Tribo-layer Properties on AISI52100 Lubricated by Palm Methyl Ester Containing Graphene Nanosheet

The demand for bio-degradable lubricants has been increasing nowadays due to concerns on pollution free environment. Vegetable oil-based lubricant is one of promising sources of lubricant that can fulfill the requirement, especially when combined with eco-friendly nanomaterial additives. On the other hand, tribo-layer formation as the mechanism of friction and wear reduction in a tribo-pair has been generally accepted in tribology field. The tribo-layer layer can be formed due to the tribo-chemical reaction during friction process and its formation can be enhanced with incorporation of nanomaterials as additive. In this study, the tribo-layer characteristics formed on self-mated AISI52100 contact pair were investigated. The contact pair were lubricated by two kind of lubricant's specimens, i.e. palm methyl ester (PME) and palm methyl ester containing graphene nanosheet additive. It is found that in the case of palm methyl ester without graphene additive, the tribo-layer comprises oxidative layer of Fe and O elements. With the presence of graphene nanosheets in the lubricant, the tribo-layer was formed in a comparatively wider contact area. Carbon element was more observable in the layer besides oxygen, emphasizing the role of graphene nanoparticles. In both cases, the friction coefficient and wear are relatively similar.