选区激光熔化TC4钛合金疲劳裂纹扩展行为研究

Research on Fatigue Crack Growth Behaviour of Selective Laser Melted TC4 Titanium Alloy

选区激光熔化增材制造(AM-SLM)技术广泛应用于钛合金结构部件制造。SLM钛合金材料疲劳性能具有明显各向异性。研究SLM钛合金在不同方向载荷下的疲劳裂纹扩展行为对于航空结构耐久性/损伤容限设计具有重要意义。基于此,本文设计了与打印方向呈0°、45°、75°和90°的4种不同取样角度及未处理和热处理的钛合金紧凑拉伸试验件(CT),完成了应力比R=0.1下的疲劳裂纹扩展速率试验,得到了da/d N—ΔK关系曲线,分析研究了取样角度及后处理对疲劳裂纹扩展的影响。结果表明,75°和90°试件的裂纹扩展速率较快,45°试件最慢。45°和75°试件在疲劳试验中会出现裂纹偏转现象,且45°试件疲劳断面沿厚度方向存在较小坡度。经过热处理后,75°试件疲劳裂纹扩展速率显著降低。

Additive manufacturing-selective laser melting(AM-SLM)technique is widely used to manufacture titanium components.Anisotropic fatigue behavior can be observed in SLM titanium materials.It is essential to study fatigue performance of SLM titanium alloy under different loading direction to perform durability and damage tolerance design for aircraft structures.So,four types of compact tension(CT)specimens with 0°,45°,75°and 90°angle to build directions are designed,and two types of post-treatments are chosen.Fatigue crack growth tests at a stress ratio R=0.1 are performed.da/dN-ΔK curves are obtained,and the effects of build direction and post-treatment are analyzed.The result shows that 75°sample and 90°sample have higher fatigue crack rate,while 45°sample has the lowest value.The crack paths of 45°sample and 75°sample deflect with fatigue crack propagating.There is a small slope along the depth in the fracture surface of 45°sample.After post-treatment,fatigue crack growth rate of 75°sample is decreased.