Abstract:To investigate the influence of heat treatment–induced microstructural evolution on the high-temperature mechanical behavior of Ti–48Al–2Cr–2Nb (TiAl-4822, at.%) alloy at 750 °C, specimens were fabricated via electron beam powder bed fusion (EB-PBF) and subsequently subjected to various heat treatment conditions to obtain distinct microstructures. The as-fabricated sample exhibited a heterogeneous bimodal structure composed of coarse γ bands and fine-grained duplex regions. After heat treatment at 1330 °C for 0.5 h followed by furnace cooling (FC), the alloy developed a homogeneous duplex microstructure with slightly coarsened grains. Increasing the heat treatment temperature to 1380 °C resulted in pronounced grain growth and the formation of a fully lamellar structure. With rising temperature, α? phases tended to segregate along interlamellar or intergranular regions, establishing the typical Blackburn orientation relationship with the γ phase. Mechanical testing revealed that hardness increased with heat treatment temperature, whereas both tensile strength and ductility at 750 °C decreased compared with the as-fabricated condition. The as- fabricated sample demonstrated superior high-temperature mechanical performance, achieving a tensile strength of 654.67 ± 17.01 MPa and an elongation of 42.5 ± 2.29%, primarily due to the fine γ grains and dense intragranular lamellae formed during rapid solidification. During heat treatment, the α? and γ phases coarsened through orientation-dependent growth to minimize interfacial energy, leading to lamellar thickening. The resulting coarsened lamellae and α? phase enrichment at grain boundaries and interlamellar interfaces served as preferential sites for crack initiation and propagation, thereby reducing ductility. This study elucidates the intrinsic correlations among heat treatment, microstructure, and mechanical behavior in EB-PBF TiAl-4822 alloy, providing valuable insights into tailoring the microstructure and optimizing the high-temperature performance of γ-TiAl alloys through thermal processing