A functionally graded design study for boron carbide and boron carbonitride thin films deposited by plasma-enhanced DC magnetron sputtering

The B-C-N system is characterized by short bond lengths and includes the hardest known materials, c-BN and B4C, as well as other materials with remarkable tribological properties such as h-BN. Despite these good properties, adhesion problems were observed for B4C and BCN thin films on steel and Si substrates when the film thickness exceeds 500 nm. To enhance the adhesion, three functionally graded designs; surface boronizing of the steel substrate before deposition (Boride underlayer/B4C), Ti/TiC/B4C and Ti/TiN/BCN structures were discussed. Cross-sectional FE-SEM examinations and elemental depth profiling by SIMS were revealed the graded structure of the films. The elemental film composition was measured by EPMA. The mechanical properties were determined by nanoindentation and the tribological properties by pin-on disc measurements. The results demonstrated the possibility of growing well adherent boron carbide and boron carbonitride films with thicknesses in the mu m range.