Carbon nanotubes improve the adhesion strength of a ceramic splat to the steel substrate

A scratch technique was used to measure the adhesion strength of plasma sprayed carbon nanotube (CNT) reinforced aluminum oxide (Al2O3) splat on the steel substrate. The effect of adding carbon nanotube on the adhesion strength of a single splat was studied by varying the CNT content as 0, 4 and 8 wt.% in the Al2O3 matrix. Higher lateral force was required by the nanoindenter tip to detach CNT reinforced Al2O3 splats as compared to Al2O3 splat. The adhesion strength increased significantly from 0.52 ± 0.05 MPa for Al2O3 splat to 4.21 ± 0.49 MPa for Al2O3-4 wt.% CNT splat and 7.36 ± 3.96 MPa for Al2O3-8 wt.% CNT splat. A high variation in the adhesion strength of Al2O3-8 wt.% CNT splat was due to varying degree of CNT dispersion in the matrix. A significant increase in the adhesion strength of Al2O3-CNT splat was attributed to its better mechanical interlocking with the substrate as a result of enhanced melting and spreading caused by the higher thermal conductivity of nanotubes. CNTs also form anchors between the splat and the substrate resulting in higher adhesion strength.