"The role of nano-sized WC and TiC powders in microstructure formation and properties of WC-Co coatings"

Properties of WC-Co coatings depend on WC grain size, reactions during spraying, and evolution of the microstructure during formation stage. Among the different strategies to improve WC-Co thermal spray coatings, the use of nano-sized feedstock or, in particular, bimodal ones have been found to be beneficial to mechanical properties. Mixing WC-Co powders or other materials to standard-sized WC-Co could be effective in enhancing wear resistance of thermal sprayed coatings.

In a first group of samples, agglomerated and sintered WC-17Co feedstock powder was mixed with 5wt.% of nano-sized WC(40-70 nm), while a second group was prepared by adding 5wt.% of nano-sized TiC(40-100 nm). The powder mixtures were HVAF sprayed on carbon steel substrate. Different characterization methods were applied to analyze the coatings microstructure:XRD, SEM, STEM+SAED. Dry sliding wear behavior and friction coefficients were evaluated via ball-on-disk wear tests against Al₂O₃ counterparts at the room temperature as well as at 400^oC. The microstructure observations revealed partial dissolution of nano-WC in the coating, whereas nano-TiC remained stable. During the wear tests at room temperature nano-WC slightly decreased friction coefficient and wear rates, but nano-TiC caused an increase of these factors. At 400^oC both nano-sized additions induced decrease of friction coefficient and wear rates.