Laser cladding in-situ carbide particle reinforced Fe-based composite coatings with rare earth oxide addition

Particulate reinforced metal matrix composite (PR-MMC) has excellent properties such as good wear resistance, corrosion resistance and high temperature properties. Laser cladding is usually used to form PR-MMC on metal surface with various volume fractions of ceramic particles. Recent literatures showed that laser melting of powder mixture containing carbon and carbide-forming elements, was favorable for the formation of in-situ synthesized carbide particles. In this paper, rare earth oxide (RE2O3) was added into the clad powder mixture to investigate the effects of RE2O3 on the in-situ carbide particle formation in Fe-based composite coatings. Through the analysis using scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS) and transmission electron microscope (TEM), it was revealed that: (1) Adding RE2O3 to the Fe-based powder mixture could effectively reduce cracks and porosities and the coating surface was more smooth; (2) The solubility of carbon could be improved which increased the eutectic degree of the microstructure; (3) RE2O3 could promote the nucleation of the reinforcement particles as heterogeneous nuclei. During the precipitating process of the carbide particles, some RE2O3 powders still existed while others react with carbon in the melt to form rare earth carbides. Both of them acted as heterogeneous nuclei for the formation of particles.