Regulating phase ratio of β/α and static recrystallization of Ti-5Al-5Mo-5Cr-3Nb-2Zr with high plasticity alloyed by vanadium

Abstract

To research the recrystallization mechanism without deformation of the α phase and control the phase ratio of β/α, Ti-5Al-5Mo-5Cr-3Nb-2Zr alloys with different vanadium contents were melted. The results indicate that with increasing vanadium content, the content and aspect ratio of the primary α (αp) and secondary α (αs) phases decrease, and the ratio of the β phase increases from 7% to 88%. The degree of recrystallization of αp and grain boundary α (αGB) phases increases, and their morphology changes from lath to equiaxed. The mechanism of static recrystallization is that the enrichment of V aggravates the local lattice strain and leads to the migration of the α phase interface. The V element aggravates the atomic size mismatch and the local lattice strain and reduces the β transition temperature of the enrichment region. The strength in the Ti-0 V alloy is the highest at ∼1056 MPa and then decreases. The Ti-2 V alloy had the highest toughness of ∼68.4 MPa·m1/2. The elongation of the Ti-6 V alloy is the highest at ∼16.1% due to the increase of β phase content and α phase recrystallization, which is ∼1.8 and ∼ 1.7 times that of the Ti-0 V and Ti-8 V alloys, respectively. The equiaxed αp phase and αs phase lead to shortening of the crack deflection path, and crack propagation is easier due to the increase of β phase content, which causes the crack propagation path to change from tortuous to straight.