Self-lubrication of Cl-implanted titanium nitride coating for dry metal forming

Various kinds of lubricants are utilized in every aspect of manufacturing for mass production. To prolong the life time of tools or dies, much amount of lubricants must be used for mechanical machining or metal forming, resulting in massive emission of wasted lubricants. Dematerialization in the environmentally benign manufacturing requires less use and less emission of lubricants as possible to significantly reduce the environmental burden. For that purpose, dry machining or dry metal forming becomes a challenging issue to be solved. In the present paper, new tribological coating design is proposed to significantly reduce the wear volume and friction coefficient and to minimize the emission of wastes in wear. Titanium nitride coating has been widely used for protection of dies and tools from severe wear. Due to high friction coefficient and less wear endurance, adhesive wear often takes place against the stainless steel or ductile metallic alloy counter parts. Hence, even using this type of protective coating, lubricants are indispensable to reduce the friction coefficient and to be free from metallic sticking. Self-lubrication mechanism can be imprinted into titanium nitride coating only by chlorine implantation into it. Under the presence of chlorine in the wear track, the plastically deforming intermediate oxide film is in-situ formed to sustain low friction and low wearing mode in the relatively wide range of normal pressure and sliding velocity on the contact surface. Through the feasibility study, total amount of chlorine used for this self-lubrication is found to be negligibly small, but the self-lubrication mechanism is sustained to be working until the initial titanium nitride coating is completely worn out from the substrate.