Establishing specimen property to part performance relationships for laser beam powder bed fusion additive manufacturing

Abstract

This study investigates the possibility of correlating specimen property to part performance for laser beam powder bed fusion (LB-PBF) additive manufacturing by altering the process parameters in order to create similar thermal histories experienced during fabrication. In particular, the effects of altering scanning speed on LB-PBF 17-4 precipitation hardening (PH) stainless steel (SS) parts with different geometries on the thermal history, as well as the resultant defect formation, microstructure, and fatigue behavior are studied. It was found that parts with different geometries, all fabricated using the same manufacturer recommended process parameters, exhibited different fatigue strengths, which challenges the specimen property to part performance correlation. Melt pool analysis revealed that altering scanning speed can affect the melt pool characteristics including its depth and overlap depth. Increasing the input energy within the process window, by decreasing the scanning speed during fabrication, was seen to result in deeper melt pools and melt pool overlaps, and consequently, less volumetric defects, specifically lack of fusion, in the material. Therefore, the scanning speed was adjusted for different geometries to result in similar melt pool characteristics, as an indicator of the thermal history experienced during fabrication, which also resulted in these parts having similar porosity. Accordingly, fatigue lives of parts fabricated with adjusted process parameters were observed to be within a similar range. While many other factors may be involved, the findings of this research indicate that maintaining a similar thermal history by altering the process parameters is critical in establishing reliable relationships between specimen property and part performance in additive manufacturing.