Flattening Characteristics of Ni20Cr Thermal-Sprayed Coating Layers on Preheated SCM415 Substrates

Abstract

The preheating effect of SCM415 steel substrates on the flattening behavior of Ni20Cr flame-sprayed particles was investigated in a temperature range from 278 K to 523K. In the present study, we calculated the particle temperature and velocity distributions of the continuous and discrete phases before collision with the substrate by using a computational fluid dynamics (CFD) code of Fluent (ver. 6.3.26). Particle velocity and gas temperature decreased rapidly in the radial direction while the particles traveled toward the substrate, suggesting that substrate size and distance from the nozzle should be carefully controlled to improve coating quality. The conventional flame spray gun was used to accelerate molten particles and K-type thermocouples were used to monitor the substrate temperature during a preheating process. Commercially available nickel-based Ni20Cr particles with a mean diameter of 45 mu m and 20 mu m were used for experiments to examine the particle size effect on the coating characteristics. Herein we present FE-SEM images of coated layers on the substrates. As the substrate preheating temperature increased, the flatter surface morphology was seen at the interface between substrate and coating layer because of better wetting and corresponding higher shear adhesion strength. Moreover, the splat morphology was significantly dependent on the particle size. [doi:10.2320/matertrans.M2011068]