Elucidation of the microstructure evolution mechanism and new performance control strategy of powder metallurgy titanium alloy during hot deformation

Shuai Gao, Chao Zhao*, Shixing Wu, Bao Wang, Kejia Pan, Zhenwei Chen, Jinbao Long, Xuan Luo, Ning Li*

https://www.sciencedirect.com/science/article/pii/S0924013625000019

Abstract

To reveal the intrinsic relationship between hot workability and microstructure evolution, mechanical response and product performance of powder metallurgy titanium alloy, the Ti-6Al-3Nb-2Zr-1Mo (Ti6321) titanium alloy was designed and prepared under different deformation conditions. The three-dimension (3D) morphology evolution of micropores, dynamic phase transformation and thermomechanical processing map with visualisation functions were investigated. The results show that the hot deformation at low and medium strain rate (0.001–0.1 s−1) and two-phase zone (850–950 °C) is dominated by discontinuous dynamic recrystallisation (DDRX), complemented by dynamic recovery (DRV) and continuous dynamic recrystallisation (CDRX). Under high strain rate (1–10 s−1), a new α/β interface forms due to the formation of thermal erosion grooves on the surface of α phase, which eventually leads to grain boundary separation. Under the deformation conditions of the two-phase region (0.1 s−1, 900–1000 °C), the dynamic phase transformation (DP) preferentially nucleates and expands at the deformed α/β interface with a small radius of curvature. These deformation mechanisms jointly construct a thermomechanical processing (TMP) diagram with visual functions, and the optimal thermomechanical processing conditions are obtained, which provides a practical method for the subsequent heat treatment regulation to obtain a trimodal microstructure with excellent strength and toughness. It is shown that this method provides a reference for the forming and parametric design of high strength and toughness titanium alloys fabricated by powder metallurgy.