等离子弧熔丝增材制造TC4-DT钛合金组织与疲劳断裂行为

Microstructure and Fatigue Fracture Behavior of TC4-DT Titanium Alloy by Plasma Arc and Wire Additive Manufacturing

采用单轴拉伸疲劳试验系统,研究了等离子弧熔丝加微挤压增材制造TC4-DT钛合金的微观组织与疲劳性能关系。结果表明,等离子弧熔丝微铸锻制备的钛合金中原β晶粒呈等轴状,晶内α片状组织与晶间β相形成网篮组织与束域组织,α片层基体有少量位错,及纳米尺寸β相。合金的屈服强度为845.08 MPa,抗拉强度为943.19 MPa,伸长率为14.4%,循环应力比为0.1,频率为25 Hz。随应力幅的增大,合金疲劳寿命降低显著。由于孔洞等缺陷的存在,疲劳寿命出现较大的弥散性。疲劳裂纹萌生于合金内部气孔与未熔合区,疲劳裂纹扩展区有二次裂纹与疲劳辉纹,瞬断区呈韧性断裂特征。

The relationship between microstructure and fatigue properties of TC4-DT titanium alloy prepared by plasma arc and micro-rolling was investigated through uniaxial tensile fatigue test system.The results indicate that the primaryβgrains in the titanium alloy present isoaxial,and the basket-weave microstructure and domain microstructure are generated from intragranularαlamellar structure and intergranularβphase.A small number of dislocation and nanosizedβphase are observed inαlamellar matrix.The yields strength,tensile strength and elongation of the alloy reach up to 845.08 MPa,943.19 MPa and 14.4%,respectively,with the cyclic stress ratio of 0.1 and frequency of 25 Hz.The fatigue life is significantly decreased with the increase of stress amplitude,which shows great dispersion due to the existence of holes and other defects.The fatigue crack is initiated from pores and unfused zone inside the alloy.Secondary fatigue cracks and fatigue striation exist in the fatigue crack expansion zone,and transient breaking zone is characterized by ductile fracture.