Effect of spattering on formation mechanisms of metal matrix composites in laser powder bed fusion

Abstract

Metal matrix composites (MMCs) with specially designed structures can be fabricated by laser powder bed fusion (LPBF) time-efficiently and cost-effectively, but reinforcements pose enormous challenges to the technique. In this work, the effect of reinforcement on the formation of MMCs in LPBF is studied by taking diamond grinding wheels (GWs) as an example. Based on the balling phenomenon observed in the LPBF process, the formation characteristics of GWs such as surface morphology, porosity, and flexural strength are investigated. The balling size is increased with an increase in the linear energy density of the laser beam due to more intense diamond spattering. The acting forces applied by the plume and ambient gas flow generated around the melt pool on a diamond grain are analyzed to investigate the generation of diamond spatter. For MMCs with coarse reinforcements, spattering is the dominant cause of the balling phenomenon due to the induced discontinuous melt tracks and uneven powder layers. Furthermore, the performance of a cup-type diamond GW fabricated by LPBF in the electrical discharge grinding (EDG) process of reaction-bond silicon carbide (RB-SiC) is evaluated by the surface and subsurface quality. The grinding process removes the resolidified layer of RB-SiC induced during the electrical discharging process and suppresses crack generation in the subsurface. The results presented in this study reveal the influence of diamond grains on the formation mechanism of GWs, which is also suitable for MMCs with coarse reinforcements.