Metallurgical Defects, Microstructure, and Mechanical Properties of ECY768 Alloy Processed via Laser Powder Bed Fusion (Invited)

Laser powder bed fusion (LPBF) is an ideal technique for the comprehensive fabrication of intricate components using cobalt-based superalloys. Despite the outstanding performance of ECY768, a novel cobalt-based superalloy, there exists a research gap concerning the LPBF processing of this alloy. This study delves into the metallurgical defects, microstructure, and fundamental mechanical properties of the ECY768 cobalt-based superalloy when subjected to LPBF. The findings reveal that the predominant metallurgical defects in ECY768 alloy processed by LPBF are gas pores, lack-of-fusion, and hot cracks. Adjusting processing parameters, such as laser energy density, facilitates the production of ECY768 specimens devoid of cracks and exhibiting high density (porosity < 0. 5%). The LPBF-processed ECY768 alloy exhibits a mixed grain structure comprising predominantly columnar grains with some equiaxed grains. A<0 0 1> preferred orientation, nearly parallel to the build direction, is evident. Within the solidification grains, a cellular dendritic microstructure is observable. Sub-grain boundaries concentrate both a dislocation network and two types of nano-scale carbides-ball-shaped MC-type carbides and band-shaped M23C6-type carbides. Under optimized processing parameters, the yield strength of ECY768 specimens reaches 1002 MPa (parallel to build direction) and 1268 MPa (perpendicular to build direction), surpassing that of other main cobalt-based superalloys formed by casting or LPBF. Simultaneously, the elongation of ECY768 specimens is 10. 5% (parallel to build direction) and 13. 3% (perpendicular to build direction), aligning closely with the performance of other main cobalt-based superalloys produced through casting or LPBF. The exceptional mechanical properties of LPBF-processed ECY768 alloy are attributed to satisfactory relative density, a refined cellular dendritic microstructure, substantial nanocarbide precipitation, and their interaction with the dislocation network.