The effect of attributes of micro-shapes of laser surface texture on the wettability of WC-CrCo metal ceramic coatings

WC-CoCr coatings sprayed by high velocity oxy fuel (HVOF) are being used for components which are prone to severe erosion or abrasion. In this study, the HVOF coatings were applied to Polycrystalline Diamond Compact (PDC) bits. The HVOF-sprayed WC-CoCr coatings were textured with different structural features by laser surface texturing (LST) technology. The cross-section morphology of the original coating and surface morphologies of textured coatings were observed by scanning electron microscopy (SEM). The contact angles (CA) of deionized water and drilling fluid on the coatings were measured by contact angle analyzer. The results showed that the coatings present a layered structure with a few pores. The original coating exhibits CA of 81.5° with deionized water, and 69.0° with drilling fluid. Nevertheless, the CA of deionized water is 136.5°; and that of drilling fluid is 112.2° on the textured surfaces. The CA keeps rising with the increasing coverage rate R of surface texture corresponding with reducing texture spacing. Surface texture with a grid distance of 100 μm results in the maximum CA on the WC-CoCr coating, due to the co-actions of surface topography and interfacial chemical performances. However, the hydrophobicity of the textured coating is not stable, which may result from the instability of the trapped air on surface textures.