Self-lubricating and anti-corrosion amorphous carbon/Fe₃C composite coating on M50NiL steel by low temperature plasma carburizing

Low temperature plasma carburizing was employed to fabricate a carburized layer containing an amorphous carbon/Fe₃C composite coating on the M50NiL steel surface in gaseous acetone. The influence of gaseous acetone content on the carburized layer was investigated by optical microscope, scanning electron microscope equipped with energy dispersive X-ray analyzer, X-ray diffraction, Raman spectroscopy, microhardness tests, pin-on-disc tribometer and anodic polarization tests. A specific carburized layer mainly comprised of carbon expanded martensite (α′_C) with good wear resistance and modest corrosion resistance was formed by plasma carburizing at 550 °C for 4 h. The amorphous carbon/Fe₃C composite coating-containing carburized layer was obtained using gas mixture of acetone (0.3 L/min) and hydrogen (0.2 L/min). The coating showed lowest friction coefficient (about 0.3) and 99.0% reduction in wear rate compared with untreated specimen due to its lubricating effect. Moreover, it showed better corrosion resistance than untreated specimen owing to its chemical inertness. The promising results demonstrated that the improved wear and corrosion resistance could be realized simultaneously by introducing the composite coating with merits of self-lubricating and anti-corrosion.