Microstructural evolution of Ti–44.5Al–4Nb–1Mo–0.1B powder and its correlation with hot isostatic pressing structure

Powder metallurgy has become a potential fabrication method for TiAl alloy, and pre-alloyed powder, as the raw material, is a crucial factor influencing the quality of powder metallurgy products. In this study, the original microstructural characteristics and microstructure evolution during heat treatment of Ti–44.5Al–4Nb–1Mo–0.1B powder were investigated in detail, and the correlation between the powder structure and as-HIPed alloy was discussed. The pre-alloyed powders were identified into two types: martensitic and dendritic powders, differing in phase composition and microstructural characteristics, which are highly associated with particle size distribution. During the heating process, the variations in the initial powders affect the evolution of the microstructure toward equilibrium conditions, while with the increase of temperature, the structural differences are eliminated, and finally transformed into the full lamellar structures at 1290 °C. Further validation was taken by the HIP experiment. With the effect of pressure on the increasing phase transformation temperature, the full lamellar structure was obtained after HIP at 1320 °C. This research provides a reference for the powder and process parameter determination in the HIP processing of TiAl alloys.