Influence of residual porosity on the dry and lubricated sliding wear of a powder metallurgy austenitic stainless steel

Powder metallurgy practices offer the opportunity to control the porosity of steels for tribology applications. The material of interest was an austenitic powder metallurgy stainless steel sintered in a nitrogen atmosphere. Four disc samples with increasing porosity (from 8% to 29%) were subjected to dry and lubricated sliding against an alumina pin using a rotary pin-on-disc tribometer. An estimation based on Hertzian contact analysis has been introduced to define the size of large pores. A normalized scar depth has been defined. The influence of pores on Archard׳s wear law has been analysed. Dry sliding, liquid lubrication, and self-lubrication (filled pores) were all evaluated. During the first few metres of dry sliding, the pores are closed by plastic deformation. After that, the wear rate can be considered the same. In lubricated conditions, pores are not closed and the higher the porosity, the lower the wear rate. In filled-pore, self-lubricated conditions, the sample with the highest porosity showed the lowest wear rate. Reasons for this behaviour are discussed.