Dry sliding wear of ferrous PM materials

Ashbyʹs map for dry sliding wear of wrought steels has been used as a guide to interpret the dry sliding wear behaviour of PM materials. It has been shown that this map is useful in understanding the acting wear mechanisms and also the experimental wear rates. For given tribological conditions, in terms of normalised pressure and sliding velocity, the sliding wear resistance of PM materials is similar to that of wrought steels, although a closer look at the experimental results highlights the peculiar role of porosity and of a heterogeneous microstructure. In particular, materials with a porosity content of about 10% and with an homogeneous microstructure display the best performances. Since mild wear in metals can be obtained through the formation of protective oxide glazes, steam treatment turned out to be a natural way of increasing the sliding wear resistance of PM ferrous materials. The ʹsurface durabilityʹ of steam treated materials was thus shown to depend on the quality of the layer, the applied load and the nature of the counterface. The role of the counterface and the opportunity to adopt other surface treatments to increase the sliding wear resistance of PM ferrous materials are also discussed.