Research On Composite Coatings Of Cemented Carbide And Their Cryogenic Treatments

Three kinds of composite coatings, TiCrN, TiAlCN and CrAlTiN coating were deposited on YG6 cemented carbide by multi-arc ion plating technology. The microstructure and properties of the composite coatings were characterized, and the effects of cryogenic treatment on composite coated cemented carbide were studied. The results show that:(1) For TiCrN composite coating, the surface of the coating is smooth. And there are a few droplets of different sizes, large particles as well as many small pits on the film. The main phases of TiCrN composite coating are WC phase and(Ti, Cr)N phase, and the(111) crystal plane of(Ti, Cr)N phase shows a preferred orientation. The hardness of the coating is 2112 HV. The adhesion of the coating is 55 N. For electrochemical corrosion, the broken blunt potential Eb of TiCrN composite coating is 0.8847 V, the passive region ?E of TiCrN composite coating is 1.6527 V, and there is little corrosion pits on the coating surface, and there are the cracks as well as radial cracks appearing in the corrosion pits. After cryogenic treatment, the tendency of preferred orientation has changed with the cryogenic treatment time. And the coating cryogenically treated for 30 hours shows the highest hardness and adhesion strength.(2) For TiAlCN composite coating, there are small dimensions particles with different size and tiny holes on the surface of the coating. And the main phases of TiAlCN composite coating are WC phase and(Ti, Al)(C, N) phase. The hardness of the coating is 2311 HV. The adhesion strength of the coating is 47.5 N. For electrochemical corrosion, the broken blunt potential Eb of TiAlCN composite coating is 1.142 V, the passive region ?E of Ti AlCN composite coating is 1.699 V. In addition, there is only a small amount of corrosion pit on the coating surface, and there are no cracks and radial cracks in the corrosion pit. After cryogenic treatment, the intensity of(Ti, Al)(C, N)(111) crystal plane diffraction peak decreases with the extension of cryogenic treatment time gradually. The hardness of coatings that cryogenically treated for 20 hours is the lowest. Subsequently the hardness of the coating increases with the cryogenic treatment time. And the hardness of the coating that cryogenically treated for 40 hours is the highest. The adhesion strength of the coating that cryogenically treated for 30 hours is the highest up to 52 N.(3) For CrAlTiN composite coating, there are irregular particles of smaller size and some smaller size holes and a few pits on the surface of CrAlTiN composite coating. And the main phases of CrAlTiN composite coating are WC phase and(Cr, Al, Ti)N phase. The hardness of the coating is 2321 HV. The adhesion strength of the coating is 70 N. For electrochemical corrosion, the broken blunt potential Eb of CrAlTiN composite coating is 0.8603 V, the passive region ? E of CrAlTiN composite coating is 1.3999 V, and there are cracks on the coating surface. In addition, the width of cracks become larger and deeper, and the inner of cracks exist smaller cracks and corrosion pits. There are different degrees of corrosion on the coating surface, indicating poor corrosion resistance of CrAlTiN composite coating. After different time of cryogenic treatment, the coating diffraction peaks have a certain extent shift to the left. This is because of Al, Ti atoms dissolving in CrN lattice, replacing the Cr atoms, thus the lattice constant increases. The coating hardness decreases with the cryogenic treatment time, and the coating cryogenically treated for 40 hours is of the largest decline, which indicating that prolonging the cryogenic treatment time is bad for coating hardness. The adhesion strength decreases with the cryogenic treatment time.(4) The three composite coatings were compared under the existing conditions, the hardness and adhesion strength of CrAlTiN composite coating is the highest, while broken blunt potential Eb, passive areas ?E are minimized, thus the corrosion resistance of CrAlTiN composite coating is the worst. The hardness of TiCrN composite coating is the minimum; TiAlCN composite coating is of the lowest adhesion strength and the broken blunt potential Eb, passive areas ?E are the largest thus the corrosion resistance is the best. The hardness of TiCrN composite coating cryogenically treated for 30 hours is the largest up to 2273 HV. And the hardness of TiAlCN composite coating cryogenically treated for 40 hours is the largest up to 2401 HV. The hardness of CrAlTiN composite coating decreased with cryogenic treatment time, and the coating without treatment is of the largest hardness. The adhesion of TiCrN, TiAlCN composite coating shows a similar law as the cryogenic treatment time, the adhesion strength are the highest with cryogenically treated 30 h. While the adhesion strength of Cr AlTiN composite coating decreases with cryogenic treatment time.