Oxygen diffusion enables anti-wear boundary film formation on titanium surfaces in zinc-dialkyl-dithiophosphate (ZDDP)-containing lubricants

 This paper reports a wear reduction by up to six orders of magnitude for Ti-6Al-4V alloy when treated by an oxygen diffusion (OD) process and subsequently tested in a zinc-dialkyl-dithiophosphate (ZDDP)-containing lubricant. In addition to case hardening, it is discovered that OD enables the formation of an anti-wear boundary film on the titanium surface. Transmission electron microscopy and surface chemical analyses revealed that this boundary film has a two-layer structure comprising an amorphous oxide interlayer and a ZDDP-based top film with complex compounds.