时效处理对Ti55531钛合金微观组织演变规律及力学性能的影响

Effect of Aging Treatment on Microstructure Evolution and Tensile Properties of Ti55531 Titanium Alloy

摘要:

近β型钛合金Ti55531在INSTRON-5948R微型材料试验机上开展了经800 ℃/2 h固溶+580~640 ℃/6~10 h时效热处理后的力学性能试验,获得了不同时效工艺下Ti55531合金的力学性能及强塑积。研究了时效处理对合金微观组织演变规律及合金在拉伸变形时的断裂机制。结果表明：次生片层 α 相对时效参数变化比初生 α 相更敏感。次生片层 α 相厚度与时效温度或时效时间呈线性正相关。与时效时间对比可知,次生片层α相粗化速率对时效温度敏感性较弱,且其随时效温度和时效时间粗化速率分别约为1 nm/℃和8 nm/h。合金经固溶时效后,其力学性能显著提升,且合金在800 ℃/2 h固溶+640 ℃/8 h时效后达到最佳的综合力学性能,此时抗拉强度为1144 MPa,延伸率为8.16%,且强塑积超过9.3 GPa.%。合金经固溶时效热处理后拉伸断裂形式为韧脆混合型断裂,且以韧性断裂为主,包括晶间开裂和微孔合并。

Abstract:

The mechanical property tests of near β-type Ti55531 titanium alloy after solution (820 _^oC/2 h) plus aging (580~640 _^oC/6~10 h) treatments were carried out on INSTRON-5948R micro tensile machine. The effects of solution plus aging treatment on microstructural evolution and mechanical properties of Ti55531 alloy were studied to obtain a better combination of ultimate tensile strength and ductility. Furthermore, the fracture mechanism of the alloy during tensile test was discussed. The results show that the secondary lamellar α phase is more sensitive to the change of aging parameters than the primary α phase. and the thickness of lamellar α phase is linearly positively correlated with aging temperature or time. Compared with aging time, the coarsening rate of the secondary lamellar α phase is less sensitive to aging temperature, and the coarsening rate of the secondary lamellar α phase with aging temperature and aging time is about 1 nm/oC and 8 nm/h, respectively. After solution and aging treatment, the mechanical properties of Ti55531 alloy are significantly improved, which reach the best comprehensive mechanical properties with solution treatment at 800 _^oC for 2 h plus aging at 640 _^oC for 8 h. Under this condition, the ultimate strength is 1144 MPa, the elongation is 8.16%, and the strength-ductility product exceeds 9.3 GPa .%. The tensile fracture modes of Ti55531 alloy are ductile and brittle mixed fracture, and mainly ductile fracture, including intergranular cracking and microvoid coalescence mechanisms.