Variation of friction coefficient with percentage of metallic matrix in WC–Co coatings sprayed by HVOF

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Abstract
Hardmetal (WC–Co) coatings are widely used in industry for their good resistance to wear. The continuous improvement of these materials has producedvarious commercial coatings of different metallic matrix content. In the present work, the factors that affect the friction coefficient of HVOF sprayed coatings of WC–12Co and WC-17Co have been evaluated, as have the wear mechanisms taking place during wear testing. By modifying the spraying distance, the two powders were used to produce different coatings in order to study the changes produced on the friction coefficient. A ball on disc test was used to evaluate the specimens (ASTM Standard G99–90) and the resultant structures were observed using optical and scanning electron microscopy. Energy dispersive spectrometrywas used to analyse the wear products generated during testing. The WC–17 Co coatings exhibited higher friction coefficients than WC–12Co coatings. This behaviour was attributed to the larger amount of metallic matrix present. The wear mechanisms were identified as plastic deformation and adhesive wear.

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