Wear of particulate metal matrix composites

Particulate reinforcing phases in metal-matrix composites (MMCs) can provide resistance to both sliding wear and abrasion by protecting the softer metallic matrix. In this review, the wear behavior of particulate MMCs in dry and lubricated sliding, and also under conditions of abrasive wear, is discussed. Stable tribological performance can be achieved under conditions of mild sliding wear. While wear rates normally reach an equilibrium (or steady state) in the mild wear regime, accelerated wear rates (with sliding distance and load) are observed in the severe wear regime due to large scale plastic deformation, and in some instances, local melting of the surface layers. MMCs can show significantly lower wear rates compared to unreinforced alloys over a substantially wider range of pressure and sliding speed. Wear mechanism maps are effective ways of delineating the regimes of dominant sliding wear mechanism (oxidation, delamination, seizure etc.) and show the effect of frictional temperature on wear transitions. The very small wear rates observed in lubricated sliding define a new wear regime different from mild and severe wear not only in terms of the infinitesimal rate of material removal but the mechanisms of material removal involved are also different. Tribolayers that form during the running in period are responsible for the very low wear rates observed in this ultra-mild wear regime. Reinforcement can also provide excellent improvements in resistance to low-stress abrasive wear. However, major enhancement of wear resistance in the severe sliding wear regime, or to high-stress abrasion, cannot be expected from these composites