Microstructure evolution and mechanical properties of Ti46.5Al2Cr1.8Nb-(W, B) alloys fabricated by spark plasma sintering and pulse current assisted isothermal forging

Abstract

γ-TiAl based alloys are promising materials for high-temperature components in aerospace applications. To enable good mechanical characteristics with optimized microstructures via a low-cost green manufacturing technology, alloys were fabricated via spark plasma sintering by adopting pre-alloyed powders and followed by pulse current assisted isothermal forging (PCAIF). The sintering temperature determined the phase transformation behavior and thus resulted in typical near gamma, duplex, near lamella, and fully lamella microstructures. Additionally, the multiscale microstructure which derived from the occurrence of dynamic recrystallization (DRX) in deformed powders during the densification process and the original powder boundaries (OPBs) deteriorated their mechanical properties, and could not be eliminated thoroughly by optimizing sintering parameters. After PCAIF, typical near gamma, duplex, and near lamella microstructures were obtained with increasing forging temperature. Particularly, the multiscale microstructure and OPBs were eliminated due to the collective occurrence of DRX. Therefore, when tensile tested at 800 °C, the fracture mechanism transformed from fracturing at the interface of multiscale microstructure or OPBs due to the stress concentration between the zone with large and small grain size into the micro-void development at the interfaces of deformation twin groups and the DRX grains, thus improved the elongation significantly.