Microstructure characterization of hot isostatic pressed Ti–6Al–4V alloy under uniaxial compression and post heat treatment

The microstructural evolution law and the α variant selection relationship, as well as the deformation mechanism of the HIPed Ti-6Al-4V alloy, were investigated under the conditions of thermal compression and subsequent heat treatment. The results showed that lamellar α phase bending/kinking and fragmentation were the main spheroidizing mechanisms in the α+β phase region (850°C and 920°C), DDRX occurred as the restoration mechanism in the near-β region (940°C), and the heterogeneous microstructure originated from the temperature gradient distribution. The strain rate clearly affected the dynamically recrystallized grain fraction and diameter, e.g... both the fraction and diameter increased at a lower strain rate. The acicular α precipitated from β phase at 940°C obeyed the Burgers relationship with β, and their misorientation angle intensified at approximately 60°. GBα formed by reducing the adjacent lamellar α misorientation angle; therefore, the GBα nucleation energy was lowest. The microhardness variation was relatively stable along the X direction at α+β phase region deformation, while oscillation appeared at near-β deformation, which can be explained by microstructure heterogeneity after thermal compression. For heat treatment, the trimodal microstructure appeared at 940°C/0.001 s-1/60% thermal compression and subsequent 950°C/1 h/WQ heat treatment, and the result might guide practical production to optimize mechanical properties.