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Preparation of a Double Layer Composite Coating on a Steel Substrate by Laser Cladding
Q.L. Wu, W.G. Li, N. Zhong, C.H. Fan, B.Y. Liu and Y.S. Ying

A double layer composite coating on Q235 steel substrate was prepared using a new developed in situ technology consisting of a self-propagation high-temperature synthesis (SHS) reaction, laser cladding and metal dusting techniques. The samples were subjected to various microstructural examinations and the microhardness was also measured. A double layer composite coating consisted of TiO2–TiC ceramic outer layer and a TiC-carbon nano-tubes (CNTs) cermet inner layer. An excellent bonding was observed among the outer layer, the inner layer and the steel substrate. The TiO2 distributed uniformly in the microstructure and a small number of porosities were seen in the outer layer. The cermet inner layer consisted of γ-(Fe, Ni) as a metallic matrix binder and TiC-CNTs as a reinforced phase in the microstructure. The hardness of the coating was significantly higher than that of the substrate.

Keywords: CO2 laser, TiC, TiO2, carbon nano-tubes (CNTs), laser cladding, self-propagation high-temperature synthesis (SHS), metal dusting, microstructure, microhardness

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