Effects of process parameters on molten particle speed and surface temperature and the properties of HVOF CrC/NiCr coatings

Chromium Carbide/Nickel-Chrome is a good wear resistant coating at elevated temperatures up to 850°C. High velocity oxy-fuel (HVOF) is a promising process for preparation of the CrC/NiCr coatings. During thermal spray process, the speed and surface temperature of in-flight molten particles are two key factors affecting the sprayed coating quality. Coating deposited by higher kinetic energy and adequate surface temperature molten particles is expected to be dense and hard. In this study, the influences of HVOF process parameters on molten particle speed and surface temperature, and the properties of prepared CrC/NiCr coatings were subjected to a DOE investigation. According to the experimental results, the major control factors affecting particle temperature are powder feed rate, stand-off distance and gun barrel length. Stand-off distance and oxygen flow rate are major factors affecting particle speed. Based on the evaluated specimens, porosity contents of all the prepared coatings are less than one percent, and coatings deposited by molten particles heated to range of 1650°C–1725°C showed relatively lower porosity contents. Coatings deposited by higher particle speed exhibited relatively better abrasion-wear resistance.