Influence of temperature on the tribo-performance of GGG-60 seat insert against 23–8 N exhaust valve steel

Abstract

The aim of this study is to assess the feasibility of 23–8 N steel as a valve material with GGG-60 seat insert by investigating the influence of temperature on its friction-wear behaviour. Reciprocating tests were performed on the tribo-pair under 20 N load and at temperatures of 50 °C, 100 °C, 200 °C, 300 °C, 400 °C and 500 °C. For all temperatures, the coefficient of friction (COF) shows a declining behaviour as the test progressed with a salient run-in behaviour. The average value of COF increases with temperature up to 300 °C (0.251), beyond which a decreasing trend can be observed. The decrease in friction coefficient at higher temperatures is attributed to the formation of glazed layers at elevated temperatures. A similar behaviour is observed for the specific wear rate, with the highest value attained at 300 °C (1.929 × 10−5 mm3/Nm). Presence of harder particles of Fe3O4 and α-Fe2O3 in the scar is confirmed using Raman spectroscopy, which results in an increased wear of GGG-60. A significant reduction in the value of specific wear rate of GGG-60 is observed at the temperature of 500 °C. The lower value of specific wear rate at 500 °C is attributed to the formation of tribo-film, which is confirmed by SEM micrograph. Effective tribological performance at elevated temperatures indicates the suitability of application of the tribo-pair as exhaust valve-seat arrangement.