Highlights

Scuffing in Ceramics

Scientific Achievement

Scuffing, described as sudden catastrophic failure in sliding contacts is one of the most challenging problems in heavily-loaded tribological machine elements such as gears, fuel injectors, bearings, and seals.  Scuffed surfaces essentially lose their functional integrity and hence scuffed components must be replaced. Because of the sudden nature of scuffing onset, significant efforts have been devoted to the understanding and prevention of scuffing.  Unfortunately, the basic mechanism of scuffing is not adequately understood sufficiently to enable prediction of its occurrence or the formulation of prevention strategies.  This study is about scuffing behavior of some structural ceramic materials in sliding contact with hardened steel when lubricated with unformulated poly alpha olefin (PAO) synthetic oil using a block-on-ring contact configuration.  The scuffing resistance of ceramic-on-steel contact pairs is significantly higher than that of steel-on-steel contact pairs under the same test conditions. When macro-scuffing occurs in the ceramic-steel contacts, it always involves extensive transfer of metallic material onto the ceramic surface.  In those instances of limited metal transfer, only micro-scuffing is observed and no scuffing occurs without metal transfer.  Based on these observations, it is proposed that the mechanism of scuffing in metal – ceramic sliding contact pairs is by shear instability between the metal and the metal layer transferred onto the ceramic surface.   

Significance

Results of our study to date identified some of the key mechanisms involved in the scuffing process.  These can form the basis for predictive modeling of scuffing in ceramic materials, which is needed but still lacking.  Some of the results were presented at an international conference (STLE08) and are in press in Tribology Letters.

Performers

M. Cinta Lorenzo-Martin, O.O. Ajayi (Argonne-ES)