Microstructures And Cavitation-erosion-resistance Of Gradient TiC/Ni Coating By Plasma Cladding

By the use of plasma cladding technology, a gradient TiC/Ni composite cladding layer was synthesized on 45 steel. Microstructure and performance were analyzed by Transmition Electron Microscope (TEM), Scanning Electron Microscope (SEM), X-ray Diffraction (XRD), Optical Microscopy (OM) and Vickers hardness tester. Compared with ZG06Cr13Ni5Mo layer, two different TiC/Ni cladding layers containing particles with 3μm size and nano-step particles were studied in the cavitation erosion tests. Tracing observation to the changes in morphologies during the cavitation erosion process was achieved with the help of Zoom Stereo Microscope and Scanning Electron Microscope (SEM). Properties of cavitation resistance and cavitation erosion mechanisms of the layers were analyzed, while the range of residue of the specimens size was measured with Laser Particle Size Analyzer.Orthogonal experiment was designed to optimize the processing parameters with the help of range analysis. The gradation of parameters decided by their effect on the synthesized points of the coating is: working current, scanning velocity, laying method of TiC powder. The results show that when the mixture ratios of TiC powder in the pre-placed layers are prepared with a percentage order of 10%, 15%, 20% from the bottom to the top surface of the coating, working current is 140A, scanning velocity is 15cm/min, and granularity of TiC is 3μm, the composite cladding layer will show the best comprehensive quality. The maximal . microhardness value of the plasma cladding coating can reach HV 1088.γ-Ni, TiC, Ni₃B, M₂₃C₆ and boride of chrome phase were shown in the coatings. The microstructures of the coating matrix present distribution from dendrite crystal to cellular to planar. TiC particles exhibit a continuous decrease both in volume fraction and size from the top surface to bottom of the coating. The microhardness value of the plasma cladding coating is related to the distribution of TiC. The microhardness value appears a gradient decrease from the top to bottom of the coating except the surface.In the process of preparing cavitation examples, the plasma cladding equipment will make two lapped lines. Coarsened structures were observed at the overlapping part, while the microhardness decreased. In order to reduce the errors of cavitation experiments, 1Cr18Ni9Ti was used to take the place of the former matrix. The testing results indicate a same composition and not much difference in microhardness of the overlapping part. The cavitation erosion experiment is actualized according to the Chinese standard GB 6383-86, the curves of mass loss against time and cavitation erosion speed against time were obtained. The obtained curves show that the cavitation erosion resistances of the two cladding layer are all better than ZG06Cr13Ni5Mo, and the TiC/Ni cladding layers containing particles with 3μm size is the best one. The improvement in cavitation erosion resistance can be attributed to the solution strengthening ofγ-Ni matrix and the presence of large amounts of TiC with the size of 3μm which withstood the impingement of water micro-jet, While the agglomerated nano-step TiC disintegrate and desquamation before the matrix.