Study On Laser Cladding Ni-based Metai-ceramic Coating

A (TiO₂+B₂O₃+Al₂O₃+TiB₂)/Ni-Cr-Al metal - cerami c co ating was fabri cated onChinese brand 40Cr steel by laser. TiB2, Al2O3 was introduced by an in situ reactionof Al, B2O3 and TiO2 during laser cladding process. The microsmicture, phase,elemen distribution and microhardness have been analyzed wth the aid ofmicroscope, X-ray diffraction, electron probe and microhardness-tester. It was shown that there are different solidification parameters for different zone in cladding layer, hence the different microstructure. The microstructures were typical extension growth on plane basis at the cladding layer bottom, Cellular crystals near the bonding zone, dendrite crystal in the middle of the molten layer and equiaxed crystals at the top of the cladding layer. Introduction of the ceramic made the microstructure very fine. Meanwhile, the grown direction of the dendrite is various because of the presence of the ceramic particle. It was observed that the disperse A1203 and T1B2 with the size of sub-micrometer formed in the grains and unreacted B203, Ti02 are distributed along the grain boundary. There is a ceramic density-gradient distribution along the depth of the cladding layer. The microhardness reveals a gradient variation versus to the depth and the highest value was 434HV0.2. Experimental results showed that the 7-Ni, j, Al203 and TiB2 are the dominant phases in the cladding zone, The microstructure and hardness of the cladding layer are governed by the laser processing parameters as well as the the coating chemical composition. The hardness and the wear property of the layer are significantly enhanced due to the present of ceramic in the coating.