Microstructural And Thermal Characterization Of 316l+Wc Composite Coatings Obtained By Laser Cladding

Herein, a metal matrix composite (MMC) composed of 316L stainless steel and 20% in volume of tungsten carbides (WC), fabricated by laser cladding (LC) is considered. LC is an additive manufacturing technique, characterized by ultrafast cooling rates and limited diffusion, thus giving rise to out-of-equilibrium microstructures. The microstructure of the MMC is found to consist of partially dissolved WC well distributed in an austenitic matrix reinforced by a network of reaction carbides. Those mixed reaction carbides are formed from a liquid enriched in W and C due to the dissolution of the original WC in contact with the molten metal during deposition. Distribution, chemical composition, crystallographic features, and stability of the different phases are characterized in details by combining electron microscopy, electron backscattered diffraction, and dilatometry. This combination of techniques allows to distinguish among M6C, M23C6, M4C, and WC(1-x)carbide, belonging to the Fe-W-C system and all exhibiting a face-centered cubic lattice. Moreover, results of reverse thermal analyses are considered together with microstructural data to elucidate the genesis of this complex microstructure, differentiating the phases formed in the melt pool, in the vicinity of partially dissolved WC and in the heat-affected zone between two successive tracks.