Research On Microstructures And Properties Of FeMnCrNiAlBSi/Cr₃C₂ Coatings

In this study, a new cored wire material which using mild steel band as sheath material, Mn, Cr, Cr₃C₂, NiAl/NiAl2 intermetallic compound, FeB, FeSi and FeSiRE as cores was prepared. Four kinds of good erosion resistance FeMnCrNiAlBSi/Cr₃C₂ coatings (respectively C1, C2, C3, C4) which were suitable for boiler tubes of coal-fired power plants were prepared on the 20 steel substrates by supersonic arc spraying. The microstructure, microhardness, bond strength, cohesive force, thermal shock resistance, high temperature oxidation resistance and high temperature erosion resistance of four kinds of coatings had been researched by means of a series of tests, and it had been analyzed by using modern testing techniques, such as Metalloscope, Scanning Electron Microscopy(SEM), Energy Dispersive Spectrometer(EDS), X-ray Diffractometer(XRD), et al.The results show that: The four kinds of coatings show typical layered structure characteristics, and they are high density. The organization and structure of the coatings consists of solid solution phases, oxide phases and pores. The solid solution phases contain Fe, Mn, Cr, Ni and Al elements. The solid solution phases of C3 and C4 contain B, Si elements in addition. The oxide phases contain Fe, Mn, Cr, Ni, Al and O elements. All the coatings show relatively high microhardness, among which the average microhardness of C3 coating is 454.5 HV0.1. All the coatings have relatively high bond strength, among which the bond strength of C4 coating is 11.5MPa. The cohesive strength of all the coatings is higher than 180MPa, among which the cohesive strength of C3 and C4 is respectively 246.6MPa, 258.7MPa, and it can meet actual requirements well. The morphology of tensile fracture presents as the combing characteristics of brittle and ductile, dimples morphology is obvious in C4 coating. Obvious cracks have been found in the four kinds of coatings through more than 23 times of thermal shock resistance test, coatings shed from the substrates through more than 27 times of thermal shock resistance test. C4 coating shows the best thermal shock resistance.The result of 100 hours oxidation test shows that the high temperature oxidation resistance of C1, C2, C3, C4 coating is respectively 6, 5, 9, 7 times higher than that of 20 steel, which is used for boiler tubes. Fe2O3, Iron chromium oxide and manganese aluminum oxide are formed on all the coatings. The integrated and dense oxide film is formed on the surface of C3 coating. The content of Al element of C3 film is the highest, which is 20.50At%. The content of Cr element of layer oxide of C3 coating is relatively high, which reaches 18.20At%. The cross-section oxidation degree of the four kinds of coatings from worse to best is respectively C1, C2, C4 and C3.The erosion rates of the four kinds of FeMnCrNiAlBSi/Cr₃C₂ coatings are all highest at the angle of 60°. The characteristics of high temperature erosion wear resistance of coatings are between ductile material and brittle material, the erosion rates are all obvious lower than that of 20 steel, among which C3 coating shows the best high temperature erosion wear resistance. The damage of FeMnCrNiAlBSi/Cr₃C₂ coatings which made by abrasive is obviously slighter than 20 steel, the morphologies of the coatings present as the characteristics of ductile material.Compared with the other three coatings, C3 coating has uniform and compact organization structure, relatively high bond strength, cohesive strength , good thermal shock resistance, highest microhardness, best high temperature oxidation resistance and high temperature erosion wear resistance, so it can be used as the anti-erosion protective coating on the boiler tubes of power plants.