Improving high-temperature wear resistance of NiCr matrix self-lubricating composites by controlling oxidation and surface texturing

Abstract

Self-lubricating composites (SLCs) are widely used in the fields of aerospace and marine, but the conventional NiCr matrix SLCs with sulfide as solid lubricant often suffer from low wear resistance at high temperatures. In view of its high affinity with oxygen and also the high oxidation rate, appropriate amount of nano Ti was added to NiCr-WS₂ composites prepared by spark plasma sintering (SPS) to adjust the oxidation behavior and surface texture. When exposed to high temperature, Ti was preferentially oxidized in comparison to Ni and Cr, resulting in abundant TiO₂ protrusions and microdimples on the surface, i.e. in situ surface texturing. Besides, TiO₂ was of high chemical activity and readily to react with other oxide debris during high temperature sliding process to form compounds of NiTiO₃ and CrTi₂O₅. The high chemical activity of oxide debris that was conducive to sintering, combining with the special surface texture that stores as many wear debris as possible, promoted the rapid formation of a protective glaze layer on the sliding surface. The NiCr-WS₂-Ti composite exhibited low friction coefficient but high wear resistance at elevated temperatures. Especially at 800 °C, it presented a wear rate of as low as (2.1 ± 0.3) × 10⁻⁵ mm³ N⁻¹ m⁻¹, accounting for only 2.7% of that of NiCr-WS₂ composite.