Characterisation of CoB–Co₂B coatings by the scratch test

New results about the scratch practical adhesion-resistance of the CoB–Co₂B/substrate system developed at the surface of CoCrMo (ASTM-F75) alloy were estimated. The boron diffusion on the surface of the cobalt alloy was conducted using the powder-pack boriding process at temperatures of 1223 and 1273 K with different exposure times for each temperature. The scratch tests over the surface of cobalt borided alloy were performed with a 200 micrometres Rockwell C diamond indenter considering a continuously increasing normal force for the entire set of experimental conditions of the boriding process. The worn tracks produced on the coating/substrate system were analysed by optical and scanning electron microscopy to estimate and identify the critical loads and failure mechanisms, respectively. The results indicated that the critical loads varied between 95 and 142 N as a function of the boride coating thicknesses with a development of various types of failure mechanisms over the surface of the coating/substrate system.