固溶时效处理对TC20钛合金α相演变和硬度的影响

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

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。

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,andβ→αphase transformation of TC20 alloy duringαrelative aging was studied.The results show that the hot rolled microstructure is composed ofαandβphase,and many smallαphases are formed in the solid solution structure.The lamellar-distributedαphase in the specimen is formed at 460℃for 4 h,and theαphase 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 fineαphases is close to 100 nm.The second phase formed by the two aging methods isαphase,and theαphase with smaller size is obtained at 320℃for 15 min→460℃for 4 h.When the temperature reaches 460℃,a multitude ofαphase nucleated in theβmatrix can be carried out byωphase,thus formed a dense and uniform distribution.Theωphase in the alloy is no longer exists after 320℃for 15 min→460℃for 4 h treatment,and moreαphase is precipitated at the same time.The alloy hardness is up to 503 HV,which is significantly higher than that ofβmatrix,and the hardness of the alloy can be improved by the precipitation ofαphase substantially.