Preparation and characterization of in situ synthesized B4C particulate reinforced nickel composite coatings by laser cladding

The preparation and characteristic of in situ synthesized B4C particulate reinforced nickel composite coatings on A3 steel substrate by laser cladding, especially the microstructure and wear-resistance of this coating have been investigated. Good finish and in situ synthesized B4C particulate reinforced composite coatings can be achieved employing a proper amount of (B2O3 + C)-doping under a suitable laser power and scanning velocity. It is found that a new white particulate phase appears in the coatings. The microstructural and metallographic analyses made by a scanning electron microscopy, energy-dispersive spectrometer and X-ray diffractometer suggest that the new white particulate phase includes the in situ synthesized B4C in laser cladding process. The white particulate, together with the acicular dendrite, presents as the primary reinforcements of the coatings. Because of the generation of these particulates and their homogeneous distribution in the matrix, the composite coating gives very high hardness of Hv0.31400 and excellent wear resistance, which is two times higher than that of pure Ni60 coatings. In addition, the bottom, center and upper region in the composite coatings exhibit the different microstructure. The microstructure in the bottom region consists mainly of acicular dendrites dispersed in the γ(NiFe) matrix. And that the microstructure located at the center and upper regions contains both acicular dendrites and white particulates dispersed in the matrix of the interdendritic lamellar eutectic. Moreover, the number of white particulates in the upper region is more than that in the center region.