Characterization of flame sprayed NiCrBSiMo coatings deposited with different spraying parameters

Abstract

Optimization of processing parameters of a Ni-based coating is reported here. Three deposition variables were evaluated, viz. stand-off distance, flame chemistry, and nozzle diameter, on the crystal structure, porosity content, hardness and thickness of the coatings. The analysis was divided into two stages: firstly, the influence of the stand-off distance on the structural and microstructural characteristics of the coatings was determined. In the second stage, a simple 22 factorial design of experiments was employed to investigate the effect of the nozzle diameter and flame chemistry on the porosity, hardness and thickness of the coatings. Results indicated that porosity was strongly influenced by the stand-off distance. Flattening of the particles was achieved at intermediate distance decreasing the porosity; whereas the later increases for short or long distances as a result of the extended or limited particle deformation at impact, respectively. Regarding the nozzle diameter and flame chemistry, results revealed that the former has the predominant effect on the microstructure and hardness of the coatings. Small nozzle diameter and neutral flame reduce the porosity and increase the hardness of the coatings. NiCrBSiMo coatings with low porosity and high hardness using a low-cost thermal spray process are obtained through a parameter optimization.