The Tribological Performances of the Boron Carbide Films Tested under Wet Air and Wet N2 Conditions
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In the previous literatures, the friction reduction of boron carbide (B4C) with the increasing relative humidity was mainly attributed to the formation of boric acid during the friction tests. In the present investigation, however, low friction coefficient was obtained under wet air (85% RH) without the formation of boric acid, suggesting that there is another low friction mechanism. Furthermore, low friction coefficient was also achieved under wet N2 (85% RH, without O2) without the formation of boric acid, implying that the core factor for the friction reduction is water vapor rather than oxygen. Therefore, we infer that the adsorption of H2O on the passivated boron carbide surface is the main reason for the reduction of friction coefficient. It should be noted that friction coefficients under wet air were lower than that under wet N2, which demonstrates that O2 plays a secondary role to reduce friction coefficient.
KeywordsBoron carbide film Wet air Wet N2 Passivation A nanoscale water layer
The authors are grateful for the financial support from the National Key R&D Program of China (No. 2018YFB0703801) and the National Natural Science Foundation of China (No. 51775535).
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