Structure and properties of Cr–B, Cr–B–N and multilayer Cr–B/Cr–B–N thin films prepared by r.f.-sputtering

Cr–B, Cr–B–N and Cr–B/Cr–B–N multilayer films were synthesized by r.f. plasma-assisted magnetron sputtering using a CrB target (99.9% in purity) on silicon wafer substrates. The multilayer coatings were prepared by sequential sputtering using a nitrogen gas flow controller and a shutter by the sputtering of the CrB target. The films were deposited with an r.f. power of 120 W (target) and 100 W (coil) without substrate bias application, and the film thickness was controlled to ∼1 μm by adjusting the sputtering time. The micro-structure of thin films was studied by XRD and TEM and the chemical bonding state of films was investigated by XPS. The hardness and Youngʹs modulus of the films were studied in detail by the nano-indentation system. A ball-on-disk tribometer was used to measure the friction and wear behavior. A study of their microstructure and mechanical properties has provided the following results: XRD, TEM and XPS measurements revealed that the Cr–B films consist of CrB phase mainly and Cr–B–N films contain CrB and h-BN phase with an amount of unknown phases. The hardness for the films of Cr–B and Cr–B–N was 17 and 13 GPa, respectively. On the other hand, Cr–B/Cr–B–N multilayer films exhibited higher hardness reaching to 20 GPa regardless of the sublayer thickness. Cr–B and Cr–B–N films showed the Youngʹs modulus of 204 and 216 GPa, respectively. The Youngʹs modulus of Cr–B/Cr–B–N multilayer films increased to approximately 240 GPa regardless of the sublayer thickness as well. Furthermore, the friction coefficient of Cr–B/Cr–B-N multilayer exhibited an intermediate value of ∼0.45 between those of Cr–B (0.9) and Cr–B–N (0.2).