Plasma sprayed carbon nanotube and graphene nanoplatelets reinforced alumina hybrid composite coating with outstanding toughness

Abstract

Carbon nanotube (1 wt. %) and graphene nanoplatelets (0.5 wt. %) reinforced aluminum oxide (Al2O3) coating have been deposited on low carbon steel substrate using atmospheric plasma spray technique. Addition of 1 wt. % CNT and 0.5 wt. % GNP has significantly increased the densification from 88% in Al2O3 coating to 97% of the theoretical density in Al2O3 - 1 wt.% CNT- 0.5 wt.% GNP. Relative hardness and elastic modulus has increased by 52% and 48% respectively on synergistic addition of CNT and GNP. Increase in hardness was attributed to improved densification, while increased elastic modulus was due to higher elastic modulus of CNT and GNP and homogeneous distribution of CNT in Al2O3 matrix. An exceptional improvement of 200% in relative fracture toughness was observed in Al2O3 - 1 wt.% CNT- 0.5 wt.% GNP coating. The improvement in fracture toughness is attributed to three major factors viz. (a) increased densification (b) Strong Al2O3, CNT and GNP interface and (c) various toughening mechanism offered by CNT and GNP such as such as bridging and pull out, crack deflection, GNP Splat gluing, nanomechanical interlock etc.