Microstructural characterisation of laser clad coating of nickel based alloy with dissolved SiCp

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Abstract
A laser surface cladding technique was used to form an Ni–Cr–B–Si–C alloy coating doped with 30 vol.-%SiCp on an AISI 1045 steel substrate. The SiC particles completely dissolved during the melting stage of cladding. The bonding zone has a microstructure of a γ-Fe band resulting from epitaxial planar growth followed by a cellular dendritic eutectic of γ-Ni + M23 (C,B)6 on solidification, characterised by directional solidification. The microstructure of the cladding layer is composed of very closely spaced net-like M23 (C,B)6 primary dendrites and a small amount of interdendritic γ-Ni + M3 (B,Si) lamellar eutectic, and has primary small spherical graphite particles in the upper part of the cladding layer. The rapid solidification involved in the laser cladding resulted in substantial extension of solid solubility of Si in the γ-Ni terminal solid solution. The M23 (C,B)6 primary dendrites contain a high density of stacking faults. The eutectic M3 (B,Si) phase exhibits a periodic structure.