Effect of deformation and cooling on non-equilibrium microstructure evolution and phase-transition mechanism of Ti–6Al-2.5Mo-1.5Cr-0.5Fe-0.3Si

Abstract

In the process of non-isothermal deformation of titanium alloy, the microstructure evolution is very complicated, which has direct effect on the properties of the titanium alloy. This study examines the effects of pure cooling and coupled deformation and cooling at the initial temperature of 940 °C and the cooling rate of 5,50 °C/s, and the strain rate of 0.1, 10s−1 respectively, on the microstructure evolution of Ti–6Al-2.5Mo-1.5Cr-0.5Fe-0.3Si alloy (TC6) were investigated. The microstructure after cooling was characterised, and the mechanism of non-isothermal deformation on microstructure evolution and the mechanism of secondary α phase (αs) precipitation were revealed. The results show that the secondary α phase precipitates in large quantities after cooling to a certain temperature, and the secondary precipitated has an obvious inhibiting effect on the diffusion growth of the primary α phase (αp). Secondary α phases can be divided into lamellar and equiaxial types. When the temperature drops sharply, the fine secondary α phase can be precipitated directly from the β matrix. Due to the large number of dislocations generated by the deformation, many small secondary α phases can be generated during the rapid cooling process. The orientation relationship between α phase and β matrix is destroyed by the deformation, resulting in a weakening of the anisotropy, so that the secondary α phase remains equiaxial during the precipitation process.