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The influence of temperature on friction and wear of unlubricated DIN 100Cr6 steel/steel contacts was studied in different anaerobic gaseous atmospheres, namely argon (Ar), nitrogen (N 2 ) and carbon dioxide (CO 2 ), and air atmosphere was used as benchmark. Tribological experiments were performed at high temperature (200 °C) and the results were compared with previously published results from experiments performed at ambient temperature (20 °C). Reciprocating ball-on-disc tribological tests were conducted with high contact pressures (maximum initial contact pressure of 1.5 GPa). In all anaerobic gas atmospheres at high temperature, lower friction and wear were measured than in air atmosphere. The lowest friction and wear were measured in CO 2 atmosphere; they were slightly higher in N 2 atmosphere and even more slightly higher in Ar atmosphere. In all anaerobic atmospheres, different oxidation kinetics of steel surfaces occurred as compared with air atmosphere. For N 2 and CO 2 atmospheres, XPS analyses of the wear debris showed an increased concentration of non-carbidic carbon and furthermore for the CO 2 atmosphere, iron–carbon–oxygen layers were also found which probably provided the very favourable friction and wear properties observed in this atmosphere. In N 2 and CO 2 atmospheres, higher wear and friction were observed at high temperature than at ambient temperature, which indicates that at high temperature, a deterioration of the beneficial properties of the N 2 and CO 2 -reacted tribolayers occurred. On the contrary, in Ar atmosphere at high temperature, a decreased adhesion and a significantly lower wear as compared with ambient temperature was observed. [ABSTRACT FROM AUTHOR]

It is generally known that gaseous atmospheres can significantly affect the friction and wear behaviour of non-lubricated contacts; however there still exists a lack of knowledge on the subject, since the tribological behaviour and the tribochemistry of the gas-lubricated systems are highly sensitive to the selection of the operating parameters, and the results from available literature are often scattered and sometimes even contradictable. This study was focused on the identification of the friction and wear mechanisms of technical gases used at atmospheric gas-pressure in non-lubricated DIN 100Cr6 (AISI 52100) bearing steel contacts at severe operating conditions (high-frequency oscillation at high contact pressure). Argon (Ar), nitrogen (N 2 ) and carbon dioxide (CO 2 ) were used as gas atmospheres and air atmosphere was used as a reference. The gases are analysed in terms of their chemical reactivity with the steel surfaces and a correlation between the properties of different tribochemical products and the observed friction and wear mechanisms is made. In N 2 and CO 2 atmospheres, wear was significantly lower than in air atmosphere, with a wear reduction comparable to the effect of using a liquid lubricant. In N 2 atmosphere, a slightly higher friction was measured than in air atmosphere, while in CO 2 atmosphere, friction was 60% lower than in air atmosphere. In Ar atmosphere, both friction and wear were slightly higher than in air atmosphere. With X-ray photoelectron spectroscopy (XPS) of the wear particles, it was observed that the concentrations of different tribochemical products and their mutual ratios critically determine the friction and wear behaviour of the non-lubricated steel contact. [ABSTRACT FROM AUTHOR]