Precipitation Behavior of ω Phase and ω→α Transformation in Near β Ti-5Al-5Mo-5V-1Cr-1Fe Alloy during Aging Process

Abstract

In this work, the precipitation behavior of the ω phase and ω→α transformation in Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511) alloy was investigated during isothermal aging at 450 °C. The results show that the α precipitates increase with the increasing of aging time, resulting from the β→α and ω→α transformations. The ω→→α transformation involves the formation and evolution of the isothermal ω phase. The formation of the isothermal ω phase occurs after 30 min and ends at 120 min, which is caused by the embryonic ω phase to isothermal ω phase transformation. Small angle neutron scattering (SANS) results indicates that the evolution of the isothermal ω phase goes through the increasing average size and aspect ratio from 24.7 to 47.0 nm and from 2.1 to 2.7 respectively, and the morphology evolution of the ω particle from ellipsoid to spindle-like. Moreover, the isothermal ω phase assists the α phase to nucleate at the ω/β interface, which involves the changes in elemental composition. The α phase is enriched in Al. Compared to the α phase, the element of Mo, V and Cr in the isothermal ω phase is lower. The Fe element is uniformly distributed in the isothermal ω phase and β matrix but lean in the α phase.