RESEARCHON THE CRACKS OF Ni-BASED METAL-CERAMICCOMPOSITE COATING BY LASER CLADDING

In-situ synthesized TiB₂ / Ni metal-ceramic composite coatings with different compositions were fabricated on the medium carbon steel using laser cladding. The cracking behavior in different coatings was studied bymicroanalysis. The result s show that the cracks formed in the coating with high content of ceramic phases are mainlythe following : the t ranscrystalline cracks in the bonding metal mat rix, the high density cracks at the edge of thecoating, micro-cracks on the interface of the mat rix and the hard ceramic phases and in the vicinity of the bondinginterface in the heat-affected zone, etc. The cracks in the coating are mainly caused by the thermal st ress induced bythe difference of the thermal expansion coefficient s of the coating materials and the metal mat rix, and the t ransformation st ress plays an important role too. The good quality coating can be obtained by optimal laser parametersand coating compositions.