Microstructural characterization and enhancement of the wear behaviour of 316L+WC Metal Matrix Composite processed by Directed Energy Deposition

Additive manufacturing (AM), and in the particular laser cladding (LC), is a suitable technique for the manufacturing of composite coatings, allowing for a large variability in raw materials. In laser cladding, a stream of a powder, or a mixture of different powders, is fed into a focused laser beam while being scanned across a substrate, thus leaving behind a coating or object. Laser cladding process involves ultra-fast cooling rates during the solidification stage and the subsequent solid state transformations, thus giving rise to out-of-equilibrium phases.
Austenitic stainless steels (e.g. SS316L) are widely used due to their corrosion resistance and good toughness. However, their applications are still limited by their relatively poor tribological properties at high temperature. Surface damage occurs in areas under contact loadings. A composite coating or thick deposit in those zones appears as an interesting solution, combining the matrix material with WC hard reinforcements. Possible reinforcements require high hardness, chemical affinity and theoretical high
melting temperature of 2200℃. Moreover, a particularly interesting field is the conception of new alloys modifying the liquid composition and solidification route by interaction between reinforcements and melt pool during deposition.
In the present work a metal matrix composite (MMC) composed by 316L stainless steel and WC reinforcements is considered. The aim is understanding the effect of WC reinforcements on an austenitic microstructure obtained by LC, in order to being applied to much harder matrix in future works. Relevant results obtained on the fabricated MMC are discussed restoring the solidification which took place during LC, using a combination of reverse DTA analysis and microscopy characterization. Moreover, wear tests were carried out on both MMC and 316L cladded materials to show the improvements of
reinforcements on the tribological properties.