Deformation induced structural change of quenched ω phase in Ti-20 mass%Mo alloy

Abstract

Tensile testing the Ti-20 mass%Mo alloy quenched from 1223 K was performed at 293 K, 623 K and 723 K to investigate the effects quenched ω phase on the mechanical properties. Nominal stress-strain curves after yielding became horizontal with increasing deformation temperature. When deformed at 293 K the dislocation structure observed by TEM had a feature of planner slip concentrated in a banded area. When deformed at elevated temperatures, on the other hand, wavy dislocations were observed to form a cell structure. The specimen deformed after thinning for TEM foil showed the formation of a band product which consisted a single ω-c$/ variant in the vicinity of the crack tip. In situ tensile test in TEM revealed that ω-IC$/ changed into ω-c$/ as deformation progressed. It is considered from these results that deformation behavior at elevated temperatures approached to that of bcc metals because of the stabilization of the β phase, and that the deformation behavior at room temperature was affected by the band product which consists of a single ω-c$/ variant transformed from ω-IC$/. It is further suggested that ω-c$/ can play an obstructing role to the ductility.