High-temperature microstructure stability and fracture toughness of TiAl alloy prepared via electron beam smelting and selective electron beam melting

Abstract

This study investigated the high-temperature microstructure stability of TiAl alloys fabricated by electron beam smelting (EBS) to understand the microstructural evolution of TiAl alloys that were fabricated by selective electron beam melting (SEBM) by comparing the microstructure of EBS- and SEBM-produced TiAl alloy samples. The results showed that with an increase in annealing temperature from 1050 °C to 1250 °C, the degradation of the (α2/γ) lamellar colony increased. When the annealing temperature was 1050 °C, ellipsoidal B2 precipitates occurred along the primary α2 lamellae and distributed uniformly within lamellar colonies. The microstructure transformed into (γ/B2) laths when the annealing temperature was 1250 °C. The effect of microstructure and constituent phase on the fracture toughness was investigated for EBS- and SEBM-produced TiAl alloy by observing the fracture path profiles. The EBS-produced TiAl alloy that was heat-treated at 1050 °C for 0.5 h showed the most excellent fracture toughness. The SEBM-fabricated TiAl alloy exhibited the worst fracture toughness due to the fine grain size, degraded lamellar colony, and coarsening γ lath. Finally, the toughening mechanisms for the different microstructures were discussed in detail.