Dynamic globularization mechanism during hot working of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy with lamellar microstructure

Abstract

In the present work, the isothermal compression of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy with lamellar microstructure was conducted at 980 °C and strain rate range of 0.01–10 s−1. Evolution of substructure during hot working was analyzed to investigate the dynamic globularization mechanism with the help of SEM and TEM techniques. The main conclusions are as follows: At 0.01 s−1, the globularization mechanism is a continuous dynamic recrystallization, which is formed by the combination of the penetration of the β phase into α lamella along the subgrain boundaries and the sliding between the subgrain boundaries. This process is accompanied by the coarsening of the globularized α phase. While in the strain rate range of 0.1–10 s−1, the globularization mechanisms are the segmentation of α lamella along the twin grain boundaries and the process of discontinuous dynamic recrystallization, and the final equiaxed microstructure is smaller than the initial thickness of α lamella. Moreover, with the increase of strain rate and the decrease of temperature, discontinuous dynamic recrystallization gradually becomes the dominant mechanism of globularization. The β phase undergoes dynamic recovery or continuous dynamic recrystallization at different strain rate, which results in the globularization of β lamellae. The α and β lamellae promote each other in globularization.