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

Abstract

• NiCr matrix composites with WS 2 as lubricant suffer severer wear degradation at high temperatures • NiCr-WS 2 -Ti composite with heterostructure is prepared by spark plasma sintering. • The composite NiCr-WS 2 -Ti exhibits low friction coefficient and high wear resistance at elevated temperatures • Ti is preferentially oxidized, forming abundant TiO 2 protrusions and constructing in situ a special surface texture. • By controlling oxidation and surface texturing, a protective glaze layer formed at surface, leading to excellent tribological properties 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-WS 2 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 TiO 2 protrusions and microdimples on the surface, i.e. in situ surface texturing. Besides, TiO 2 was of high chemical activity and readily to react with other oxide debris during high temperature sliding process to form compounds of NiTiO 3 and CrTi 2 O 5 . 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-WS 2 -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 mm 3 N −1 m −1 , accounting for only 2.7% of that of NiCr-WS 2 composite.