Characterization and Control of Residual Stress in Plasma-Sprayed Silicon Coatings on SiC/SiC Composites

In order to reveal the relationship between residual stress in Si layers of SiC/SiC composites and the different parameters used in their preparation, the residual stress of the coating surface was tested using X-ray sin(2)psi technology and laser Raman spectroscopy. Then, the Raman shift-stress coefficient (P) and the Raman shift with free stress (omega(0)) were calculated as -201.41 MPa/cm(-1) and 520.591 cm(-1) via linear fitting with the least squares method. The results showed that all the as-sprayed Si coatings exhibited tensile stress on the surface, ranging from 53.5 to 65.9 MPa. The parameters of the spraying distance and second gas (H-2) flow rate were considered to be the most important for controlling the residual stress on the coating surface. Additionally, the surface tensile stress of the Si layers could be eliminated and even changed into compressive stress by annealing above 800 degrees C. Furthermore, the residual stress distribution in the cross-section of the Si layers was evaluated using laser Raman spectroscopy. Additionally, the particle characteristics, such as in-flight velocity and temperature, were investigated using a diagnostic system. The results of this research contribute to increasing the understanding and control of residual stress in APS Si bond layers.