| With the development of the aviation industry, gears often operate under extreme conditions of high contact loads and high speeds, and their surface working temperature exceeds 350°C, which requires higher performance of gears than before. Although thermal chemical treatments are still the main method to strengthen the surface of the gear, many modern surface technology is gradually applied to the gear and shows very attractive prospects.In the paper, in order to improve the surface hardness and wear resistance of the gear steel, the W-Mo coating was formed onto the 16Cr3 NiWMoVNbE gear steel by using double-glow plasma surface metallurgy technique. In contrast, the gear steel was also treated by pack carburizing to produce the carburizing strengthening layer.By research the influence of process parameters on the coating's thickness and quality, the optimum parameters are obtained and as below: source voltage 950~1000V, substrate voltage 550~600V, temperature 850~870?, working pressure 36 Pa, holding time 3.5h, and distance between the source and substrate 20 mm. Under the optimum parameters, the formed W-Mo coating is continuous and compact and is well bonded to the gear steel. The total thickness of the coating is about 12?m. XRD shows that the coating is mainly composed of W and Mo phases. The micro-hardness test shows that the W-Mo coating has the highest hardness, about 1073.42HV0.05, which is nearly 2.95 times greater than that of the substrate sample and is nearly about 1.68 times greater than that of the pack carburizing sample.The rotating wear testing machine is used to study the influence of temperature on the wear resistance of samples. Results show that the W-Mo coating exhibits the smallest wear volume under different temperature. Three samples are all experienced severe oxidation in 350?. The severe oxidation wear is occurred on the surface of the substrate sample and the pack carburizing sample. Whereas the W-Mo coating forms a compact oxide film of W and Mo that has a certain anti-friction effect. Besides, in the high temperature of 500?, the hardness of the substrate sample and pack carburizing sample is decreased, which causes more serious wear than in 350?.The reciprocating wear testing machine is used to investigate the influence of the load, sliding velocity and friction pair on the wear resistance of samples at room temperature. Results show that the W-Mo coating both exhibits the best wear resistance under different condition. In the highest load of 620 g, the wear volume of the W-Mo coating is about 42.4% of pack carburizing sample and is only about 15.4% of the substrate sample. In the highest speed of 6m/min, the wear volume of W-Mo coating is about 40.5% of pack carburizing sample and is only about 16.6% of the substrate sample. Although the wear volume of three samples that are slided by the Si3N4 friction pair is all higher than the sample that are slided by the GCr15 friction pair, the W-Mo coating still shows the lowest wear volume. |
PDF Full Text Request