CMT电弧增材制造TC4钛合金的显微组织与力学性能

Microstructure and mechanical properties of CMT wire arc additive manufactured Ti-6Al-4V titanium alloy

采用冷金属过渡(CMT)电弧增材制造技术制备了TC4钛合金样品,测试了沉积态试样的拉伸性能、冲击性能和疲劳性能,讨论电弧增材制造钛合金成形件的疲劳断裂机理。结果表明:经历CMT工艺条件下的快速熔凝过程后,钛合金成形件内宏观组织由外延生长的粗大β柱状晶组成,显微组织为细长α片层和网篮组织。成形件拉伸强度较高,达到锻件拉伸强度水平,但是塑性较低,略低于锻件塑性,且存在一定的各向异性,拉伸断口呈现半解理断裂与半韧性断裂特征。沉积态钛合金成形件具有良好的冲击性能,但冲击性能的各向异性并不显著。钛合金成形件的高周疲劳极限为460 MPa,疲劳源均形核于条状未熔合缺陷及气孔缺陷处。缺陷直径越大,距离表面越近,应力集中现象就越明显,导致样品具有较低的疲劳强度和疲劳寿命。

TC4 titanium alloy samples were fabricated by cold metal transfer wire arc additive manufacturing process(CMT-WAAM). Tensile strength, impact toughness and fatigue resistance of the samples in as-deposited condition were evaluated. The fatigue fracture mechanism of the WAAM-fabricated samples was investigated. The results show that the macrostructure of the as-deposited samples is consists of coarse β columnar crystals grown epitaxially. And the microstructure is composed of α elongated lamellar and basket weave due to low heat input of CMT. The tensile strength is high, reaching the level of forgings, but the plasticity is low, slightly lower than that of forgings, and there is a certain anisotropy. The tensile fracture shows semi-cleavage and semi-ductile fracture.The WAAM-fabricated samples, showing obvious anisotropy, have higher tensile strength and lower plasticity compared with the forgings. The tensile fracture shows a semi-cleavage and semi-ductile fracture mechanism. The as-deposited samples show a good impact ductility, and the anisotropy of impact performance is not significant.The fatigue limit of the as-deposited sample is 460 MPa, and the fatigue crack sources nucleate at strip-shaped incomplete fusion and pore defects. With the increase of the size of defect diameter and decrease of distance between sample surface and defect, stress concentration becomes more critical, which results in a lower fatigue strength and a shorter fatigue life.