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 metal s after some time of sliding is a well known phenomenon. However, few models have been presented to account for such a transition. In this p aper, a mathematical model, based on experimental observations that th e transition is caused by the development of wear protective layers on the rubbing surfaces, is proposed. The protective layers are develope d mainly from accumulated wear debris particles retained within the we ar tracks; these can have various characteristics, depending on the ex perimental conditions and the properties of the metal, particularly th e oxidation conditions and the contact between the rubbing surfaces. T here is broad agreement between reported experimental observations and calculated predictions based on this model. For example, the developm ent of protective layers occurs very quickly once the transition time/ distance has been attained; whether or not 'glaze' layers develop on t op of the compact particle layers depends on the sliding temperature, leading to the concept of a transition temperature. Wear debris partic le 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 transi tion becomes difficult, or even impossible. The model is applicable to both room temperature and elevated temperature sliding wear.