Dependence of structure and properties of hard nanocrystalline conductive films MBCN (M = Ti, Zr, Hf) on the choice of metal element

• MBCN (M = Ti, Zr, Hf) films were prepared by reactive magnetron sputtering.
• Amorphous (M = Ti) and 2 different nanocomposite (M = Zr, Hf) structures were observed.
• Explanation (supported by ab-initio calculations) was found.
• At a low N content the Ti → Zr → Hf transition improves mechanical properties.
• At a medium N content the Ti → Zr → Hf transition increases electrical resistivity.

The paper deals with hard nanocrystalline conductive films MBCN (M = Ti, Zr, Hf) prepared by pulsed dc reactive magnetron sputtering. We focus on the effect of the choice of metal element (at fixed contents of the non-metal elements and fixed deposition parameters) on material structure and properties. We find that the transition from Ti through Zr to Hf leads to an increasing preference to form stable MBxCyN1 − x − y solid solutions, and (consequently) to more pronounced crystallinity and texture. These results are compared with and explained by ab-initio calculations. At a low N content the transition from X-ray amorphous TiBCN to truly nanocrystalline or even nanocomposite ZrBCN and HfBCN leads to increased hardness (from 21 to 33–37 GPa), increased hardness to effective Young's modulus ratio (from 0.098 to 0.132–0.133) and increased elastic recovery (from 67 to 82–85%). At a medium N content the transition from TiBCN (which is homogenous) to ZrBCN and HfBCN (where small conductive nanocrystals are separated by an insulating amorphous phase) dramatically increases the electrical resistivity (from the order of 10− 6 to the order of 103–106 Ωm). The results are important for the design of future hard and electrically conductive protective coatings with a high thermal stability.