Particle distribution and microstructure of IN718/WC composite coating fabricated by electromagnetic compound field-assisted laser cladding

Abstract

In this study, IN718/WC composite coatings were fabricated by electromagnetic compound field-assisted laser cladding. The macrostructure, microstructure, and microhardness of the coating were systematically investigated. The results show that the electromagnetic compound field induces the downward Ampere force, enhancing the Marangoni convection in the molten pool. The enhanced Marangoni convection makes the WC particles uniformly distributed in the composite coating. However, excessive Marangoni convection causes the WC particles to escape from the molten pool, especially the small WC particles. The application of 20 mT steady magnetic field in combination with 100 A direct current field is appropriate. It is found that the WC particles are decomposed in the molten pool, resulting in the formation of sub-micron eutectic carbides, feather-like eutectic carbides, and equiaxial eutectic carbides. The WC particle decomposition is related to the spatial position of WC particles and the distance between WC particles. The higher the spatial position of the WC particles (relative to the molten pool) and the greater the inter-WC particle distance, the more severe the decomposition. In addition, the direct current increases the nucleation rate of eutectic carbides, and the enhanced Marangoni convection breaks the long columnar eutectic carbides, which collectively refine the microstructure of the coating. The diffraction intensities of the reinforcing phases in the above case (20 mT, 100 A) are the highest, and the microhardness (530 HV0.2) exceeds that of the coating (400 HV0.2) fabricated by unassisted laser cladding.