A Study on Micro-hardness and Tribological Behaviour of Nano-WC-Co-Cr/Multi-walled Carbon Nanotubes Reinforced AZ91D Magnesium Matrix Surface Composites

摘要

In the present study, AZ91-D magnesium alloy based metal matrix surface composites (MMSCs) were fabricated by multi-pass friction stir processing (FSP) technique. The nano-WC-Co-Cr and multi-walled carbon nanotubes (MWCNTs) as reinforcements were added by multi-pass FSP using grooving method. The effect of different volume fractions (%) of nano-reinforcements on the micro-structure, micro-hardness and tribological properties of MMSCs were studied. The AZ91-D parent material showed poor micro-hardness and tribological performance which could be attributed to coarse grain microstructure and secondary beta-phase distributed on the grain boundaries. On the other hand, friction stir processed material and fabricated MMSCs exhibited improved micro-hardness and tribological properties. This improved performance could be attributed to the homogeneous dispersion of reinforcement particles, dynamically recrystallized ultra-fine structure, and the dissolution of secondary beta-phase. Among the different nano-MMSCs reinforced with pure MWCNTs, pure WC-Co-Cr and its hybrid. The WC-Co-Cr/MWCNTs (1:1 ratio) hybrid composite exhibited a maximum average micro-hardness of 118.05 HV, minimum wear rate of 0.45 x 10(-3) mm(3)/m. But the minimum coefficient of friction (COF) of 0.32 was obtained in case of pure MWCNTs reinforced MMSC. Wear mechanisms like micro-cutting, micro-ploughing, delamination etc. were also evident from the SEM images.