A Gauss Laser Pinning Method for Enhancing the Thermal Shock Resistance of Sprayed NiCoCrAlY Coatings

Abstract

A novel laser pinning reinforcement process was employed to enhance the thermal shock resistance of NiCoCrAlY coatings. The process parameters of the Gaussian laser pinning strengthening were tested and optimized to obtain the optimal process parameters. The influences of the central single-point, triangular, quadrilateral, hexagonal, and annular pinning on the microstructure and thermal shock performance of the coatings were studied. In the laser pinning zone, the uniformity and compatibility of the microstructure were significantly improved and the bonding mechanism between the coating and the substrate shifted from mechanical bonding to metallurgical bonding. The thermal shock cycling experiments demonstrated that after 9 cycles, the coating with the annular layout peeled off and failed. After 45 thermal shock cycles, the coating with the hexagonal layout peeled off and failed. However, after 296 thermal shock cycles, the coatings not pinned by the laser failed and the coatings with the central single-point, triangular, and quadrilateral pinning layouts had relatively intact surfaces, and the crack propagation was not obvious. Among them, the coating with the triangular pinning layout had the fewest cracks. Longitudinal cracks and edge cracks were generated within the limited area. As the thermal shock cycling continued, the edge cracks extended toward the center and connected with the longitudinal cracks, ultimately leading to the preferential peeling and failure of the coating. In contrast, the number of tiny cracks within the local range of the pinning points of the triangular layout was the least, and it was difficult for the cracks to connect, so the anti-thermal shock performance was the strongest.