Friction and Wear Properties of Spark Plasma Sintering NiCr–SrSO4 Composites at Elevated Temperatures in Sliding Against Alumina Ball

Abstract

Nickel-based self-lubricating composites with SrSO4 as a high-temperature solid lubricant have been prepared by spark plasma sintering method. Their friction and wear properties were evaluated using a high-temperature friction and wear tester in dry sliding against alumina ball up to 600 °C. NiCr–10 wt% SrSO4 composite exhibits satisfactory mechanical properties and tribological properties from room temperature to 600 °C (except for 200 °C) as contrasted with unmodified Ni–Cr alloy. The friction coefficients of NiCr–10 wt% SrSO4 at 400 and 600 °C are 0.32 and 0.20, respectively. The corresponding wear rates are 1.44 × 10−5 and 2.4 × 10−5 mm3/(Nm). The unmodified Ni–Cr alloy exhibits friction coefficients of 0.41 and wear rates in order of 10−4 mm3/(Nm) in a temperature range of 400–600 °C. At elevated temperatures, a dense and protective glaze layer is generated on the worn surface of composites. The glaze layer was then investigated by means of scanning electron microscopy and XPS. Tribo-chemical reaction during high-temperature wear tests is responsible for the formation of the protective glaze layer. The newly formed oxides (NiO and Cr2O3) and some self-lubricating oxysalts (SrSO4 and SrCrO4) can promote the densification of oxide glaze layer, and finally generate a dense lubricating film to effectively reduce friction and wear at elevated temperatures.