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

Ti-5Al-5Mo-5 V-1Cr-1Fe near β titanium alloys containing a thick and thin lamellar α phase were hot compressed at 700–800 °C and strain rates of 10−3–10−1s−1. The influence of lamellar α on alloy deformation and microstructure evolution was investigated. The great impediment of thick lamellar α 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 α 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 α/β grain size<0.5 - 1.0 μm was prepared by introducing the thin lamellar α at a low deformation temperature to prevent the substantial dissolution of α. The thin lamellar α structures were easily fragmented into fine α grains. The ease with which dislocations were cut across the thin lamellar α enhanced the dislocation density in the small β regions among thin, disperse lamellar α regions, which further led to the formation of β subgrains by the slipping-climbing of dislocations. Subsequently, fine β grains formed through the subgrain rotation mechanism.