Microstructure and tribological properties of plasma-sprayed WC-17 Co coatings with different carbide grain size distribution

In the present work, three experimental WC-17 Co plasma sprayed coatings were developed from submicrostructured, conventional and bimodal (composing of 30 wt.% submicrostuctured and 70 wt.% conventional WC grain) agglomerated powder. The effect of carbide size distribution on the microstructure, phase structure and properties such as microhardness, fracture toughness and sliding wear performance of three coatings were measured. The experimental results indicated that bimodal coating had little porosity of microstructure with lower degree of decarburization of the WC phase to W2C and Co6W6C phases, consequently, showed both high microhardness and fracture toughness, e.g. the microhardness is similar to that of the submicrostuctured one and the fracture toughness is comparable to that of the conventional one. The coefficient of friction for the coatings decreased slightly with increasing test load, and that friction coefficient of bimodal coating was lower than the other ones. The wear loss of both submicrostuctured and conventional coatings were higher than the bimodal coating and increased with increasing test load. The microscopic analyses of the wear surface showed the cobalt extrusion followed by carbide fracture, or pulled out were the predominant failure mechanism. Besides that, fatigue cracking of the submicrostuctured coating at a high test load played an importance on the wear mechanism.