A comparison of mechanical and wear properties of plasma sprayed carbon nanotube reinforced aluminum composites at nano and macro scale

The macro- and nano-scale mechanical and wear properties of carbon nanotube (CNT) reinforced Al-Si composite coatings prepared by plasma spraying have been compared in this paper. The composite coatings show a two phase microstructure; one phase being the Al-Si matrix with well dispersed CNTs and the other being the CNT clusters. Nanoindentation testing on the matrix portion with dispersed CNTs indicated an increase in the elastic modulus by 19% and 39% and an increase in the yield strength by 17.5% and 27% by the addition of 5 wt.% and 10 wt.% CNTs respectively. Macro-scale compression tests indicated no improvement in the elastic modulus but an increases in the compressive yield strength by 27% and 77% respectively, by addition of 5 wt.% and 10 wt.% CNTs. Nanoscratch testing carried out on the Al-Si matrix with dispersed CNTs indicated a decrease in scratch volume by 34% and 71% by addition of 5 wt.% and 10 wt.% CNTs respectively. Macro-scale wear tests indicated a decrease in the wear volume by 68% in case of 5 wt.% CNT coatings but an increase in the wear volume by 15% for the 10 wt.% CNT coating. The differences in mechanical and wear properties at nano and macro scales are explained in terms of the bimodal CNT dispersion (well dispersed and clusters) in Al-Si matrix, CNT cluster size and fraction and carbide formation. (C) 2011 Elsevier B.V. All rights reserved.