Tribological Properties of Plasma-Sprayed NiAl–Ag–Ta–Cr₂O₃ Composite Lubrication Coatings from Room Temperature to 750 °C

Abstract

With the rapid advances in science and technology, the core parts and techniques in tribosystems rely on solid-lubricating materials at wide temperature ranges for durability, especially for designing and producing materials with low friction coefficient and high wear resistance over wide temperature ranges. In this paper, a series of NiAl-Ag-Ta-Cr₂O₃ composite coatings with different contents of Ta and Ag were deposited by plasma spraying, and their tribological properties at RT-750°C under dry sliding conditions were investigated by a ball-on-disk tribometer. The friction products and compositions of worn surfaces at different temperatures were investigated. The deposited NiAl-Ag-Ta-Cr₂O₃ composite coatings exhibited excellent wear resistance at RT (10⁻⁷ mm³/Nm), while the friction coefficients were lower than 0.5 at RT to 750°C. The contents of Ta and Ag determined the mechanical properties of coatings and greatly affected the tribological properties by creating a tribo-film (lubricant film and glaze layer). NiAl-10Ag-5Ta-20Cr₂O₃ coating shows better tribological properties under all temperatures, while the wear rate is reduced to 5.58·10⁻⁶ mm³/Nm at 750°C, and the friction coefficient falls to 0.21 at 600°C. Excellent lubrication and wear resistance of composite coatings at high temperatures is mainly attributed to the Ag acting as the lubrication phase, and the top surface of the wear track being covered with a smooth glaze layer, which consisted of Ag, Ta₂O₅ Cr₂O₃, and AgTaO₃. In addition, the lubrication mechanism of silver tantalate was also briefly discussed.