Dry sliding friction and wear behaviour of hybrid AA7075/Si3N4/Gr self lubricating composites

The present investigation aims to study the effect of graphite on the friction and wear behaviour of AA7075/Si3N4 composites. Four different sample compositions have been fabricated by stir casting technique. The percentage of silicon nitride has been fixed as 8 wt% and the percentage of graphite has been varied from 0-6 wt%. The cast composites have been tested for microhardness and density prior to the tribological testing. Unidirectional friction and wear testing has been carried out for all compositions under five different loading conditions. Moreover, in order to elucidate the effect of speed on the tribological behaviour testing at 4ms(-1) and 7ms(-1) has also been carried out. SEM analysis has also been carried out for morphological analysis of the worn surfaces. A decrease in microhardness and density of the composites is observed with an increase in graphite wt% in the base alloy. The addition of graphite led to a linear decrease in the COF. However, the wear loss exhibited a decreasing trend till 4 wt% graphite and thereafter it increased. The increase in the normal load led to an increase in COF as well as wear loss. The increase in the sliding speed led to an increase in the wear loss, however the COF exhibited a decreasing trend with an increase in speed. The SEM images revealed that the addition of graphite resulted in a decrease in the abrasive wear. Mild delamination and smoother surfaces were observed for higher content of graphite. The fabricated self lubricating composite could serve various anti-wear and antifriction applications particularly in automotive sector.