MSA  Vol.3 No.4 , April 2012
Modulus and Hardness Change of Silicon and Sapphire Substrates by TiC/VC Multilayer Coatings
The nanohardness H of multilayer specimens TiC/VC@Si and TiC/VC@Sapphire prepared by Pulsed-Laser-Deposition is investigated to check the existence of a superlattice effect as known from TiN/VN multilayers. In the present work the multilayer period thickness λ varies between 1.34 nm and 24.8 nm (total layer thickness t ≈ 200 nm). Unlike Young’s modulus E, H is enhanced, regardless of t, by covering Si as well as sapphire with a TiC/VC multilayer; the relative load carrying capacity being larger for Si. The maximum value of H obtained is 38 GPa for TiC/VC@Sapphire. It is observed for a multilayer thickness of λ ≈ 10 nm. Hardness of TiC/VC@Sapphire obeys, after annealing, a Hall-Petch relation H = 35.25 + 6.945 λ–0.5 (H in GPa und λ≥ 10 nm). From orientation dependent X-ray absorption fine structure and X-ray reflection records, short-range order and layer geometry are derived. These analyses reveal a continuous approach of interatomic distances Ti-C and V-C for deceasing multilayer periods. High-resolution transmission electron microscopy shows that multilayers are nanostructured, i.e., not only TiC/VC phase boundaries but also subgrains represent obstacles against plastic deformation. Dislocations play a major role as sources of internal stress and vehicles of plasticity.

Cite this paper
A. Belger, M. Reibold and P. Paufler, "Modulus and Hardness Change of Silicon and Sapphire Substrates by TiC/VC Multilayer Coatings," Materials Sciences and Applications, Vol. 3 No. 4, 2012, pp. 185-194. doi: 10.4236/msa.2012.34029.
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