Friction and wear of TiN-4140 steel couples in methanol

Titanium nitride (TiN) surface layers have the potential to decrease wear and increase the working life of methanol fuel injector components. A number of studies have been conducted on the wear-resistance of TiN in various lubricants. However, the friction and wear characteristics of TiN coatings in a methanol environment have not been investigated. For this research, TiN coatings were obtained by pressure vapor deposition (PVD), chemical vapor deposition (CVD) and ion implantation (ION) processes. The friction and wear characteristics of the TiN surfaces, coupled with a nitrided 4140 steel and in a methanol environment, were determined using reciprocating sliding tests. In general, the coatings protected their substrates from wear, but many caused extensive wear on the 4140 steel sample. The ION layer did not provide adequate wear protection during long-term testing. Wear due to the roughest PVD and CVD coatings increased with applied contact force. The two smoothest PVD coatings exhibited the best tribological performance under the conditions investigated.