新型β钛合金的时效机制和相变动力学研究

Aging-Hardening Behavior and Phase Transition Kinetics of a Novel β-Ti Alloy

采用光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)、拉伸实验和硬度测试等分析方法,研究了热轧态新型β钛合金直接时效、固溶时效处理后的组织性能,计算了两种不同热处理制度下合金的等温相变动力学方程。结果表明:随时效时间延长,两种热处理合金的α析出相速度均呈现先快后慢趋势,使得合金硬度增加先快后慢;直接时效和固溶时效的峰值响应时间分别为10和12 h,相应的α析出相平均宽度分别为80和120 nm,合金显微硬度为HV 404和HV 383、抗拉强度为1472.5和1393.6 MPa、延伸率为9.36%和12.56%;峰值响应时间对应的α析出相百分比最大、晶粒细小,合金硬度/强度达到最大;时效时间继续延长出现"过时效",其主要原因是析出相的合并与长大;直接时效的Avrami指数n=1.4885略大于固溶时效的(n=1.4557),这说明两种热处理合金的α析出相形核长大机制相同,但轧态合金更高的位错密度使得直接时效的形核质点更多、时效响应速度更快。

Microstructures, tensile properties and isothermal transformation kinetics of a novel β titanium alloy during direct aging treatment and solution treatment age(STA) treatment were studied through optical microscopy(OM), scanning electron microscopy(SEM), transmission electron microscopy(TEM), tensile test and hardness test. The results showed that the precipitated speed of α phase of the two kinds of heat treatments for the alloy increased fast at the early stage and then it slowed down, resulting in a same trend for the increment of hardness. After direct aging for 10 h or solution treated for 0.5 h plus aging for 12 h(STA treatment), the volume fraction of α phase reached to a peak value, the average width of α grains were 80 and 120 nm, the hardness reached to HV 404 and HV 383, the ultimate tensile strength were 1472.5 and 1393.6 MPa, and the elongation were 9.36% and 12.56%. At this time, the volume fraction of α phase reached to a peak value and the grains were fine enough to get the highest hardness/strength. With aging time increases, the alloy was overheating and the main reason was the growth of α grains. The Avrami index n for direct aging was 1.4885 which was a little higher than that of STA(n=1.4557). It meant that the mechanism of nucleation and growth of the alloy for the two kinds of heat treatments were the same because of the small difference in n, however the nucleation sites for direct aging were more and the precipitation rate was faster.