Abstract
Because of its high hardness ,wear resistance and good toughness ，tungsten carbide coatings have been widely used in mechanical, aerospace, automotive, water conservancy and printing industries etc. Which has a special project significance for improving the wear resistance of the parts and repairing the wear face of the friction.Extensive attention has been paid to plasma spraying as a kind of method for preparing tungsten carbide coating with low cost. However ,WC powders were easily oxidized in spraying process , then decarburization decomposition gave rise to the formation of W2C and CoxWyCz etc, even to metallic tungsten . Therefore the hardness, abrasion resistance and fracture toughness of the coating was reduced greatly. The structure factors of tungsten carbide coatings such as tungsten carbide type、 microstructure etc. affected on the properties of the coating directly. While these dependent on spraying process parameters strongly.
The low power plasma spraying technology was in favor of getting tungsten carbide with high hardness and high wear resistance of coating. But related process details were not enough in depth study. The purpose of this study was to search for good parameters of spraying process with high hardness and high wear resistance of coating and research on the microscopic mechanism of ideal organizational structure.
In this paper, the WC coatings were sprayed by low powder plasma equipment,adjusting spraying parameters to preparation WC coating on 42CrMo substrate material. Through metallographic microscope heat treatment organizations of substrate were analyzed. By means of the X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), WC powders and coatings,microstructure and composite were investigated. The effect of spraying process parameters on the WC coatings,structure、density and phase composition was summarized. The formation mechanism of coatings , and on the combination between the matrix and coatings were investigated. Preparing four kinds of coatings under the condition of different voltage , the hardness and abrasion resistance of the coating were studied by the nano-indentation hardness method、micro-hardness instrument and friction and wear test. The results of the study showed that: WC coating was typical layer structure, flat particles mutual stack in together, coating layers with metallurgical combination ,between coating and substrate mainly with machinery combination ,but existing metallurgy combining site. As the spraying power advances , melting WC particles were improving , good effect on flat particles.W2C and CoxWyCz etc. brittle phases appear in WC coating , spraying decarburization phenomenon occurred in the process, the content of them increased along with the increase of voltage, current, power. However, the porosity dropped ,coatings became more density. The pore of WC coating has a great influence on the coating hardness; High hardness, good wear resistance coating was received , when then voltage was from 50V to 55V .The wear mechanism of WC coating was mainly abrasive abrasion. Because of the stress caused by friction, the coating layer bonding was broken and flat particles crack. Brittle fracture occurred in hard grind grain.
Keywords: WC , Plasma spraying, Microstructure, Hardness , Abrasion
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