Selective Laser Melting to Manufacture "In Situ" Metal Matrix Composites: A Review

After a brief introduction on selective laser melting (SLM) and ex situ manufacture of metal matrix composites (MMCs), this paper reviews the capacities and benefits of SLM to activate and control various in situ reactions during fabrication of 3D parts. It introduces several systems (such as Al/Fe2O3, AlSi10Mg/SiC, Al/ZnO, Ti/C, Ti/SiC, Ti/Si3N4, Ti/Mo2C, Fe/SiC, etc.) used to manufacture Al-based, Ti-based, and steel-based in situ MMCs. Then, it illustrates the novel microstructural characteristics of these SLM-made in situ MMCs for different cases, as they may appear from nano-particles to nano-whiskers and dendritic reinforcements homogeneously distributed in a metal matrix. It also focuses on SLM associated in situ mechanisms, explaining how an in situ reaction propagates based on decomposition, diffusion, and reformation and how the growth mechanisms turn into different morphologies such as rounded particles, whiskers, or polygonal block shapes. The influence of various SLM parameters (such as energy density, laser power/speed, powder layer thickness, and the size of initial powder particles) and the SLM in situ challenges are also discussed.