Tribological behaviour of eggshell ash and boron carbide reinforced ZA-27 hybrid metal matrix composites under dry sliding conditions

The present investigation intends to study the tribological behaviour of ZA-27 alloy reinforced with low-cost eggshell ash (ESA) and boron carbide (B4C) particles by utilizing a stir casting process to fabricate hybrid metal matrix composites. The percentage of ESA and B4C particles are added in the range of 0-5 wt.%. Composites being tested for density, porosity and microhardness. A pin-on-disc DUCOM tribometer used to investigate the friction and wear behaviour of composites with a varying load of 10 to 50 N at a constant sliding speed of 1 m s(-1) and a fixed sliding distance of 1500 meter. To study the influence of speed on friction and wear behaviour, tribological testing was also performed at a sliding speed of 2 m s(-1) and 3 m s(-1). The composites microstructure revealed the presence of ESA and B4C particles examined by scanning electron microscope (SEM) and energy-dispersive x-ray spectroscopy (EDS) analysis confirmed the elemental composition of reinforcement particles present in the matrix. Composites density decreased when reinforced with ESA and B4C particles and the maximum decrease in density was about 3.12%. Porosity of the composites increased with the increase in wt.% of B4C particles. Addition of ESA and B4C particles significantly improved composites microhardness. The coefficient of friction (COF) and wear loss showed an increasing trend with the increase in load, whereas COF decreased and wear loss increased on higher sliding speeds. Composites showed superior wear resistance over base alloy under all test conditions. Worn surface morphology indicated the delamination, plastic deformation and ploughing at low speed, whereas abrasion was the dominant wear mechanism at higher sliding speeds. Therefore, this hybrid composite may have the potential to be used as a bearing material for tribological applications over monolithic ZA-27 alloy.