Evaluation of braze bonded hard complex boride based coatings for sliding, erosion and abrasion wear

Materials requiring improved resistance to wear have been researched in coatings as well as in bulk form. A new process that aims to produce a wear resistant surface through powder metallurgy exists. The process brazes a green tape containing a reactive mixture of Mo, Fe, Cr, MoB and FeB and which produces a microstructure of hard complex borides dispersed in a soft metallic matrix, onto a compatible metallic substrate. Hence the process is called as “Braze-bonding”. In the process the phenomena of coating densification, microstructure development and interface development occur simultaneously. The resultant hard layer is evaluated for performance under sliding wear, erosive wear and abrasive wear conditions. It has been found that the coating is competitive to other hard materials. The process has inherent advantages like applying the coating in situ and easily allows for varying the thickness of the coated layer. A diffusion driven interface between coating and substrate improves bond strength. Complex borides of more than 50 vol.% dispersed in a Fe based ductile matrix help in abating wear through different mechanisms, which have been discussed here. The braze coatings can be used for applications involving wear resistance like pump impeller parts, machining tools, and injection molding screws.