Effect of heat treatment on the microstructure and mechanical properties of Y₂O₃/Ti-22Al-25Nb composites

The effects of heat treatment on the microstructure and mechanical properties of forged Y₂O₃/Ti-22Al-25Nb composites were investigated. The results showed that after solution treatment at 920 °C, the microstructure consisted of numerous deformed grains and a small amount of fine recrystallized grains, with abundant fine lamellar O and B2 phases observed inside the grains. During solution treatment at 960 °C, elevated temperature promotes recovery and recrystallization of the B2 phase, forming a bimodal grain structure and significantly reducing the average grain size. Concurrently, the O-phase content within grains decreases, whereas the size of lamellar O-phase increases. Within the aging temperature range of 760°C-840 °C, the evolution mechanism of the B2 phase transitions with increasing temperature: recrystallized grains formed during solution treatment undergo continuous growth during low-temperature aging (760 °C), while recovery and recrystallization dominate at higher aging temperatures, ultimately refining the average grain size. At 840 °C, a single-phase B2 grain structure forms. Additionally, substantial acicular O-phase precipitates form in the B2 matrix during aging; however, elevated temperatures markedly suppress their precipitation, causing a sharp reduction in quantity. Tensile tests demonstrated that the highest ductility (18.7 %) was achieved after solution treatment at 960 °C, while the highest strength (1143 MPa) was obtained after aging at 760 °C. The sample subjected to solution treatment at 920 °C exhibited the optimal combination of strength (1133 MPa) and ductility (12.1 %). Fractographic analysis revealed that the fracture behavior of the composites was primarily influenced by the matrix microstructure.