TC32钛合金不同热处理工艺下的组织性能及断裂机制

Microstructure, mechanical properties and fracture mechanism of TC32 titanium alloy with different heat treatment processes

以新型高性能低成本TC32钛合金为研究对象,通过光学显微镜、扫描电镜、透射电镜和拉伸试验机等,研究了普通退火(700℃×2 h,AC)和双重退火(880℃×2 h,AC+550℃×6 h,AC)两种热处理工艺对该合金显微组织和力学性能的影响。结果表明:普通退火后,TC32合金组织中初生α相含量约为37.2%,并产生轻微球化现象,β转变基体由较粗片层状的次生α相和残余β相组成,合金的抗拉强度均值为939 MPa,伸长率均值达17.4%;双重退火后,TC32合金组织中初生α相含量约为11.8%,并产生明显的球化现象,β转变基体由网篮状结构的细片层次生α相组成,合金的抗拉强度均值达1258 MPa,伸长率均值为9.4%;两种工艺下合金的室温拉伸断口均表现为韧性断裂,普通退火的断口中纤维区面积和剪切唇面积大,无明显放射区,韧窝数量多、尺寸大、深度深,双重退火的断口中有一定面积的放射区,除了等轴韧窝外,还有一定数量的撕裂棱。

Effect of two heat treatment processes,which were normal annealed(700℃for 2 h,AC)and double annealed(880℃for 2 h,AC and 550℃for 6 h,AC),on microstructure and mechanical properties of the new high-performance and low-cost TC32 titanium alloy was studied by using optical microscope(OM),scanning electron microscope(SEM),transmission electron microscope(TEM),and tensile testing machine.The results show that after normal annealing,the content of primaryαphase is about 37.2%,and a slight spheroidization occurres,theβ-transformed matrix is composed of coarser lamellar secondaryαphase and residualβphase.The average ultimate strength(UTS)under this process is 939 MPa,and the average elongation(EL)is 17.4%.After double annealing,volume fraction of primaryαphase which occurred recrystallization is about 11.8%,andβ-transformed matrix is composed of fine lamellar secondaryαphase with weaving basket-weave structures.The average ultimate strength(UTS)under this process is 1258 MPa,and the average elongation(EL)is 9.4%.Fracture morphologies show that the tensile fracture mechanism of both processes belongs to ductile fracture.The fracture characteristics of normal annealed have larger fibrous and shear lip zones,no obvious radical zone,and more equiaxed dimples with larger in size and deeper in depth.The fracture characteristics of double annealed have a certain area of radical zone,in addition to the equiaxed dimples,a number of tearing edges is observed.