Effect of load on tribofilms at the contact interface under dry sliding conditions at 500 °C

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.

Effect of the Normal Load on the Friction and Wear Behaviour of Nickel-based Alloys Ni-Cr-B-Si-C-W

“…From this observation, the increase of the normal load affects differently the behaviour of alloys wear caused by ploughing and abrasive actions, due to the resistance of the alloys related to their microstructure as well as the nature and the distribution of the phases formed which is in line with the work of some authors [20][21][22].…”

“…At the start of the abrasion tests, the hard compounds are brought directly in contact with the second surface, which means that the phases formed in the alloys is due to the positioning of the hard phases of alloy 1 on the outer surface of the matrix (external layer), leading to a direct exposure of friction on the disc, causing an increase of the friction coefficient that quickly stabilises, resulting in minimal wear. The tribofilms formed at the interface have a stable behaviour while providing sufficient protection against accelerated wear [20]. In contrast to alloy 2, which is inside the matrix, they are not directly exposed to the disc, which explains a high and stable coefficient of friction and significant wear.…”

Tribological investigations on tribofilm formation and retention under dry sliding conditions with increasing loads

“…In another similar high temperature pin-on-disc study, conducted on a Nimonic alloy/cast iron tribo-pair, the calculated wear coefficient, for both elements of the tribo-pair, was also found to be of the order of 10 −5 mm 3 /Nm. 34 In general, the disc showed more wear in comparison to the pin, however, the wear coefficients, for both elements of the tribo-pair, correspond to the mild wear regime.…”

Efeito do extrato das folhas da Passiflora edulis na cicatrização da pele

“…A análi-se cromatográfica do extrato hidroalcoólico da P. edulis utilizado neste estudo detectou compostos do grupo das flavonas, dos flavonoides e do ácido ferúlico, tais como epicatequina, rutina, orientina, kaaempferol-3-gal, kaempferol-3-gluc, e kaempferol-3-rut. A epicatequina, um composto antioxidante, apresenta potencial efeito benéfico na cicatrização de feridas (23), porém os mecanismos envolvidos nesse processo não foram completamente elucidados até o momento. O tratamento com epicatequina acelerou a redução do tamanho de feridas, e esse efeito foi aparentemente associado à rápida contração e re-epitelização, processos importantes na proliferação e na migração de células epidérmicas da borda da ferida (24).…”