Research On The Characteristics Of Low-power Plasma Spraying Tungsten Carbide

Tungsten carbide is widely applied in industry for its causticity and high rigidity and rupture tenacity. Thermal spray technology is the main way of producing tungsten coatings. Although good tungsten carbide coatings can be prepared by high velocity oxy-fuel gas flame spraying (HVOF) and explored spraying, the gas was greatly consumed, so the price of spraying is very expensive and the pollution is very heavily, while the equipment of explored spraying is also expensive, occupying large space and the noise is loud too, which result in the difficulties of spraying work. For traditional plasma spraying technology which applying an externally-fed powder system, the power consumption is large, and the powder deposit rate is very low. Additionally, tungsten carbide coatings sprayed by tradition plasma spray method decomposed heavily, which resultes in the decreasing hardness and wearability. The low power plasma spraying equipment (plasma-LE15) use in the experiment was developed by Dalian Maritime University Prof.Gao Yang, compared with plasma spraying using an external-fed powder system, the spray power is lower, but the efficiency is higher and the operation is facility. Based on it, studying the microstructure and properties of the coatings produced by low power plasma spraying is necessary, which can also expand the application of low power plasma spray in industry.In this paper, the influences of gas composition on decomposing of tungsten carbide coatings was investigated, microstructure and properties of different tungsten carbide coatings and the coatings sprayed by coarse and fine WC-Co powder was analyzed. The powder particle spherical in plasma jet and the powder particle flattening on the base were observed. Additionally, the influences of Ï„_T and Ï„_i on melt of the powder particle in plasma jet were investigated. The Conclusions are stated as below:1. In Ar-H₂ plasma spraying, decomposing of tungsten carbide is much more heavier than that in Ar-N₂ plasma spraying. Among different tungsten carbide coatings (WC-NiCr, WC-Co, WC-CrCo) sprayed under the same condition, coatings ofWC-Co decomposed less, and hardness of WC-NiCr coatings is the lowest one. In the WC-Co coating, by increasing of the coating thickness, decompose of tungsten carbide decreases but hardness of the coating increased. WC-Co coating with finer powder spraying tungsten carbide decomposed into tungsten in such condition.2. In 130A/70V condition, the spherical of powder particle in plasma jet is very sufficient. In 130A/70V condition the particle flattened on the base. The results of researching on xT indicated that the granularity is smaller and the powder was heated better. The calculating result of Xj showd that the Xj value of tungsten carbide is bigger than one of metal powder, which proved the surface temperature and center temperature of the particle have a great difference.3. In 130A/70V condition the coatings produced with WC-Co powder of granularity 50⁸0nm have a better mechanic property than one of the coatings produced in 130A/40V condition..