Influence of Cold Caliber Rolling on α Phase Formation in Metastable β Ti Alloys

Abstract

This study elucidates an effect of cold caliber rolling on microstructures refinement in metastable titanium alloys. Ingots of Ti-5Al-5V-5Mo-3Cr (mass%), Ti-5Al-5V-5Mo-3Cr-0.5Fe and Ti-15Mo were produced by cold crucible levitation melting and formed into 17 mm square bars. They were then caliber rolled into 11.8 mm square bars at room temperature. Some cold caliber rolled bars were solution treated at above the transus and aged at 923K (STA). Others were directly aged after the cold caliber rolling (DA). The STA samples showed a heterogeneous distribution of coarse and fine acicular phases with primarily formed phase along the grain boundaries, while the DA samples had a more homogeneous formation of equiaxed phase. This is thought to be caused by the presence of a high density of dislocations and shear bands resulted from the cold caliber rolling. The DA samples showed higher yield stress and ultimate tensile strength than those in the STA condition.