Abstract
Thermal spray coating applications require precise control of substrate temperature during deposition in order to achieve optimum performance of the final part. Applications such as high-velocity oxy-fuel (HVOF) hardfacing of aircraft landing gear and plasma spraying of thick sputtering targets are but a few examples where control of substrate temperature throughout the entire coating cycle is critical. A broad effort to develop a versatile and cost-effective cryogenic gas cooling system for controlling part temperature in high-energy thermal spray operations is described. Results show that the new liquid nitrogen cooling technology can significantly improve productivity of many conventional operations and provide corresponding powder and process gas savings by completely eliminating the need for interpass cooling breaks. Optimized temperature control and minimization of coating oxidation during the spraying process, resulting from the use of the new system, were also found to: (1) preserve substrate properties, (2) decrease residual stress gradients at coating interfaces, (3) enable applications of soft masking materials, and (4) increase the deposition efficiency (DE) of WC-CoCr coatings while minimizing decarburization of the WC phase. This work focused on HVOF spraying of WC-CoCr coatings which offer a performance and cost alternative to toxic chromium (Cr6+) plating but yet to be published, recent experimentation with the other coating materials and deposition systems was consistent with the observations reported here.
