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

Abstract

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.

Keywords

• Thermal deformation & heat treatment
• Recrystallization
• α variants
• Trimodal microstructure