The effect of microstructure evolution on the high-temperature mechanical properties and creep behavior of Y2O3-bearing alloy

Abstract

In this study, various heat treatment processes were employed to adjust the ratio of blocky γ phase to α₂/γ lamellae and to create conditions conducive to the precipitation of Y₂O₃ nanoparticles. The aim was to investigate the influence of microstructure evolution on the high-temperature mechanical properties and creep behavior of the Ti-48Al-2Cr-2Nb-0.05Y₂O₃ alloy. As the holding temperature increases from 1200 °C to 1350 °C, the content of the blocky γ phase decreases from 61.49 % to 1.12 %, resulting in the formation of nearly duplex (NDP) microstructure, duplex (DP) microstructure, nearly lamellar (NL) microstructure, and fully lamellar (FL) microstructure. The combination of elevated temperature conditions and increased crystal defects promotes the precipitation of Y₂O₃ nanoparticles, leading to the highest number of nanoscale reinforcements within the FL microstructure. As the heat-treated sample transitions from the NDP to FL microstructure, the ultimate tensile strength tested at 800 °C increases from 384 MPa to 668 MPa, while the creep life tested at 800 °C under 325 MPa improves from 10.8 h to 138.2 h. The elongation and creep strain initially increase and then decrease, with the heat-treated sample exhibiting an NL microstructure demonstrating the best high-temperature elongation of 21.48 % and the highest creep strain of 19.55 %. The favorable ductility and deformation capacity observed in the NL microstructure can be attributed to the cooperative deformation of the lamellar structure and its surrounding blocky γ phase. The excellent high-temperature strength and creep resistance of the FL microstructure result from the synergistic strengthening effect arising from a greater number of nanoscale Y₂O₃ precipitates and the highest content of lamellar colonies, which provide an effective pinning effect on dislocation movement. In comparison to commonly used reinforcements, the heat-treated TiAl alloys reinforced with dual-scale Y₂O₃ particles exhibit remarkable high-temperature properties, which are anticipated to further enhance the service temperature of TiAl alloys and expand their application at elevated temperatures.