Improvement of interfacial bonding between plasma-sprayed cast iron splat and aluminum substrate through preheating substrate

During the plasma spraying process, the splat-substrate interaction is a key factor to understanding the formation of the coating-substrate adhesion. In the present study, both experimental and simulation methods were employed to analyse the splat-substrate interfacial bond and its formation. Individual cast iron splats were sprayed onto polished aluminum substrate surfaces, which were preheated to temperatures ranging from 25 °C to 240 °C. After spraying, polished cross sections of the collected splats were examined by scanning electron microscopy to identify the splat-substrate interface bonding characteristics. Furthermore, numerical simulation was conducted using a finite element method (FEM) to obtain quantitative information on heat exchange between the splat and the substrate. Results showed that the substrate preheating temperature (initial substrate temperature) significantly affected the splat-substrate bond formation. When the initial substrate temperature exceeded 190 °C, the formation of a metallurgical bond at the splat-substrate interface was detected. The results of the analysis based on both experimental and simulation data, demonstrated that the higher initial substrate temperature caused obvious plastic deformation of the substrate surface and atomic diffusion at the splat-substrate interface under the present conditions, which contributed to the formation of the metallurgical bond. Moreover, a barb-shaped structure was found at the periphery of the splat when the initial substrate temperature reached 240 °C, which was beneficial to the enhancement of the mechanical bonding between the splat and the substrate.