Effect of load on tribofilms at the contact interface under dry sliding conditions at 500 °C: Einfluss der Last auf tribologische Schichten an der Kontaktfläche unter Trockenreibung bei 500 °C

Authors: Saleem, S.S. and Wani, M.F.

Journal: Materialwissenschaft und Werkstofftechnik

Volume: 49

Issue: 2

Pages: 169-184

eISSN: 1521-4052

ISSN: 0933-5137

DOI: 10.1002/mawe.201700108

Abstract:

This paper presents a study of the effect of load on the retention of the tribofilms formed at the interface of a dry sliding contact between exhaust valve material, Nimonic alloy (N 80A) and valve-seat material, ductile cast iron (GGG-40), at a temperature of 500 °C. The role of tribofilms in influencing friction and wear behaviour at elevated temperature is highlighted. Reciprocating pin-on-disc experiments were conducted using a hemispherical shaped pin sliding against a flat disc at 20 Hz oscillating frequency, 2 mm stroke at loads of 20 N to 50 N. Low coefficient of friction, in the range of 0.13 to 0.15, was observed at loads up to 40 N whereas at a load of 50 N, the average coefficient of friction increased to 0.29. Optical and scanning electron micrographs with energy dispersive spectroscopy analysis indicate evidence of formation and retention of well compacted and strongly adhering tribofilms at loads up to 40 N. At 50 N, even though more abrasive wear is seen, initial deterioration and subsequent reforming of the tribofilms with increasing sliding time is observed. Overall, more wear was observed for the valve-seat material as compared to the valve material. Raman spectroscopy primarily indicates the presence of hematite on the worn surfaces at loads of 20 N to 40 N, whereas magnetite presence is strongest at the highest load of 50 N. Increase in tribofilm hardness was observed with increase in contact load whereas the thickness of the tribofilm was not significantly affected by the contact load.

Source: Scopus