Study On The Enhancement Of La₂O₃ On The Laser Clad WC/Ni-based Ceramic-metal Composite Coating

Laser cladding is an advanced material surface modification technology by using high power laser ray to melt the substrate and the specific metal powder added on its surface to make a close metallurgical bonding. Based on laser cladding technology, researchers make one step further by developing metal-ceramic laser cladding technology, laser ray is used as power source to heat the metal-ceramic powder in order to make a metallurgical bonding. Compared with the substrate, metal-ceramic coating has high microhardness, good wear resistance and corrosion resistance and etc. WC/Ni metal-ceramic powder is used as the most common metal-ceramic cladding powder.The effects of laser processing parameters on the formability(clad width, clad height, clad depth) of coatings are studied by laser cladding La2O3/WC/Ni60 ceramic-metal coatings with different laser processing parameters on the surface of Q235 substrate. It is concluded that the best La2O3/WC/Ni metal-ceramic laser cladding parameter for the formability is: Power 2000 W, Scanning speed: 100mm/min, Spot diameter 2mm, Pre-heat temperature T=300℃, Shield gas flow rate 10L/min. According to the processing parameters above, 60wt%Ni60+40wt%WC coatings with different mass fraction of 0,0.6%W,1.0%,1.4%W La2O3 respectively were cladded on the surface of Q235 substrate. SEM, EDS, XRD were used to analyze phases, microstructure and morphology. Friction wear testing machine, salt spray corrosion test chamber, mircrohardness tester were used to test the microhardness, wear resistance, corrosion resistance of the coatings. Combining all the results above, the effects of rare earth La2O3 on the microstructure, morphology, Phase composition, metallurgical behavior, physical and chemical properties are studied. It is concluded that: with appropriate amount of rare earth(1%W) addition, the microstructure of the coatings are purified and refined, improve the well-distribution of the coating, reduce the amount of brittle inclusion, decrease the tendency of pores, inclusion, segregation and cracks, creating good metallurgical bonding between the substrate and coatings; XRD indicates that the most phases in the coatings are γ(Fe,Ni)、WC、M23C6 and Ni3 B,after the addition of La2O3,La reacted with the other elements in the coatings produced new phases such as La3BO6,La2Ni7,the addition of La2O3 can increase nucleation rate of the molten bath, and accelerate burning loss of WC particles, improve the distribution and wetability between WC and the metal substrate, increase the amount of hard phases in the coatings. microhardness, wear resistance and salt spray corrosion tests indicate that with the amount increase of La2O3,the microhardness, wear resistance and corrosion resistance increase and the decrease, with the 1.0%W addition of La2O3,the micro hardness of the coatings reaches highest level(HV700),the wear resistance and corrosion resistance are best which are much better than the coating without La2O3.