Island scan length effect on processability, microstructure, and mechanical property of laser powder bed fusion processed nickel matrix composites

Nickel matrix composites (NMCs) reinforced with WC particles were manufactured by laser powder bed fusion (LPBF) using island strategy with the variation of island scan length. The processability, microstructural evolution, and mechanical property were investigated. The results indicated that all samples showed high densification, while the surface morphology, molten pool geometry, and microstructures were distinct. With increasing scan length from 0.5 to 1 mm, the grain size was similar, while the high angle grain boundaries (HAGBs) decreased from 68.1% to 50.4%. With further increasing scan length, the residual stress increased from 206.3 to 308.8 MPa, the surface roughness and molten pool configurations were enlarged, and columnar/cellular dendrites became irregular. This change was related to the large temperature gradient and unstable thermal behaviors resulting from the weakened preheat effect under long scan length. Thus, the superior mechanical properties with wear rate of 4.09 × 10−5 mm3/N·m, ultimate tensile strength of 1132 MPa, and elongation of 16.1% were obtained at the moderate scan length of 1 mm. The high performance was related to smaller residual stress, fewer HAGBs and dislocation-carbides interactions along the columnar/cellular boundary.