Effects of rare earth oxide on the nucleation of carbide particles in laser cladded MMCp coating

Abstract

Particulate reinforced metal matrix composite (MMCp) has excellent properties such as good wear resistance, corrosion resistance and high temperature properties. Various volume fractions of ceramic particles are usually deposited onto the metal surface to form MMC with improved performances by laser cladding. Recent literatures show that laser melting powders containing carbide-formation elements and carbon, is favorable for the formation of in situ synthesized carbide particles in MMC.Researches approve that the rare earth oxide (RExOy) plays a very important role in the precipitating of the in situ synthesized carbide particles especially as a heterogeneous nucleus of the carbides, which will greatly increase the distributing density of the enhanced particles. RExOy is commonly used to increase the laser absorptivity of the coating powder, to decrease the activity and improve the solubility of the alloy elements in the laser melt. At present, many researches have been made on the refinement of crystal grain by adding RExOy. However, nearly few have been reported on the accelerating of nucleation of the reinforcement particles as heterogeneous nuclei, especially in the field of laser producing MMCp.By the observation and analysis of SEM, EDS and TEM, it is found that in the precipitating of the carbide particles, some of the RExOy are partially dissolved, while the other ones change into rare earth carbides. However, both of them act as heterogeneous nuclei for the forming of particles. A clear interface between the nucleus and periphery of the particle can be observed by SEM after etching due to their differences in composition and structure. After deeply etched, the nuclei may be completely eroded and then left holes.Particulate reinforced metal matrix composite (MMCp) has excellent properties such as good wear resistance, corrosion resistance and high temperature properties. Various volume fractions of ceramic particles are usually deposited onto the metal surface to form MMC with improved performances by laser cladding. Recent literatures show that laser melting powders containing carbide-formation elements and carbon, is favorable for the formation of in situ synthesized carbide particles in MMC.Researches approve that the rare earth oxide (RExOy) plays a very important role in the precipitating of the in situ synthesized carbide particles especially as a heterogeneous nucleus of the carbides, which will greatly increase the distributing density of the enhanced particles. RExOy is commonly used to increase the laser absorptivity of the coating powder, to decrease the activity and improve the solubility of the alloy elements in the laser melt. At present, many researches have been made on the refinement of crystal g...