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

Chromium Carbide/Nickel-Chrome is a good wear resistant coating at elevated temperatures up to 850 degreesC. High velocity oxy-fuel (HVOF) is a promis ing process for preparation of the CrC/NiCr coatings. During thermal spray process, the speed and surface temperature of in-flight molten particles ar e 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 pro cess parameters on molten particle speed and surface temperature, and the p roperties of prepared CrC/NiCr coatings were subjected to a DOE investigati on. According to the experimental results, the major control factors affect ing particle temperature are powder feed rate, stand-off distance and gun b arrel length. Stand-off distance and oxygen flow rate are major factors aff ecting particle speed. Based on the evaluated specimens, porosity contents of all the prepared coatings are less than one percent, and coatings deposi ted by molten particles heated to range of 1650 degreesC-1725 degreesC show ed relatively lower porosity contents. Coatings deposited by higher particl e speed exhibited relatively better abrasion-wear resistance. (C) 2000 Else vier Science B.V. All rights reserved.