ω-assisted α phase and hardness of Ti-5Al-5Mo-5V-1Cr-1Fe during low temperature isothermal heat treatment after laser surface remelting

Abstract

Abstract The near-β titanium alloy Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511) was treated by laser surface remelting (LSR) with a series of holding times at 500 °C in order to study the growth behavior of ω-assisted α phase and its effect on mechanical properties. Transmission electron microscope and hardness test was used to characterize different phases and surface property of different samples. Results show that only a small quantity of athermal ω phases precipitate from β matrix at the remelted zone and there are incomplete collapsed {111}β lattice planes at the β/ω boundaries because Ti-55511 has low electron/atom ratio and high Al contents. So the athermal ω phase precipitated during LSR process has little effect on increasing surface hardness of Ti-55511. ω-Assisted nano-scaled α lamellas can be formed by the connection of some initial α phases at the early stage of low temperature isothermal heat treatment. And all the ω phase dissolved after 500°C/10min. Further increasing of holding times will cause volume fractions increase of the nano-scaled α lamellas, resulting in gradually improving hardness of the alloy at the remelted zone.