Argonne National Laboratory, Lemont, Ill., announces that a research team has developed a self-lubricating diamondlike carbon tribofilm that regenerates itself by breaking down the molecules of lubricating oil and rebuilding the tribofilm as it is worn away. Tests also revealed that the DLC tribofilm reduced friction by 25 to 40%, and that wear was reduced to unmeasurable values.
“This is a very unique discovery, and one that was a little unexpected,” says team leader Dr. Ali Erdemir in a massive understatement. “We have developed many types of diamondlike carbon coatings of our own, but we’ve never found one that regenerates itself by breaking down the molecules of the lubricating oil, actually rebuilding the tribofilm as it is worn away.”
The original discovery occurred when Dr. Erdemir and Dr. Osman Levent Eryilmaz decided to see what would happen when a small steel ring was coated with a catalytically active nanocoating, then subjected to high pressure and heat in a base oil without the complex additives of modern lubricants. When they looked at the ring after the endurance test, they did not see the expected rust and surface damage, but an intact ring with an odd blackish deposit on the contact area.
“This test creates extreme contact pressure and temperatures, which are supposed to cause the ring to wear and eventually seize,” said Dr. Eryilmaz. “But this ring did not significantly wear, and this blackish deposit was visible. We said, ‘This material is strange. Maybe this is what is causing the unusual effect.'”
Looking at the deposit under high-powered optical and laser Raman microscopes, the scientists realized the deposit was a tribofilm of diamondlike carbon, similar to several other DLCs developed at Argonne in the past. But it worked even better. Tests revealed the DLC tribofilm reduced friction by 25 to 40%, and that wear was reduced to unmeasurable values.
Further experiments showed the coatings interact with the oil molecules to create the DLC film, which adheres to the metal surfaces. When the tribofilm is worn away, the catalyst in the coating is re-exposed to the oil, causing the catalysis to restart and develop new layers of tribofilm. The process is self-regulating, keeping the film at consistent thickness.
http://www.anl.gov/articles/argonne-discovery-yields-self-healing-diamond-carbon
