4-POINT BENDING TESTS OF THERMALLY PRODUC ED WC-CO COATINGS

The use of hard coatings is limited by their brittleness and cracking when they are submitted to loading. In this study, a four-point bend t est combined with acoustic emission measurements was used to measure t he curvature when WC-Co plasma (atmospheric plasma sprayed) and HVOF ( high velocity oxy fuel) sprayed coatings break. The coatings were depo sited onto a 30NCD16 beam of rectangular cross-section. The heterogene ous beams were tested with the coating in tension. The APS and HVOF co atings are compared. The influence of the state of the surface before spraying and the influence of a post-heat treatment were studied. The role of residual stresses determined by a step-by-step hole drilling m ethod, is also discussed. The results presented show the capacity of t he four-point bend test to characterize the toughness of a coating on its substrate.