Laser powder deposition of WC particle reinforced metal matrix composites

Laser Powder Deposition (LPD) is an additive layered manufacturing process that can deposit nearnet shape parts directly from metal powder. Metal Matrix Composites (MMCs) combine the merits of ductile metal matrix and hard ceramic reinforcement, providing enhanced properties including hardness and wear resistance. MMCs can be easily implemented in LPD process via blending the powders during deposition of coatings and 3-D parts. However, cracks induced by thermal stress and material embrittlement limit the application of MMCs in direct LPD processes. This study experimentally investigated the mechanical properties of MMCs deposited via LPD. Hardfacing alloy Stellite 6 and ductile alloy Inconel 718 were chosen as the matrix material, respectively, with spherical Tungsten carbide (WC) particles as the reinforcement. According to the experiment results, Inconel 718 was found to be a better choice for matrix material as it presented better compatibility with WC particles with acceptable wear resistance. Influence of direct age heat treatment of Inconel 718 matrix on mechanical properties was also investigated. Tensile tests showed that addition of WC particles in the matrix reduces both the ultimate strength and elongation. Microstructural observation of the tensile specimens indicated that WC particles are the preferable crack initiation sites, which significantly reduces the load-carrying capacity and ductility of the composite. Dissolution of WC into the matrix, which embrittles the matrix and further reduces the ductility of the composite, was proven by micro-hardness test and elemental analysis. Last, drying sliding test is conducted to evaluate the wear resistance of the MMCs. It was found that a small addition of WC particles can significantly increase the wear resistance.