Fragmentation and refinement behavior and underlying thermodynamic mechanism of WC reinforcement during selective laser melting of Ni-based composites

Abstract

The WC-reinforced Inconel 718 composites were successfully fabricated through selective laser melting (SLM) additive manufacturing technology. Influences of the applied laser energy densities on the thermodynamics within the molten pool, fragmentation behavior of WC particles, and underlying fragmentation mechanism were investigated through experiments and simulations. The results revealed that the fragmentation behavior of WC particles was greatly dependent on the applied laser energy input. As a relatively low laser energy density was applied, the alloyed reaction layer formed around WC particles, and then experienced a fragmentation into a certain number of carbides in the vicinity of WC particles, due to the temperature gradient and resultant thermal tensile stress exerted at the interface of WC particles and molten Inconel 718 alloy. This fragmentation of WC particle was defined as the dissolution-diffusion-fragmentation mechanism. For an elevated laser energy density of 330 J/m was used, an increased temperature gradient and attendant thermal stress formed, and the initially incorporated WC particles experienced a severe heat damage, thereby directly fragmenting the WC particles into the refined pieces. Meanwhile, the molten liquid with more intense thermal convections favored the homogeneous distribution of the broken WC particles and the formation of the alloyed reaction layer between WC particles and molten Inconel 718 alloy liquid, which was predominated by the fragmentation-dissolution-diffusion mechanism.