Deformation kinetics of commercial Ti-50A (0.5 At. Pct Oeq) at low temperatures ( T <0.3T m )
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INTRODUCTION
THEdislocation mechanisms responsible for the strength of titanium and titanium alloys over a wide temperature range are of both scientific and technological interest. Commercial Ti-50A is of special interest because its total interstitial solute content (~0.5 at. pct Oeq1) is intermediate between those of other commercial titanium materials (e.g., Ti-35A and Ti-75A) and because many of the common commercial titanium alloys based on substitutional solutes (e.g., Ti-5A1-2.5Sn and Ti-6AI-4V) contain nearly the same total interstitial content. Hence, Ti-50A may be considered as the base material for such alloys, thereby providing the possibility of distinguishing the effects of the substitutional solutes on mechanical properties from those of the interstitials alone. The dislocation mechanisms governing the strength of Ti-50A at temperatures between 0.3 and 0.6Tin (600 to 1150 K) have been considered in a previous paper. 2 At intermediate temperatures (0.3 < T/Tm < 0.4) the yield stress was found to be relatively independent of temperature (and strain rate) and the stress-strain curve exhibited features (serrations, high strain hardening, and low total elongation) indicative of dynamic strain aging, which was concluded to be due primarily to oxygen, the major interstitial solute present in this material. At high temperatures (0.4 < T/T,~ < 0.6) the flow stress was governed by a self diffusion-controlled mechanism, which was concluded to be Weertman's dislocation glide and climb mechanism. The present paper is concerned with the rate-controlling dislocation mechanism in Ti-50A at low temperatures (T < 0.3Tin), i.e., the mechanism which governs the interrelationship between the flow stress, temperature, and strain rate for a constant structure (deformation kinetics) at temperatures below about 600 K, where diffusion of CHIH-AN YIN is with General Electric Corporation, Building 14-120B, Metal!urgical Laboratory, 2901 East Lake Road, Erie, PA 16531. M. DONER is with Detroit Diesel Allison Division, General Motors Corporation, Indianapolis, IN 46206. H. CONRAD is Head, Materials Engineering Department, North Carolina State University, P. O. Box 5427, Raleigh, NC 27650. Manuscript submitted March 31, 1983. METALLURGICALTRANSACTIONS A
neither interstitial solutes nor host atoms is expected to play a role. Of additional interest is the effect of grain size on the deformation kinetics. The results given in the present paper along with those in the earlier studies2 thus provide information on the deformation kinetics of Ti-50A over the entire temperature range of the CPH structure of this material. The approach employed in the present paper to evaluate the deformation kinetics of Ti-50A is based on the concept of thermally activated plastic flow. 3'4 An important parameter in this approach is the long-range internal stress, which is presumed to be given by the so-called athermal component of the flow stress, o-~. The method most commonly employed to obtain this component is the back-extrapolation technique. 5
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