A MATHEMATICAL-MODEL FOR SLIDING WEAR OF METALS AT ELEVATED-TEMPERATURES

The transition in wear rate from a high value to a low value for metals after some time of sliding is a well known phenomenon. However, few models have been presented to account for such a transition. In this paper, a mathematical model, based on experimental observations that the transition is caused by the development of wear protective layers on the rubbing surfaces, is proposed. The protective layers are developed mainly from accumulated wear debris particles retained within the wear tracks; these can have various characteristics, depending on the experimental conditions and the properties of the metal, particularly the oxidation conditions and the contact between the rubbing surfaces. There is broad agreement between reported experimental observations and calculated predictions based on this model. For example, the development of protective layers occurs very quickly once the transition time/distance has been attained; whether or not 'glaze' layers develop on top of the compact particle layers depends on the sliding temperature, leading to the concept of a transition temperature. Wear debris particle size plays an important role in determining the wear transition; if the particles are too large and/or are difficult to fragment, such as those generated when the load or speed are high, they are more likely to be removed from the wear tracks and the severe to mild wear transition becomes difficult, or even impossible. The model is applicable to both room temperature and elevated temperature sliding wear.