| Erosion wear by solid particles is a serious problem in many engineering fields. Coatings, as the barrier of the parts surfaces, can protect the parts from being eroded by solid particles. Coatings with small thickness are produced suitably using PVD technology, which has very small effects on the mechanical performances of the substrate. Therefore, it has been a hot subject that PVD coatings are used to improve the erosion resistance of parts. TiN, TiAIN, CrN, CrAIN, CrAlTiN coatings were produced by PVD technologies in this investigation. The erosion characteristics and wear mechanisms of the coatings were investigated in this paper.Two hard metals, WC/TiC/Co and WC/Co, and a stainless steel, 1Cr18Ni9Ti were used as substrate materials. Four coatings, TiN, CrN, CrAIN and TiAIN were produced by pulsed filtered vacuum cathode arc deposition assisted with ion bombardment. CrAlTiN coating was deposited using unbalanced magnetron sputtering. Phases, morphologies, elements distributions, compositions of micro fields, crystallographic sequences and interfaces were analysed. It was shown that the main phases were the corresponding nitrides. It was discovered that the coatings were dense and the elements were well distributed. Good bonding exsisted between the coating and the substrate. There was some element diffusion between the substrate and the coating. There were both physics and elementen diffusion bonding between the substrate and the coating. Phasical and mechanical performances of the coatings were measured. The hardest coating was TiAIN coating with hardness of 32.40 GPa and the softed coating was CrN coating 16.50 GPa. The coating with the highest and the lowest elatic modulus was that of TiAIN coating and CrN coating, and their modulus was 580 GPa and 360 GPa respectively. The coating with highest adhension strength is CrAIN coating on WC/Co and the coating with the lowest adhension was CrAlTiN coating, and their adhension strength was 88.56 N and 48.36 N, respectively. The residual stress was compressive for the coatings on the hard metals and tensile for most of the coatings on the stainless steel.It was shown that the erosion wear characteristics of the coatings on different substrates by analyzing the results of the erosion tests. The ranking of the erosion rate of of the substrate WC/TiC/Co and the coatings on it was TiAlN<CrAlN<WC/TiC/Co <TiN< CrN. The erosion rate of the TiAIN coating was only 1/4 times of that of the substrate WC/TiC/Co. The ranking of the erosion rate of the substrate WC/Co and the coatings on it was CrAlN<TiAlN<CrAlTiN<TiN<WC/Co, and the erosion rate of the CrAIN coating was 1/3 times of that of the substrate WC/Co. The ranking of the erosion rate of the substrate 1Cr18Ni9Ti and the coatings on it was CrAIN<TiAIN<CrAlTiN <TiN<1Cr18Ni9Ti, and the erosion rate of the substrate 1Cr18Ni9Ti was 3.9 times of that of the CrAIN coating on it.It was revealed that the effects of the mechanical performances of the coating on its erosion resistance by analyzing their relation.. It was that the union of the hardness and the elstic modulus affected the erosion resistance of the coating instead of the affecting from the hardness or the elastic modulus alone. It was shown that the effects of the substrate performances on the erosion resistance of the coating by analyzing the relation between the characteristics of the substrate material and the erosion rate of the coating. It was discovered that the erosion resistance of the coating was not dependent on the substrate completely. The erosion rate of the coating was much lower as the elastic modulus of the substrate was comparable to that of the coating.The erosion surface morphologies of the coatings were observed. It was found that the erosion damage began from the microstructure defects of the coatings. The coatings deposited by pulsed filtered vacuum cathode arc deposition assisted with ion bombardment were eroded from the growth defects of the microstructure in the coatings surfaces. The coatings deposited by unbalanced magnetron sputtering were eroded from the pits in the surfaces of the coatings.The erosion model was built for angular solid particles based on the theory of indentation fractur mechanics. The volume of the coating material removed by a single angular solid particle was analysed. A function with two mechanical parameters, the hardness and the elstic modulus of the coating, was used to describle the volume of the coating removed by a single solid particle. The effect of mechanical performances on the coating volume removed during the erosion was revealed with this function. The validity of the function was discussed with the erosion morphology of the coating surface.By analyzing the macro and micro morphologies of the erosion surfaces of the coatings and the micro morphologies of the cross-section of the erosion scar, the erosion wear mechanism of the coating was discussed. The main erosion mechanism of the TiN coatings was brittle fatigue fracture of the coating material. The erosion mechanisms of the TiAIN coatings varied with the substrates. The main erosion mechanisms of the TiAIN coating on WC/TiC/Co substrate were micro cutting and brittle fatigue fracture, while the TiAIN coatings on WC/Co substrate was brittle fatigue fracture. The main erosion mechanisms of TiAIN coating on 1Cr18N1i9Ti substrate were micro cutting, ductile fatigue fracture and brittle fatigue fracture. The main erosion mechanism of CrN coating on WC/TiC/Co substrate was brittle fatigue fracture. The main erosion mechanism of coating CrAlN on WC/TiC/Co was brittle fatigue fracture, while the main damage mechanism of coating CrAlN on WC/Co was ductile fatigue fracture. The main erosion mechanism of coating CrAlN on 1Cr18N1i9Ti was micro cutting and brittle fatigue fracture. The erosion mechanism of CrAlTiN coating was micro cutting and brittle fatigue fracture. The coating material at the edge of the pit, which were the growth defect of the coating structure, was removed in the way of micro cutting and brittle fatigue fracture.
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