Effects of CeO2 on Forming Quality and Microstructure of TiCx-reinforced Ti-based Laser Cladding Coating

Ti6Al4V+ NiCr-Cr3C2 multi-track overlapping cladding coating without and with 2% CeO2 was successfully prepared on the surface of Ti6Al4V via using coaxial powder feeding laser cladding technology. The effects of CeO2 addition on the forming quality, microstructure and element distribution of cladding coating was investigated by penetrant flaw detection technology, OM, XRD, SEM, EDS, EPMA and other analytical methods. The results show that the addition of CeO2 completely inhibits the surface cracks on the cladding coating and significantly decreases the porosity from 2. 76% to 1. 65%. The microstructure of cladding coatings are mainly composed of beta solid solution (CrTi4) and vacant titanium carbide (TiCx). The addition of CeO2 has no effects on the phase types of the cladding coating except for the recrystallized CeO2. Futhermore, the addition of CeO2 leads to a distinct segregation of Ni and Cr element in the matrix, especially for Ni, while elements Al and V are relatively evenly distributed. The recrystallized CeO2 is mainly distributed at the phase boundary between the TiCx and CrTi4. Adding CeO2 refines the TiCx dendrite and reduces the relative content of dendritic TiCx from 55% to 40%. The microstructures of titanium carbide in the different zones (such as cladding zone, transitional zone and bonding zone) of the cladding coating are exhibited significant difference, and their microstructural features are dendritic, particulate, and fine needle-like, respectively. The content of element C in the vacant titanium carbide TiCx also shows a significant difference, the value of x ranges from 0. 21 to 0. 74, and the C in primary dendrite is higher than that of secondary dendrite. The results of hardness and friction wear test show that the microhardness of Ti6Al4V substrate, the composite coatings without and with 2% CeO2 is 363. 2, 488. 2 and 464. 2 HV0. 5, respectively. And the wear rates are 5. 62x10(-6), 2. 5x10(-7) and 2. 43x10(-6) g/ Nmin, respectively.