Mechanisms driving high-cycle fatigue life of as-built Inconel 718 processed by laser powder bed fusion
Mechanisms driving high-cycle fatigue life of as-built Inconel 718 processed by laser powder bed fusion
复制标题
DOI：
10.1016/j.msea.2019.06.003
复制
发表时间：
2019-07-22
期刊：
影响因子：
6.4
通讯作者：
Spear, Ashley D.
中科院分区：
文献类型：
--
作者：
Watring, Dillon S.;Carter, Kristen C.;Spear, Ashley D.
本研究调查了高周疲劳寿命，表面粗糙度和增材制造工艺参数之间的关系，在激光粉末床融合Inconel 718在建成条件。通过改变激光功率、扫描速度、层厚度和构建方向，使用25组不同的处理参数制造标准化疲劳样本，每个参数组重复三个样本。使用白色光干涉法进行表面粗糙度测量;测量高周疲劳寿命;使用扫描电子显微镜进行断口分析。观察到两个工艺参数指标主导高周疲劳寿命：构建方向和激光能量密度。由于构建方向和表面粗糙度之间的关系，构建方向影响疲劳寿命。增加表面粗糙度降低了疲劳寿命，由于增加了表面裂纹萌生位点的数量。对于固定的构建方向，超出最佳范围的激光能量密度会因次表面缺陷而降低疲劳寿命。具体而言，断口分析表明，在低激光能量密度和二次开裂和孔隙（可能与锁眼）在高激光能量密度的次表面缺陷包括缺乏offshore孔。虽然试样之间的残余应力的变化也可以发挥作用，这项工作的重点是几何表面和次表面缺陷所造成的不同的工艺参数及其相应的影响，总的疲劳寿命。基于这些发现，提供了提高增材制造的Inconel 718在完工，非热处理条件下的疲劳寿命的指南。
This study investigates the relationships among the high-cycle fatigue life, surface roughness, and additive manufacturing processing parameters in laser powder bed fusion Inconel 718 in the as-built condition. Standardized fatigue specimens were manufactured using 25 different sets of processing parameters by varying laser power, scan speed, layer thickness, and build orientation, with three repeat specimens per parameter set. Surface roughness measurements were conducted using white light interferometry; high-cycle fatigue life was measured; and fractography analysis was performed using scanning electron microscopy. Two processing-parameter metrics were observed to dominate high-cycle fatigue life: build orientation and laser-energy density. Build orientation affected fatigue life due to the relationship between build orientation and surface roughness. Increasing surface roughness decreased the fatigue life due to increasing number of surface-crack initiation sites. For a fixed build orientation, the laser-energy density, outside of the optimal range, decreased the fatigue life due to sub-surface defects. Specifically, fractography analysis showed that sub-surface defects consisted of lack-offusion pores at low laser-energy densities and secondary cracking and pores (possibly related to keyholing) at high laser-energy densities. While variability in residual stresses among the specimens could also play a role, this work focuses on geometrical surface and sub-surface defects caused by different processing parameters and their corresponding impact on total fatigue life. Based on these findings, guidelines are offered to improve fatigue life of additively manufactured Inconel 718 in the as-built, non-heat-treated condition.