Understanding tensile and creep properties of WC reinforced nickel-based composites fabricated by selective laser melting

In this study, submicron-WC reinforced Inconel 718 composites were fabricated by selective laser melting (SLM). They were investigated regarding forming quality, microstructure evolution, tensile and creep properties. The results demonstrated that SLM-processing with decreasing volumetric energy density (Ed), entailed the fabrication of composites with also decreasing density, due to the formation of more pores and cracks. The microstructure of the prepared composites mainly consisted of two different types, namely cellular and columnar dendrites, which formed within the molten pool. The microstructure was more heterogeneous at smaller length scale, whereby reduced grain size and enhanced high angle grain boundaries (HAGBs) were observed. At the optimal Ed of 120 J/mm3, the SLM-fabricated composite was highly dense and exhibited small stress concentration, so that it showed the highest microhardness (361.7 HV0.2), ultimate tensile strength (1030.5 MPa) and elongation (24.8%). Owing to elongated grain boundaries, which were characteristic for the respective microstructure, the composite displayed reduced creep life and ductility. The deformation behaviors during tension and creep were analyzed and they were interrelated to the microstructural defects, grain size, grain boundary morphology, and dislocation density.