The influence of temperature on friction and wear of unlubricated steel/steel contacts in different gaseous atmospheres

• At 200 °C in all anaerobic gases (AG) friction and wear were lower than in air.
• In AG at 200 and 20 °C friction and wear were lowest in CO2 followed by N2 and Ar.
• At 200 °C in N2 and CO2 deterioration of beneficial tribolayer properties occurred.
• In Ar less Fe–Fe bonded at 200 than 20 °C decreasing wear which elsewhere increased.

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 (N2) and carbon dioxide (CO2), 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 CO2 atmosphere; they were slightly higher in N2 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 N2 and CO2 atmospheres, XPS analyses of the wear debris showed an increased concentration of non-carbidic carbon and furthermore for the CO2 atmosphere, iron–carbon–oxygen layers were also found which probably provided the very favourable friction and wear properties observed in this atmosphere. In N2 and CO2 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 N2 and CO2-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.

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