Optimization of the Flame-Spraying Process and Improvement of Properties of a NiCrBSi Coating by Heat Treatment

The paper describes a study of adhesion strength of wear and corrosion resistant NiCrBSi coatings produced under different flame-spraying conditions on mild steel with 0.08 % carbon. Flame-sprayed coatings often show weak bonding strength to the substrate concerned; therefore, usability of a machine component treated in this way is limited only in case of lower mechanical loads on flame-spray coated parts, and at the same time it is subjected to wear and chemical influences. In order to measure adhesive strength of coatings, the standardized tensile adhesive test (TAT) was used. A Taguchi method was used to perform experiments and analyse results to find the most favourable combination of spraying parameters, i.e. surface roughness, preheat temperature, spraying distance, and type of oxy-acetylene flame, to provide a high-quality adhesive strenght with the substrate. Subsequent heat treatment of the NiCrBSi coating showed significant adhesion strength increase and improvement of microstructural properties.