Ti-55531钛合金室温强-塑-韧匹配化热处理工艺研究

Investigation into the Heat Treatment Technology to Enhance the Compatibility among the Tensile Strength,Ductility,and Fracture Toughness of Ti-55531 Alloy

目的采用Ti-5Al-5Mo-5V-3Cr-1Zr(Ti-55531)钛合金,研究了不同热处理工艺条件下室温强-塑-韧性能的匹配关系,为满足不同强度、断裂延伸率、断裂韧度综合服役性能要求提供热处理工艺参考。方法在单相区固溶+时效、双相区固溶+时效2种制度下进行了热处理试验,分析了不同单相区固溶冷却方式(空冷、炉冷)和时效温度、双相区固溶温度等条件下的室温拉伸性能(抗拉强度σb、断裂延伸率A)和断裂韧度KIC,揭示了Ti-55531钛合金室温强度、塑性、断裂韧度的匹配关系。结果经单相区固溶+空冷+时效处理得到了细片层状次生αs相,随时效温度的升高,αs相尺寸增大,抗拉强度降低,延伸率和断裂韧度升高;经单相区固溶+炉冷+时效处理得到了较粗的α片层,随时效温度从500℃升高至600℃,α片层尺寸增大,抗拉强度降低,延伸率和断裂韧度升高,但呈现出较高的脆性;随着双相区固溶温度的升高,初生αp相尺寸显著降低,促进后续时效处理过程中析出了更细小的次生αs相,提高了强度,降低了延伸率和断裂韧度。结论得到了2种能够实现良好强-塑-韧性能匹配的热处理工艺路线:1)850℃/1 h固溶后炉冷至600℃保温8 h,可得到片层组织以及较高的断裂韧度(KIC=110.01 MPa·m1/2)、良好的强度(σb=1111 MPa)和断裂延伸率(A=9.69%);2)810℃固溶+空冷+600℃/3 h时效,可得到初生αp+次生αs相的双态组织,实现了高强度(σb=1287MPa)和高断裂延伸率(A=12.76%),同时断裂韧度达到60.4MPa·m1/2。

The work aims to take Ti-5Al-5Mo-5V-3Cr-1Zr(Ti-55531)alloy as the object to study the compatibility among the tensile strength,ductility and fracture toughness at room temperature under different heat treatment conditions,so as to pro-vide a reference for heat treatment process to meet the comprehensive service performance requirements of different strength,elongation at break and fracture toughness.Heat treatment experiments were carried out in two systems:βsolid-solution+aging andα+βsolid-solution+aging.Tensile properties(including the ultimate tensile strengthσb,fracture elongation A)and fracture toughness KIC under the conditions of differentβsolid-solution cooling modes(air cooling and furnace cooling),aging tempera-ture andα+βsolid-solution temperature,etc.were analyzed and the compatibility among the tensile strength,ductility and frac-ture toughness of Ti-55531 alloy at room temperature was revealed.Βsolid-solution followed by air cooling and aging treatment resulted in the formation of fine secondaryαlamellar(αs).Theαs size increased with the elevation in aging temperature,causing the deterioration inσb and improvement in A and KIC.Theβsolid-solution followed by furnace cooling and aging treatment produced coarserαlamellar.Elevations in aging temperature from 500℃to 600℃resulted in the rising ofαlamellar size and associated decrement inσb and increment in A and KIC.However,these microstructures exhibited high brittleness(A<3%).In-creasing theα+βsolid-solution temperature reduced the size of primaryαparticles(αp),thus promoting the precipitation of finerαs during subsequent aging treatment and also resulting in the enhancement inσb and decrement in KIC and A.2 heat treatment processes that can achieve good compatibility among the tensile strength,ductility and fracture toughness are obtained:1)After a solution treatment of 850℃/1 h followed by furnace cooling to 600℃and isothermally holding for 8 h,high KIC=110.01 MPa·m1/2 and moderateσb and A are obtained(σb=1111 MPa,A=9.69%).2)After a solid solution treatment under 810℃for 1 h followed by air cooling and aging treatment under 600℃for 3 h,binary structure of primaryαp+secondaryαs phases can be obtained and higher compatibility ofσb and A(σb=1287 MPa,A=12.76%)is obtained.Meanwhile,the fracture toughness is moderate(KIC=60.4 MPa·m1/2),as remarkably lower than that for the lamellar microstructure.