Microstructure and tribology of cold spray additively manufactured multimodal Ni-WC metal matrix composites

Cold spray produces thick and dense deposits that can be applied in additive manufacturing or as a repair to recover damaged components. One potential materials system is WC-reinforced Ni composites, which are known for a combination of high hardness and toughness. WC particle size and distribution are some of the most important variables that impact the mechanical properties and wear resistance. In this study, thick multimodal Ni-24 vol%WC composite coatings were additively manufactured using the cold spray technique. Spherical Ni powder and two types of WC particles, i.e., cast and agglomerated, were used as feedstock materials. The microstructure, porosity, WC distribution, and microhardness of coatings were investigated in comparison with cold-sprayed Ni and Ni-agglomerated WC coatings with similar WC fill ratios. Dry sliding wear of multimodal Ni-WC coatings was studied with a sliding speed of 3 mm/s under normal loads of 5 and 12 N and was then compared to Ni and composite coatings made with only agglomerated WC. Multimodal Ni-WC coatings with an altered distribution of WC particles offered an improvement in friction and wear as compared to Ni-agglomerated WC coatings. Characterization of worn surfaces revealed the formation of tribofilms following compaction of wear debris. A more stable tribofilm that developed to a higher coverage was identified for coatings with multimodal WC particles at both tested loads. However, the protective role of tribofilms was reduced at a higher load, caused by subsurface crack propagation. Subsurface microstructure of worn surfaces that are induced by sliding wear was studied, and a correlation between the mechanical properties and microstructure and wear mechanism of coatings was made. Overall, our findings highlight the potential of cold spray additive manufacturing in producing multimodal Ni-WC composite coatings with enhanced wear resistance.