Quality Improvement of Flame Sprayed, Heat Treated, and Remelted NiCrBSi Coatings

In this study, properties of NiCrBSi coatings, produced by a two-step process of flame deposition and furnace posttreatment, are analyzed. Adhesion strength, microstructure, porosity, microhardness, chemical composition, and residual stresses were analyzed after deposition and after heat treatment; that is, remelting. Numerous specimens were made to study the adhesion strength of coatings after flame deposition. The four chosen influential factors, that is, surface roughness, preheat temperature of the substrate, distance of flame torch, and type of oxyacetylene flame, were optimized to maximize the adhesion strength, using the Taguchi parametric method. The confirmation experiment showed that the developed experimental model is suitable for optimization of flame spraying deposition process. Based on the evaluation of coating properties, the best overall quality was obtained after remelting at a peak temperature 1080 °C with 5 minutes of holding time, followed by slow air cooling.