On the effect of laser powder-bed fusion process parameters on quasi-static and fatigue behaviour of Hastelloy X: A microstructure/defect interaction study

The mechanical performance of parts, made by laser powder-bed fusion (LPBF), under quasi-static and cyclic loadings can be altered significantly by changing the process parameters. To better understand the related changes, tensile and fatigue LPBF Hastelloy X coupons were manufactured at high and low laser scanning speeds (LSS) in the nearly full-dense processing window. The experimental results demonstrate that, although the microstructure and surface roughness of the parts varies by altering the LSS, the porosity or density of the printed samples are not changing significantly within the range studied here. High LSS samples show higher tensile strength and higher rates for strain hardening at the primary stages of the deformation. Statistical analysis of variance indicates that LSS is a significant factor affecting the fatigue life. The S-N diagram shows Basquin lines intersection at the midlife fatigue region. In the low cycle fatigue (LCF) region high LSS samples show higher cycles to failures due to hysteresis stabilization at lower strains and hence less relative pre-strain and cyclic damage. Since stress risers are important features at high cycle fatigue (HCF) due to stress concentration and associated plasticity, the low LSS samples tolerate a greater number of cycles at lower stress levels and show a higher fatigue limit obtained by the step-loading method. These findings suggest that the process parameters can be optimized to achieve the best possible performance based on the desired application in LCF or HCF for AM parts.