds in powder form using mechanical alloying techniques. [3,41 Subsequent consolidation of the nanocrystalline intermetallic compounds for producing bulk compacts is still difficult. On the other hand, consolidation of amorphous powders followed by controlled heat treatment can offer a possible solution for producing bulk compacts with nanocrystalline microstructures. Shock compaction has been extensively studied as a technique for consolidation of otherwise difficult to compact powders, [5,61 amorphous compounds,t7,8[ and Fe-based nanocrystalline alloys,t9[ for the purpose of attaining high densities and retaining the metastable state in the compacts. Shock consolidation has also been successfully used in the S.C. GLADE, formerly Undergraduate Research Assistant, School of Materials Science and Engineering, Georgia Institute of Technology, is Graduate Research Assistant, Materials Science Program, California Institute of Technology, Pasadena, CA 91125. N.N. THADHANI, Associate Professor, is with the School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0245. This article is based on a presentation made in the symposium "Dynamic Behavior of Materials," presented at the 1994 Fall Meeting of TMS/ASM in Rosemont, Illinois, October 3-5, 1994, under the auspices of the TMS-SMD Mechanical Metallurgy Committee and the ASM-MSD Flow and Fracture Committee. METALLURGICALAND MATERIALSTRANSACTIONSA
past to make bulk compacts of amorphous powders for subsequent crystallization to produce fine microcrystalline structures in Ni-Cr-Mo-B glass, forming alloys for improved corrosion and wear resistance,tx~ In a recent study, Yamasaki e t aL t41 shock compacted amorphous Tilo0_xSix (x = 10 to 60 at. pct) powder mixtures to produce partially crystallized Ti-Si alloy compacts of various compositions. Upon subsequent annealing at 1223 K, the compacts fully crystallized into 15- to 20-nm size crystallites, yielding a microhardness of 1700 HVN. The present study is an extension of Yamasaki's work, with the objective of demonstrating the use of shock compression for consolidation of mechanically alloyed amorphous Ti-Si powders and to show that a fine grain nanocrystalline structure can be r
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