Wear of ceramics due to thermal stress: a thermal severity parameter

Wear of ceramics under dry sliding conditions is, besides mechanical overload, often governed by frictional heating. On the basis of this study a new thermal severity parameter is introduced and applied to an existing wear map as a function of mechanical and thermal loading introduced by Adachi et al. [Wear 203/204 (1997) 291]. The new map is valid for a wide range of material properties and operating conditions. In this paper, a method is presented to predict the boundary between the mild wear regime and the severe wear regime due to frictional heating. To obtain this, the work of Bos [Frictional heating of tribological contacts, Ph.D. Thesis, University of Twente, Enschede, The Netherlands, 1995] was used to calculate contact temperatures. This model is essentially a fit on numerical calculations, making it possible to include heat partitioning between dissimilar materials while retaining closed form expressions. The stress resulting from the contact temperature can be compared with material properties to obtain the thermal severity of a contact. A new dimensionless thermal severity number, TS, is introduced to determine the thermal severity of a contact. The model has been experimentally justified using measurements of pins of different materials sliding against two types of tetragonal zirconia polycrystal discs. In these experiments it was observed that if the specific wear rate exceeds the value of 3×10−6 mm3/N m, the sliding surfaces were rough and the wear was regarded as severe. This criterion is closely related to the criterion based on the ratio of process surface roughness over mean grain size Adachi et al. [Wear 203/204 (1997) 291].