Mechanical properties of superhard materials synthesised at various pressure–temperature conditions investigated by nanoindentation

Abstract

Nanoindentation is applied to synthetic diamond crystals, a chemical vapour deposition (CVD) grown diamond film and to aggregated diamond nanorods produced by high-pressure compression of fullerite. Characteristic load–displacement curves are used to determine the mechanical properties and to classify these materials. Atomistic simulations have also been carried out. The results show that diamond undergoes a mainly elastic deformation during nanoindentation. Both simulations and experiments show that the force exerted on the indenter varies as the depth raised to the power 1.6. Results for the CVD grown diamond films give smaller hardness values than for the diamond crystals. For the diamond nanorods sample, hardness values lie up to those determined for diamond, whereas the elastic modulus can exceed the diamond value.

Keywords:

• Nanoindentation
• Elastic modulus
• Superhard materials
• Computer simulation

Acknowledgements

We thank Dr Bodo Wolf, University of Applied Sciences Lausitz, Germany, for helpful discussions and permanent interest in this work and Mr Ronald Ries, Wildau, for practical support during the measurements. Dr Steven Kenny is also thanked for the help in programming the parallel algorithms in the MD code. This work has been performed partly through a joint project grant 2005/R1-JP of the Royal Society. Asta Richter and Roger Smith gratefully acknowledge financial support from the European Science Foundation for the attendance of the Workshop Novel Superhard Materials.