Hot Deformation of Ti-5Al-5Mo-5 V-1Cr-1Fe Near β Titanium Alloys Containing Thin and Thick Lamellar α Phase

Ti-5A1-5Mo-5 V-1Cr-1Fe near beta titanium alloys containing a thick and thin lamellar cc phase were hot compressed at 700-800 degrees C and strain rates of 10(-3)-10(-1)s(-1). The influence of lamellar cc on alloy deformation and microstructure evolution was investigated. The great impediment of thick lamellar a to plastic flow led to high deformation resistance, even though lamellar rotation caused a stress reduction at the beginning of continuous flow softening. In contrast, the integral and translational motion of thin lamellar a without apparent lamellar rotation presented a lower impediment to plastic flow. Moreover, the corresponding alloy exhibited low deformation resistance and gentle continuous flow softening. Furthermore, ultra-fine grained Ti-55511 with an alpha/beta grain size <0.5 - 1.0 mu m was prepared by introducing the thin lamellar alpha at a low deformation temperature to prevent the substantial dissolution of alpha. The thin lamellar a structures were easily fragmented into fine alpha grains. The ease with which dislocations were cut across the thin lamellar a enhanced the dislocation density in the small beta regions among thin, disperse lamellar a regions, which further led to the formation of beta subgrains by the slipping-climbing of dislocations. Subsequently, fine beta grains formed through the subgrain rotation mechanism. (C) 2013 Elsevier B.V. All rights reserved.