J. Schofer et al., Formation of tribochemical films and white layers on self-mated bearing steel surfaces in boundary lubricated sliding contact, WEAR, 248(1-2), 2001, pp. 7-15
Formation of tribochemical layers and microstructural surface alterations d
uring mild reciprocating sliding wear of AISI 52100 steel were studied unde
r boundary lubricated conditions using a non-additive hydrocarbon lubricant
. At the onset of relative motion no friction-induced chemical processes co
uld be detected due to the protecting natural oxide film on the contacting
steel surfaces. After a few sliding cycles, chromium carbides were pulled o
ut of the ball surface leading to removal of the protecting layers and to t
he initiation of fast tribochemical reactions on the contact area. After ab
out 1000 sliding cycles, so-called white layers developed on the ball surfa
ce showing greater carbon contents and hardness than the bulk material. Thi
s white layer formation could be attributed to high local pressures and sub
sequent grooving of the surface by wear debris. It was shown that the lubri
cant acted as a carbon donor owing to the adsorption of cracked hydrocarbon
molecules on the steel surface. Adsorbed carbon atoms diffused into the bu
lk material and promoted the mechanically-induced phase transformation to t
he white layers. (C) 2001 Elsevier Science B.V. All rights reserved.