He Yan, Huang Wei, Guo Weiguo, Li Yanping, Zhao Sihan, Lin Dong
School of Aeronautics, Northwestern Polytechnical University, Xi'an 710072, China.
Materials (Basel). 2023 Jul 19;16(14):5099. doi: 10.3390/ma16145099.
Laser additively manufactured (LAM) Ti-6Al-4V alloy has huge application potential in aerospace structural parts such as turbine blades. However, there are few studies on the fatigue properties of such LAM parts under vibration loading, particularly with regard to anisotropy. In this paper, vibration fatigue properties of LAM Ti-6Al-4V by laser melted deposition were investigated along the transversely deposited (TD) and parallelly deposited (PD) directions. Through the first-order bending vibration experiments, the LAM Ti-6Al-4V alloy exhibits obvious anisotropic fatigue properties and significant dispersion in fracture position. The fracture morphology analysis reveals that the vibration fatigue failure was mainly dominated by process-induced defects and microstructure. The fatigue strength at 10 cycles of the samples with defect-free failure features (DFF) at initiation sites is 470.9 MPa in PD and 434.2 Mpa in TD, while that of the samples with defect-related failure features (DRF) at initiation sites is 364.2 Mpa in PD and 381.0 Mpa in TD. For the DFF group, the fatigue behavior is controlled by the prior β columnar grains with preferential orientation, which leads to enhanced fatigue crack propagation resistance for the PD samples. For the DRF group, which has lower fatigue lives, the fatigue anisotropy strongly depends on the projection area of the lack-of-fusion defects relative to the loading direction, resulting in better fatigue performance for the TD samples.
激光增材制造（LAM）的Ti-6Al-4V合金在涡轮叶片等航空航天结构部件中具有巨大的应用潜力。然而，关于此类LAM部件在振动载荷下的疲劳性能的研究很少，特别是关于各向异性方面。本文研究了通过激光熔敷沉积的LAM Ti-6Al-4V沿横向沉积（TD）和平行沉积（PD）方向的振动疲劳性能。通过一阶弯曲振动实验，LAM Ti-6Al-4V合金表现出明显的各向异性疲劳性能以及断裂位置的显著分散性。断口形貌分析表明，振动疲劳失效主要由工艺诱导缺陷和微观组织主导。在起始部位具有无缺陷失效特征（DFF）的样品在10次循环时的疲劳强度，PD方向为470.9MPa，TD方向为434.2MPa，而在起始部位具有与缺陷相关失效特征（DRF）的样品，PD方向为364.2MPa，TD方向为381.0MPa。对于DFF组，疲劳行为由具有优先取向的原始β柱状晶粒控制，这导致PD样品的疲劳裂纹扩展阻力增强。对于疲劳寿命较低的DRF组，疲劳各向异性强烈取决于未熔合缺陷相对于加载方向的投影面积，导致TD样品具有更好的疲劳性能。
