Abstract:A comparative study on the surface properties of Al-SiC-multi walled carbon nanotubes (CNT) and Al-SiC-graphene nanoplatelets (GNP) hybrid composites fabricated via friction stir processing (FSP) was documented. Microstructural characterization reveals a more homogeneous dispersion of GNPs in the Al matrix as compared to CNTs. Dislocation blockade by SiC and GNP particles along with the defect-free interface between the matrix and reinforcements is also observed. Nanoindentation study reveals a remarkable ~207% and ~27% increment in surface nano-hardness of Al-SiC-GNP and Al-SiC-CNT hybrid composite compared to as-received Al6061 alloy, respectively. On the other hand, the microhardness values of Al-SiC-GNP and Al-SiC-CNT are increased by ~36% and ~17% relative to as-received Al6061 alloy, respectively. Tribological assessment reveals ~56% decrease in the specific wear rate of Al-SiC-GNP hybrid composite, whereas it is increased by ~122% in Al-SiC-CNT composite. The higher strength of Al-SiC-GNP composite is attributed to the mechanical exfoliation of GNPs to few layered graphene (FLG) in the presence of SiC. Also, various mechanisms such as thermal mismatch, grain refinement, and Orowan looping contribute significantly towards the strengthening of composites. Moreover, the formation of tribolayer by the squeezed-out GNP on the surface is responsible for the improved tribological performance of the composites. Raman spectroscopy and various other characterization methods corroborate the results.

Key words: friction stir processing; graphene; carbon nanotube; hybrid composite; wear