A Novel Strategy for Depositing Dense Self-fluxing Alloy Coatings with Sufficiently Bonded Splats by One-Step Atmospheric Plasma Spraying

Self-fluxing alloy coatings are usually utilized by spray fusing two-step process for fully dense microstructure and metallurgical bonding to the substrate. The fusing process brings out limitations for coating applications due to the need of high-temperature fusing. In this study, it is found for the first time that metallurgical bonding between NiCrBSi splats can be achieved by deposition of super-hot droplets created by plasma spraying. Thus, a sufficiently dense NiCrBSi coating can be prepared by one-step plasma spraying. NiCrBSi powders with a size range of 30-50 mu m were used as typical material for plasma spraying. The particle temperatures were measured by a DPV-2000 thermal spray in-flight particle diagnostic system. The microstructure of coatings was characterized using scanning electron microscopy. Results show that particles can be heated to a significantly high temperature over 2400 degrees C by the optimal design of the nozzle internal structure, and the plasma-sprayed NiCrBSi coatings are almost fully dense with effective metallurgical interparticle bonding. Based on the numerical simulation result of the interfacial temperature evolution between spreading splat and NiCrBSi substrate, a self-fusing mechanism is proposed for plasma spraying of NiCrBSi. Furthermore, the coating prepared by one-step plasma spraying reveals superior abrasive wear resistance and corrosion resistance as compared with the flame spray and fusing counterpart. It is clearly demonstrated that the new approach to deposit highly dense coatings directly by plasma spraying with self-fusing effect could greatly expand the applications of fluxing alloy coating materials.