缺陷对选区激光熔化Ti6Al4V合金高周疲劳性能的影响

Effect of defects on high cycle fatigue property of Selected Laser melting Ti6Al4V alloy

摘要:

明确缺陷对选区激光熔化Ti6Al4V合金的疲劳性能影响规律是突破该材料工程应用瓶颈的关键问题。在缺陷无法避免的工艺背景下，借助于金相显微镜、电子背散射衍射技术、X射线三维成像系统、疲劳试验机、扫描电子显微镜及激光共聚焦显微镜，开展了该材料的组织和缺陷表征，高周疲劳性能及失效机制的研究工作。结果表明，该合金的微观组织表现出增材制造材料独特的工艺特征；材料的致密度为99.99%，整体缺陷尺寸小于60 μm；材料的疲劳极限为398 MPa，断裂试样均在未熔合缺陷处形成疲劳裂纹，且循环周次低于106 cycles。而缺陷处有效应力强度因子大多分布于短裂纹疲劳裂纹扩展门槛值之上，这决定了该材料的循环寿命较低的特点，后续引入K-T模型建立了关于该材料安全服役的评价方法。

Abstract:

It is of significant importance to understand the influence of defects on the fatigue property of Ti6Al4V alloy prepared by selective laser melting for breaking through the limitation of this material in industrial applications. As the defects cannot be completely avoided, with the help of metallographic microscope, electron backscatter diffraction, X-ray tomography, fatigue testing machine, scanning electron microscope and laser confocal microscope, the microstructure and defect characterizations, high cycle fatigue performance and failure mechanism of the material were studied. The results show that, the microstructure of the alloy exhibits the unique process characteristics of additive manufacturing materials. Specifically, the density of the material is 99.99%, and the overall defect size is less than 60 μm. The fatigue limit of the material is 398 MPa, fatigue cracks are formed in the lack of fusion defects of the fracture specimens and the cycles are less than 106. Most of the effective stress intensity factors at the defects of the fractured samples are distributed above the threshold value of short crack fatigue crack growth, which determines the low cycle life of the material. Finally, the K-T model is also introduced to establish an evaluation method for the safe service of the material.