Study On The Ceramic-metal Composite Coatings On The Surface Of Carbon Steel By Laser Cladding

Laser cladding is a new kind of surface modification technique, which uses high energy laser beam to melt the cladding materials and to coagulate them on the surface of the base materials. Laser cladding coating has high strength, good process property, high wear resistance, corrosion resistance, heat resistance and so on. Showing many engineering applications, laser cladding is becoming one of the best important research domain in many subjects such as material science, metallurgical engineering and mechanical engineering[1,3].In this research, a ceramic-metal composite material for laser cladding was prepared. A precursor was synthesized from ZrOCl₂·8H₂O, Cr₂O₃ , Ni(NO₃)₂·6H₂O and NH₄HCO₃ as raw materials by using a improved coprecipitation method. The precursor was calcined into the compound oxide of nickel, chrome and zirconium, which reduced at high temperature to form NiCr-ZrO₂ composite powder material. The thermal properties, structures and particle distribution of the composite powder were characterized by TG-DSC, X-ray diffraction and laser particle analyzer. The relationship between the thermal expansion coefficient and the composition of NiCr-ZrO₂ composite material was studied. The result showed that the thermal expansion coefficient of NiCr-ZrO₂ composite material increased gradually with the increasing of metal content in the ceramic-metal composite material. The NiCr-ZrO₂ powder materials were melted on a surface of carbon steel by laser cladding. The microstructures of the coating surface and cross section were detected by SEM. The elements of the laser cladding coating were measured by XPS. The results showed that the density of the coating increased and the dilution ratio decreased with the metal content in the laser cladding coating increasing.The corrosion resistance of the coating was studied by a weightlessness experiment and electrochemical tests including AC impedance and polarization techniques. The result showed that the mass loss rate of the coating decreased with the increasing of metal content. Moreover, as the metal content in the coating increased, the impedance increased and corrosion current density decreased, which showed the improvement of the coating corrosion resistance.