Effects of Alloying Elements on Deformation Mode in Ti-V Based β Titanium Alloy System

Abstract

We have discussed the rule by which the predominant cold deformation modes of metastable β phase are governed depending on their chemical compositions through the examinations of the effects of Sn, Al, and Zr on β-quenched and slightly cold rolled microstructures in a Ti-V based alloy system. It seems in Ti-V binary alloys, that orthorhpmbic martensitic transformation temperatures Ms and Md are depressed far below room temperature by the athermal ω phase at over about 15% V. Tin and aluminum intrinsically lower these temperatures like vanadium. On the other hand, tin and aluminum simultaneously suppress the athermal ω phase of Ti-16V to first rise Md and even Ms up to above room temperature, respectively. The deformation mode of β phase consequently depends on both the Md temperature and the degree of suppression of the athermal ω phase formation. Alloys having a Md above room temperature undergo stress-induced martensitic transformation. As for alloys having a Md below room temperature, alloys where the athermal ω phase is sufficiently suppressed undergo slip, whereas alloys where it is not so done {332}〈113〉 twinning. Since aluminum strongly suppresses the athermal ω formation, increased AI additions change the deformation mode of Ti-16V from {332} 〈113〉 twinning to stress-induced martensitic transformation via a quenched α″ region or that of Ti-16V-4Sn from stress-induced martensitic transformation to slip. On the other hand, since tin does not suppress it so much as aluminum, increased Sn additions first change the deformation mode of Ti-16V from {332}〈113〉 twinning to stress-induced martensitic transformation but subsequently revive {332} 〈113〉 twinning again before slip. The deformation mode of Ti-V-Al-Sn alloys can be interpreted by superposing the effects of V, Al, and Sn. Zirconium also depresses martensitic transformation temperatures and Ti-14V-6Zr undergoes stress-induced martensitic transformation. However, Ti-16V based Zr-added alloys undergo {332} 〈113〉 twinning in the wide range of Zr content because the athermal ω phase formation is rarely suppressed by zirconium. This interpretation has solved the discrepancy of the transition of deformation modes of β titanium alloys. © 1995, The Iron and Steel Institute of Japan. All rights reserved.