Characterization and sliding behavior of HFCVD diamond coatings on WC-Co

The effect of three conditioning treatments (scratching, S; scratching and nitric acid etching, SE; scratching, Murakami etching and nitric acid etchi ng, SM) on the properties and dry sliding wear behavior of diamond coatings on WC-Co substrates produced by hot filament CVD was investigated. In spec imen S the critical strain energy G, for coating spallation was found to be similar to the available strain energy due to the residual stresses alone, Go. In the other two specimens, where cobalt was removed from the substrat e surface before coating, G, was found to be 1.1 (specimen SE) and 1.8 (spe cimen SM) times Go. The dry sliding tests against an austenitic stainless s teel counterface revealed, for all the coatings, a high run-in friction coe fficient (about 0.6) followed by a tribological stage characterized by a ve ry low friction coefficient (about 0.05). However, due to the high counterf ace ductility a transfer layer was soon formed, which increased friction co efficient and, thereby, the applied friction stress. In specimens S, this p roduced a rapid removal of the coating by buckling. In the other two specim ens, only localized damage regions were detected, due to buckling for speci men SE and wedging for specimen SM. Additional sliding tests of specimen SM were carried out against an Al alloy counterface, a very soft material, an d a granite, a very hard and brittle material, in order to highlight the in fluence of counterface on the dry sliding behavior of the coating. In the c ase of sliding against the Al alloy counterface, transfer phenomena started immediately after the run-in stage and a tribological stage with a low fri ction coefficient was not observed. In the case of sliding against granite, the friction coefficient continuously decreased during sliding tending to zero. (C) 2001 Elsevier Science B.V. All rights reserved.