Study On Arc-Sprayed Cored Wires And Wear Properties Of Coatings

Several coating systems against abrasive wear and erosive wear at elevated temperatures have been designed in this dissertation. Cored wires for arc spraying were fabricated by using low-carbon steel and nickel sheaths to hold the alloy-powders, and Cr3C2 ceramic powders. Adhesive strength, hardness and the thermal shock resistance of spraying coating were tested. Coating microstructures were assessed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectrometry (EDS). The effect of rare earth elements on abrasive wear of FeNiBCrSi coating was investigated. Characteristics and mechanism of erosive wear at elevated temperatures in MC coating and nickel-based spraying coating were studied, and the hot corrosion behaviors of the spraying coating at 650癈 was characterized. The results obtained from these studies provided a theoretical basis for their industrial application. The main results are summarized as follows:FeNiBCrSi coating was designed by using self-fluxing alloy with the addition of rare earth element of certain amount. The coating exhibited a high adhesive strength of more than 57MPa. The results indicated that the rare earth elements increased the hardness of the coating. The optimal range of hardness improvement through rare earth element addition was found to be 0.5~1.0%. The rare earth elements render better wear resistance to the coating. However, the wear resistance of the coating did not show a linear increase with the content of rare earth elements. When the content of rare earth elements is larger than 0. 7%, the wear resistance tends to be stable after slight drop. The mechanism of increasing wear resistance by rare earth element addition is that these elements increase the plasticity and harness of the coating, increase the adhesive strength between the hard phase and the base material,effectively protect boron which forms the hard phase, and rapidly increase the transition factor of boron, so that they can provide the coatings with better properties against wear. The wear mechanism of the coatings with rare earth element addition during abrasive wear is that fracture was resulted from repeated plastic deformation. The hardness of the coating was found to increase after wearing. When the content of rare earth elements is above 0. 7%, the hardness of the coatings increases rapidly. B15 coating, in which the content of rare earth elements is 1. 5%, was found to be the optical recipe with the comprehensive analysis of the abrasive wear property, elevated temperature oxidation, and thermal shock resistanceArc sprayed protective coating was developed from MC (Fe/Cr3C2) cermet to prevent erosive wear and hot corrosion at elevated temperatures. With systematic investigation of high temperature erosion property of MC arc sprayed coatings, and the effect of coating' s structure made from cermet on the property of erosive wear, the MC2 protective coating was achieved with a relatively high (>60MPa) adhesive strength, microhardness, as well as excellent properties against thermal shock and erosive wear at elevated temperatures. Plastic erosive wear contributed the most to the wear behaviors of MC coatings at elevated temperatures.Two types of new thermal spraying cored wires were fabricated with prefab Cr-B-Si powder, Cr, Cr3C2, and small amount of B-Fe powder covered by pure nickel sheaths. The adhesive strength, microstructure, phase formation, microhardness, thermal shock property, and erosive wear at elevated temperatures of nickel-based arc spraying cored wires were investigated. Same properties of the PS45 high Ni-Cr commercial solid wire spraying coating were also investigated. The coatings generally exhibited relatively high adhesive strength, microhardness, and excellent thermal shock resistance. The NiCrBSi and Ni/Cr3C2 coatings showed good erosive wear resistance at 650C . The Ni/Cr3C2 coating showed good erosive wear resistance at 750C. The erosion rate of the nickel-based coating reachedthe peak at an impact angle of 60 degrees. Certain brittl...