Mechanical properties evaluation of diamond films via nanoindentation

Diamond film is considered ideal tool coating material for processing difficult-to-machine materials due to the high hardness and wear resistance. However, precisely evaluating the mechanical properties of diamond films has been a considerable obstacle, which hinders further design and application. In this work, various diamond films were deposited on cemented carbide substrates ranging from 0.1 to 1.0 kPa in CH4/H2 by hot filament chemical vapor deposition. The mechanical properties of diamond films were systematically and rigorously evaluated by nanoindentation adopting a series of loads. However, it is found that hardness calculated at different loads has a significant deviation, although all obey the well-known 10 % rule of thumb. On basis of the massive nanoindentation on polished diamond film with roughness <20 nm, we propose a stricter 5 %, instead of the well-known 10 % rule of thumb, for the limit of maximum penetration depth divided by film thickness in the diamond nanoindentation measurements. Notably, the mechanical properties of the deposited diamond films improved as the pressure increased, especially hardness gradually increased from 75.5 +/- 1.4 GPa to 87.3 +/- 5.0 GPa, which is attributed to the increase of the ratio of sp3 carbon content.

Automated summary

Diamond film is an ideal coating material for difficult-to-machine materials due to its high hardness and wear resistance. However, accurately evaluating the mechanical properties of diamond films has been a challenge. This study evaluates the mechanical properties of diamond films using nanoindentation and proposes a stricter evaluation standard.