Study on the Microstructure and Properties of Ti650 Titanium Alloy with Thermal Exposure at 650 °C

Abstract:

Ti650 alloy was heat treated at 1005 ℃/1.5 h/air cooling (AC)+660 ℃/2.5 h/AC, followed by thermal exposure test and room temperature tensile test to study its thermal stability. The results show that the highest ultimate tensile strength (UTS) of the alloy after heat treatment is provided by the fine lamellar structure without the participation of precipitated phase. When the thermal exposure time is 100–200 h, the silicide precipitates steadily and no longer grow, and the α₂ phase grows with the increase in thermal exposure time. At 200 h, the α₂ phase reaches the critical size of 6 nm, which has the greatest strengthening effect on the alloy. At this time, the UTS of the alloy, which is increased by the second phase obstructing the dislocation motion, is greater than that which decreases when the layer of α_s phase thickens, resulting in the increase in UTS of the alloy. From 200 h to 500 h, the α₂ phase in the alloy continues to grow, and the dislocation transitions from cutting through the secondary phase to bypassing the secondary phase (the formation of dislocation rings), and the UTS of the alloy gradually decreases.