Research On Laser Cladding Ni/SiC Composite Coatings And The Capability Of Them

In this article, we have carried out laser cladding experiments of Ni60 powders and Ni60 with different weight percentage of SiC composite powders on the surface of 45 steel substrate through a GFT-IVB 7kw crosscurrent type of CO2 laser apparatus. A proper material system and laser cladding parameters were ascertained by the comparison of analyses basing on the microscopic and macroscopic qualities of different cladding layers. By the means of OM, SEM, XRD etc., different layers' phase constitution and microstructure were observed and analyzed, the mechanism of SiC enforcement was also expatiated. Through a kind of disc-pin tribological wear experiment machine, we carried out tribological wear experiments on the surface of 45 steel, Ni60 coatings and Ni60 with different weight percentage of SiC composite coatings, the tribological wear mechanism was also discussed basing on the tribological wear configuration of variant wear experiment samples. Through a self-made erosion experiment machine, we carried out erosion experiments of laser cladding samples, and the erosion mechanism were discussed too. In the end, we made some useful discussion of different cladding layers' corrosion behavior by the way of polarization curves.Laser cladding parameters have great impact on the microstructure, macro-configuration and the capability of the cladding layers. Under the cladding parameters of P=3kw, Vs=3mm/s, D=5mm, we obtained cladding coatings with good surface quality, fine microstructure, low dilution, high micro-hardness and good metallurgical combination interface with 45steel substrate.The microstructure analysis results showed that, from the surface of the cladding specimen to the substrate 45steel, there are three distinct areas: the cladding area, the bonding area and the heat-affected area in the substrate. With the different solidification character parameters, it takes on different microstructure in the cladding layers. The typical microstructure was the typical extension growth on the plane basis at the bottom of the layers, cellular crystals near the bonding area, .dendrite crystal in the middle of the cladding layers and fine equi-axed crystals on the top of the layers.Laser cladding layers mainly consists of Y -Ni, Ni2.9Cr0.7Fe0.36, Fe7C3, Fe0.79C0.12Si0.09, but single SiC phase is not found. Under the optimized cladding parameters, the temperature in the molten pool is far higher than the SiC decomposing temperature, which results one part of SiC was bumed while the others were decomposed of C and Si. The new hard phase which composing of C, Si and self-confusion alloy element enhanced the cladding layers along with the vehemence solid solutionintensification and the remaining stress.Tribological wear experiments result shows the wear capability of Ni60 is 4 to 6 times as high as that of the 45steel substrate. Once the Ni60 self-confusion alloy affiliated with SiC, the tribological wear capability enhanced. Under the same cladding parameters, the tribological wear capability of Ni60+25%SiC composite coatings are 30 to 50 percent higher than that of the Ni60 self-confusion alloy. In addition, the erosion capability of Ni60 coatings is far better than that of the 45steel substrate, not to mention that of the Ni60+25%SiC composite coatings.Polarization cure shows both the Ni60 and Ni60/SiC composite coatings' corrosion current density is far less than that of the 45steel substrate, which manifests the corrosion velocity of 45steel far lower than that of the Ni60 and the Ni60/SiC coatings. However, we found that the corrosion resistance of Ni60/SiC composite coatings is worse than that of pure Ni60 self-confusion alloy.