Stainless steel 316L + WC composite coating produced by laser cladding: on the role of particles dissolution and interfacial reactions

Austenitic stainless steels are widely used due to their high corrosion resistance but their relatively poor tribological properties still limit their fields of application. Reinforcing locally the surface of SS316L in areas exposed to sliding contact thus appears as an interesting solution, combining the properties of the matrix with the benefits of harder ceramic materials. As reinforcement, WC is a good candidate due to its hardness and its high melting temperature (2600°C) and the additive process known as laser cladding is well suited for the local deposition of SS316L + WC composite coatings. In this process, a mixture of powders is fed into a focused laser beam, (partially) melted and projected unto a substrate. Laser cladding is characterized by ultra-fast cooling rates during the solidification stage and the subsequent solid state transformations, thus giving rise to out-of-equilibrium phases. When processing a mixture of SS316L and WC powders, in particular, partial dissolution of WC particles in the SS316L melt pool is observed, followed by the precipitation of new reaction products [1].
This study investigates the microstructure of a SS316L – 20 vol% WC composite, focusing on the identification of out-of-equilibrium reaction products resulting from the partial dissolution of the WC particles during laser cladding. To this aim, SEM+EDS observations are combined with electron backscatter diffraction (EBSD) analysis (see figure). Differential thermal analysis (DTA) is also used both on raw powders and on laser clad deposits, to help gain more insights into the solidification and precipitation sequence of the different phases.
1. Mertens, A.; Lecomte-Beckers J. On the Role of Interfacial Reactions, Dissolution and Secondary Precipitation During the Laser Additive Manufacturing of Metal Matrix Composites : A Review. In: New Trends in 3D Printing; 2016:187.