固溶时效处理对TC20钛合金α相演变和硬度的影响

采用SEM、TEM、XRD和硬度等技术对先固溶(840 ℃×0.5 h)后不同时效(460 ℃×4 h;320 ℃×15 min→460 ℃×4 h;320 ℃×10 min;460 ℃×10 min)热处理工艺的TC20合金试样进行了观察与表征,研究TC20合金的α相对时效过程中β→α相转变。结果表明:热轧态组织由α相与β相共同组成,固溶态组织相中生成了许多小尺寸α相。采用460 ℃×4 h进行处理试样内形成了片状分布的α相,采用320 ℃×15 min→460 ℃× 4 h处理试样内形成了具有更小长宽比的α相,并且该试样内的大部分α相尺寸均接近100 nm。两种时效方法形成的第二相都是α相,采用320 ℃×15 min→460 ℃×4 h处理具有尺寸更加细小的α相。当温度到达460 ℃时更多α相可以通过ω相进行形核,从而在β基体上形成致密均匀分布状态。采用320 ℃×15 min→460 ℃×4 h处理后合金中的ω相已不存在,同时析出了更多的α相,合金硬度高达503 HV,显著高于β基体的硬度,α相可以促进合金硬度的大幅提升。

Effect of solid solution and aging on α-phase microstructure evolution and hardness of TC20 titanium alloy

TC20 alloy specimens treated by different heat treatment processes, as well as first initial solution (840 ℃× 0.5 h) and then different aging treatment (460 ℃× 4 h, 320 ℃× 15 min→460 ℃× 4 h, 320 ℃× 10 min, 460 ℃× 10 min) were tested and characterized by SEM, TEM, XRD and hardness tester,and β→αphase transformation of TC20 alloy during α relative aging was studied. The results show that the hot rolled microstructure is composed of α and β phase, and many small α phases are formed in the solid solution structure. The lamellar-distributed α phase in the specimen is formed at 460 ℃ for 4 h, and the α phase with smaller length-width ratio is formed in the specimen when aged at 320 ℃ for 15 min→460 ℃ for 4 h, and most of the size of fine α phases is close to 100 nm. The second phase formed by the two aging methods is α phase, and the α phase with smaller size is obtained at 320 ℃ for 15 min→460 ℃ for 4 h. When the temperature reaches 460 ℃, a multitude of α phase nucleated in the β matrix can be carried out by ω phase, thus formed a dense and uniform distribution. The ω phase in the alloy is no longer exists after 320 ℃ for 15 min→460 ℃ for 4 h treatment, and more α phase is precipitated at the same time. The alloy hardness is up to 503 HV, which is significantly higher than that of β matrix, and the hardness of the alloy can be improved by the precipitation of α phase substantially.