Effects of sliding velocity and normal load on the tribological behavior of a nanocrystalline Al based composite

Nanocrystalline Al based composite containing 39 vol.% AlN nanoparticles with enhanced mechanical properties was subjected to friction and wear characterization under various conditions. It is interesting to found that an oxygen-rich tribolayer was formed at all sliding speeds and normal loads, which seems to control the tribological behavior of the composite to a large extent. Friction coefficient of the composite increases with the increase in sliding velocity, while the wear rate decreases in a hyperbolic trend. The improved wear resistance at higher velocity was attributed to increased tribolayer coverage on the worn surface, and the enhanced tribo-oxidation. Increase in the applied load leads to steady reduction of the friction coefficient, and slight variation of the wear rate in load range of 5-25 N. In this range, tribolayer is the most import feature on worn surface, and wear occurs mainly by delaminating within the tribolayer. Whereas, when the load increases up to 35 N, both the friction coefficient and wear rate steeply increase up to high values, indicating a severe wear. At this load, tribolayer only covers small part area of worn scar, and delamination happens within the composite underneath the tribolayer.