Improving hardness of biomedical Co–Cr by deposition of dense and uniform TiN films using negative substrate bias during reactive sputtering

This paper reports the deposition of a fully dense and uniform TiN film to improve the surface hardness of Co–Cr, particularly, by applying a negative substrate bias during reactive direct current (DC) sputtering. As the TiN film was deposited with a negative substrate bias voltage of 150 V, the microstructure of the films was shifted from a columnar to non-columnar one that was observed to have a dense, uniform and smooth surface. In addition, the preferred orientation was the (111) plane when the films were deposited with a negative substrate bias; however, the (200) plane when they were deposited without a substrate bias. The deposition of the dense and uniform TiN film resulted in a significant increase of the hardness of the Co–Cr. The TiN-deposited Co–Cr with a negative substrate bias showed a very high hardness of 44.7 ± 1.7 GPa, which was much higher than those of the bare Co–Cr (4.2 ± 0.3 GPa) and TiN-deposited Co–Cr without a negative substrate bias (23.6 ± 2.8 GPa).