Adiabatic shear localization in titanium and Ti-6 pct Al-4 pct V alloy
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I.
INTRODUCTION
AN "adiabatic
shear.band" has been defined j as a strain localization phenomenon generally attributed to a plastic instability arising from thermal softening during adiabatic or quasi-adiabatic deformation. Adiabatic shear bands may occur in such diverse areas as ballistic impact, explosive fragmentation machining, grinding, high-velocity fabrication, wear, and low-temperature deformation. While they have been observed since the beginning of this century (as reported by Reference 2) and described by Trent 3 in 1941, their discovery is usually attributed to Zener and Hollomon, 4 in 1944. Reviews on the subject have been published by Bedford et a l . , 2 Rogers, 3 and Olson et al. ~ The investigations on adiabatic shear bands have in general been conducted along two directions: mechanical and microstructural. The mechanical analyses are attempts at determining criteria for the formation of these instabilities of plastic flow. Following the qualitative description of Zener and Hollomon, 4 Recht, 5 Culver, 6 Erlich e t a l . , 7 Clifton, 8 and Bai 9 developed theoretical analyses for shear-band formation. Basinski,~~ Chin e t a l . , ~ and Argonl2 have investigated the phenomenon at low strain rates. Staker ~3recently compared theoretical predictions with actual observations for AISI 4340 steel in a number of heat treatment conditions. The microstructural characterization has been reported in numerous papers for a number of alloy systems. Rogers 3 has classified the bands into "deformed" and "transformed" types; for the latter type, the intense heat evolution, plastic deformation, and rapid cooling after deformation produce
H. ANDREW GREBE, formerly Graduate Student, Department of Metallurgical and Materials Engineering, New Mexico Institute of Mining and Technology, Socorro, NM 87801, is Works Metallurgist, Tubemakers of South Africa Ltd. Pty., Box 1905, Vereeniging 1930, South Africa. HAN-RYONG PAK, Assistant Professor, Department of Metallurgical and Materials Engineering, and MARC A. MEYERS, Associate Director, Center for Explosives Technology Research, are with New Mexico Institute of Mining and Technology, Socorro, NM 87801. Manuscript submitted March 23, 1984.
METALLURGICALTRANSACTIONS A
phase transformations. Critical to the understanding of adiabatic shear bands is the identification of the microstructure inside the bands. These bands being typically only a few micrometers thick have made this a difficult task, and transmission electron microscopy has been the principal tool. The first study, by Stock and Thompson,~4 dates from 1969. They identified shear instabilities in 2014 aluminum alloy in the aged (T6 condition) and overaged conditions. They found small regions resembling grains (0.3 to 0.6 p~m) with misorientations of 5 to 15 deg between them. These grains resembled very much the ones found by Thomas and Willens 15 after rapidly quenching molten aluminum. Craig and Stock 16investigated 70-30 brass subjected to impact and observed rings in the diffraction pattern; they identified el
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