Synthesis of aluminum oxide coating with carbon nanotube reinforcement produced by chemical vapor deposition for improved fracture and wear resistance

Chemical vapor deposition (CVD) was used to achieve a homogeneous dispersion of carbon nanotubes (CNTs) on aluminum oxide (Al2O3) powder. This powder was plasma sprayed onto a steel substrate to produce a 96% dense Al2O3 coating with CNT reinforcement. Addition of 1.5 wt.% CNTs showed a 24% increase in the relative fracture toughness of the composite coating. The improvement in the fracture toughness is attributed to uniform dispersion of CNTs and toughening mechanism such as CNT bridging, crack deflection and strong interaction between CNT/Al2O3 interfaces. Wear and friction behavior of the CNT reinforced Al2O3 coating under dry sliding condition was investigated by ball-on-disk tribometer. With the increasing normal loads from 10 to 50 N, the wear volume loss and coefficient of friction of the coating increased, owing to transition from the mild to severe wear. Wear resistance of the Al2O3–CNT composite coating improved by ∼27% at 50 N. Coefficient of friction at 50 N was dependent on the competing phenomena of wear debris generation and graphitization due to pressure.