Assessment of the tribolological behavior of a metallic tribopair: LM25 alloy-Si3N4 composites against EN 31 steel

Abstract

In the present research work, tribological behavior of hard ceramic silicon nitride (Si3N4) reinforced aluminium alloy LM 25 based composites against EN 31 steel in ambient conditions at various loads (19.60–58.86 N) and sliding distances (1200–2400 m) on pin-on-disk test rig was investigated for commercial purpose of machine components. Three sets of composites were fabricated with 4–12 % of silicon nitride by stir casting technique. SEM Micrographs revealed formation of a homogeneous α-aluminum dendrites network structure developed due to the super-cooling of casting during solidification. EDS showed increased content of hard silicon and nitrogen from 29.04 to 73.96 % and 6.68–14.54 % respectively with 4–12 % reinforcement addition which led to high hardness. Increase in hardness from 58.02 to 63.70 BHN is observed with increase in reinforcement which led to reduction in wear by reducing the actual contact area during sliding whereas strength is reduced on addition of Si3N4. The wear resistance of composite is found greater with 12 % Si3N4 reinforced composite with reduced wear at low sliding distance. Due to continuous sliding, wear debris embedded with the surface forming a layer which resulted in variation in coefficient of friction (COF). COF increased at a high rate up to 1800 m followed at a slow rate up to 2400 m sliding distance with increase of normal load. SEM analysis of worn surfaces revealed removal of surface layer with generation of micro cracks with subsequent sliding in composites reinforced with 4 % and 8 % silicon nitride whereas ploughing mechanism is observed in composite with addition of 12 % Si3N4. The linear increasing trend was observed in wear loss against the dissipated energy for the investigated composites.