Investigation On Tribological Performance Of P/M Ni-Co-Al High-temperature Alloy

With the development of high-tech industries such as aviation, aerospace etc., the requirement on materials which works under harsh conditions is increasing. In recent years, the high-temperature tribological performance of materials is becomeing the hot points in the international research field. The Ni-base superalloys are the widely used materials in the field of aviation, however, the research on the tribological performance of Ni-base superalloys is not yet abundant. In this article, the tribological behaviors of Ni-Co-Al alloys prepared by powder metallurgy (mechanical alloying and hot-press sintering) were investigated, and the influence of hot-press sintering temperature on tribological performance of Ni-Co-Al alloy was studied, and the effects and mechanisms of Al and Co content on the tribological properties were also elucidated. Through the observation of the wear surface morphology and the analysis of wear scars, the tribological mechanisms were explained.The results show that a Ni-1OCo-Al alloy prepared by powder metallurgy is mainly composed of y, y’and a small amount of Al2O3. γ’ dispersed in the y matrix. The hardness, compressive strength of the alloys increase with the increase of hot-press sintering temperature, while these properties change little when the sintering temperature up to1200℃. As the sintering temperature increases, the tribological performance of the alloy at800℃gets better. Through the analysis of worn surfaces, a glaze-like oxide scale formed on the worn surface, which seemed to be beneficial for the tribological performance. The adhesive strength between the oxide scale and the substrate affects the tribological performance of the alloy, which may be related to hot-press sintering temperature. Moreover, hot-press sintering temperature improves the hardness, which also relieves the abrasive wear.As to the same Co content Ni-Co-Al alloy, raising the Al content can enhance the hardness, increase the frictional coefficient and reduce the wear rate at room temperature. While at800℃, the frictional coefficient elevates with the increase of the Al content, and the wear rate changes little. The tribological property of the alloys at800℃gets worse, compared to the RT tribological property.The appropriate Co content can improve the hardness and compressive strength of Ni-Co-Al alloys, and with the rise of Co content, the tribological properties get better, however, these properties get worse when the content of Co reaches30wt.%."Glaze" oxide layers form on the worn surface, which is composed of soft oxide CoO and others. Through the observation and analysis of worn surfaces, it can be found that the composition and the shedding extent of the oxide "Glaze" is responsible for the high temperature tribological properties.