Abstract
The in-situ formation of oxides on alloy surface induced by high temperature can effectively reduce wear and resist oxidation. In consideration of the solid solution strengthening effect and great oxidation resistance of additional elements at elevated temperature, the NiCrWMoCuCBFe coating was prepared by high velocity oxygen flame (HVOF) spraying technology, and its tribological behavior was scrutinized from 25 to 800 °C. By means of high temperature Vickers hardness tester and high temperature X-ray diffractometer, the mechanical properties and microstructures of NiCrWMoCuCBFe coating were measured. And the effect of the mechanical properties and microstructures of the coating on tribological performance was discussed in detail. The results showed both its friction coefficient (0.37) and wear rate (5.067 × 10−6 mm3·N−1·m−1) at 800 °C were the lowest, which was mainly related to the formation of “glaze” layer on the coating surface at high temperature. The glaze layer consisted of two parts, which were NiCr2O4 oxide film with the ability of interlaminar slip formed in the outer layer and nano-grains existed in the inner layer. Worth mentioning, these nano-grains provided bearing capability while the oxide film was vital to reduce wear rate and friction coefficient. As the ambient temperature increased, many hard oxides were produced on the wear scars, including NiO, Cr2O3, MoO3, and Mo2C. They can improve tribological and mechanical properties of NiCrWMoCuCBFe coating at a wide temperature range.
Highlights
There are numerous mechanical components serving at high temperature applications, such as high-temperature bearings, valves, and hot end parts of gas turbines
Taking full account of the wear reduction mechanism of the common solid lubricant used in high temperature, many researchers found that both the direct addition of solid lubricant and in-situ formation of solid lubrication film with low shear strength could effectively improve tribological performance of the material in elevated temperature [1,2,3]
Given the two major factors affecting the tribological property of materials at high temperature: the oxidization behavior and the stability of mechanical properties, in-situ formation of oxide film induced by temperature could effectively improve tribological properties
Summary
There are numerous mechanical components serving at high temperature applications (energy exploration, mechanical metallurgy, aerospace, and many other fields), such as high-temperature bearings, valves, and hot end parts of gas turbines. They need to withstand the severe oxidation and degraded mechanical properties caused by high temperature, and should have excellent resistance to deal with tribological issues during service. Given the two major factors affecting the tribological property of materials at high temperature: the oxidization behavior and the stability of mechanical properties, in-situ formation of oxide film induced by temperature could effectively improve tribological properties. The Co-enriched oxides were more favorable to form a dense lubricating glaze layer to reduce the wear rate, and decrease the friction coefficient
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