Effect of Flame Spray and Heat Treatment Parameters on Microstructure of Ni-based Coatings

Flame spray is a widely used coating process due to its low cost and wide variety of usable materials. But weak adhesion between splats as well as between coating and substrate and also high amounts of coating porosity are main drawbacks of this technique. To overcome these problems, usually heat treatment process is applied on these coatings. The NiCrBSi coatings which have high wear and corrosion resistance are used at severe tribological conditions. In the present research, Ni-Based NiCrBSicoatings were applied on CK45 steel substrates by flame spray and the effect of spray and heat treatment parameters on their microstructure were studied. The results showed that applied coatings on the sand blasted substrates under the condition of 150 g/min powder feed rate and 15 cm spray distance, have laminar splat microstructure with the lowest amounts of porosity. Also the effect of heat treatment’s temperature and time on the microstructure and generated phases in the coatings was investigated.Phase analysis showed that Ni, CrB, (Cr,Fe)7C3, Ni3B and Ni5Si2 phases are generated in the coatings microstructure which were heat treated at 1075°C. In addition to theses phases, Cr2Ni3B6 phase was also detected in the coatings which were heat treated at 1100°C.