Ecologically friendly, vegetable-oil-based, self-generating, self-healing amorphous carbon (a-C) tribofilms were spontaneously formed on steel using no harmful additives. a-C films are desirable for manufacturing, automotive, and aerospace applications because they reduce energy costs and prevent component wear. Self-forming a-C films adhered onto steel during reactions of vegetable oils at elevated temperatures and pressures. For the first time, a chemical mechanism for tribofilm formation has been established. The initial step forms poly(triacylglyceride) on the steel surface. Next, a hydrogenated amorphous carbon network (a-C:H) forms. Then, the network dehydrogenates to form a-C. And eventually, it forms nanocrystalline graphite (ncG) just before the oil catastrophically fails. By understanding the complete reaction mechanism, it has been possible to create a-C tribofilms from vegetable oils without toxic additives and without involving mineral oils in the formulations, opening the prospect of greener lubricant technologies for the future. In addition, the vegetable oil formulations matched and often outperformed their mineral-oil-based counterparts.
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