Microstructural study of NiCrBSi coatings obtained by different processes

This paper analyses the influence of the processing conditions on the microstructure and wear behaviour of NiCrBSi coatings. Ni-base alloys, which are widely used to obtain wear resistant coatings, are usually heat treated after thermal spraying to improve their tribological properties. Thus, three different processes are studied: flame spraying combined with flame remelting, flame spraying combined with laser remelting, and laser cladding. Comparison of the resulting microstructures, which are observed by scanning electron microscopy (SEM), revealed remarkable differences not only in the morphology but in the size distribution and relative proportions of the observable phases from one coating to another. Notwithstanding this, all the analysed coatings exhibited similar phases in their microstructure. The tribological behaviour of the coatings was compared in room-temperature dry sliding wear tests (block-on-ring configuration), under several load conditions (30, 60 and 90 N). In addition, main wear mechanisms are investigated by characterising the coating wear tracks using SEM. The wear behaviour was very similar for all the coatings tested, although a transition from an oxidative to adhesive wear regime was observed in the range of test carried out.