On the interdependence between kinetics of friction-released thermal energy and the transition in wear mechanisms during sliding of metallic pairs

Sliding of complying solids is often associated with the release of thermal energy. This energy accumulates within the mechanically affected zone (MAZ) of the rubbing pair. The accumulation of thermal energy within the MAZ tends to maximize the potential energy at the interface. Now, since a maximized potential energy renders the sliding system unstable, one (or both) materials will respond in a manner that consumes (dissipates) part or all of the accumulated energy in order to re-establish system stability or at least equilibrium. The material response may be in many forms: oxidation, crack initiation, wear debris generation, transition in wear mechanism, etc. As such, one may consider that these processes are intrinsic responses by the material to dissipate energy. Moreover, many of these responses are triggered at different stages of rubbing according to the balance between the rate of external thermal energy release (which is a factor of the nominal operation parameters) and the rate of thermal energy accumulation—RTEA (which is mainly a function of thermal transport properties of the rubbing pair). An interesting feature of this view is that the later quantity—RTEA—is directly related to the ability of the particular solid to dissipate thermal loads. This quantity, which is termed here as the heat dissipation capacity (HDC), is directly related to the state of blockage of energy dissipation paths within the rubbing solid. The objective of this paper is therefore to study the relation between the change in the HDC of a sliding solid and the transition in the mechanism of wear. It is shown that there exists an inverse correlation between the change in the HDC and the transition in the mechanism of wear. Moreover, it is also shown that a so-called ratio of residual heat (RRH, representing the ratio between the actual thermal load and the part of that load that is not dissipated by the solid) is a significant parameter that influences the magnitude and mechanism of wear. The findings are applied to explain the wear behavior of two tribo systems: a titanium (Ti-6Al-4V) sliding on itself and sliding on a steel (AISI M2) counterpart.