Effect of Post-Heat Treatment on the Corrosion Resistance of NiWCrBSi HVOF Coatings in Chloride Solution

Abstract

High velocity oxygen fuel (HVOF) thermal spray is one of the most versatile and fastest techniques used to apply wear- and corrosion-resistant coatings to critical component surfaces. In such applications where the material is submitted to a corrosive environment, coating porosity is one of the most important microstructural aspects determining the performance of the material. In the present work, the results regarding the effect of both carburizing flame and argon atmosphere post-heat treatments on the microstructure and corrosion resistance of NiCrWBSi coatings are reported. Both microstructural characterization and porosity determination were carried out before and after the heat treatments. It was determined that both treatments had reduced the porosity considerably, and this reduction was accompanied by pronounced microstructural changes regarding the disappearance of the initial lamellar structure, a more uniform distribution of the hard phases, and a decrease in the number of microcracks and unmelted particles. Results from potentiodynamic studies carried out in a 5% NaCl solution have indicated an increase in the corrosion resistance of both heat-treated coatings.