Mechanical properties of single and multilayer CrN films synthesized by pulsed DC sputtering

Abstract

Chromium nitride (CrN) films were synthesised by reactive pulsed DC sputtering (PMS) of a chromium target in the presence of argon (Ar) and nitrogen (N2) gas mixture operated at 20 kHz and 30% duty cycle. Experiments were conducted to study the effect of target voltage on the structure and mechanical properties of the films. Deposited films were analysed for their structure, hardness and adhesion using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), nanoindentation and nanoscratch. Transition from cubic phase CrN (c-CrN) to hexagonal phase Cr2N (β-Cr2N) was observed with increase in target voltage. A single layer 430 nm thick film deposited at 450 V showed good mechanical properties with hardness of 19.5 GPa and critical load of 18 mN. Further, inter-and multi-layer Cr/CrN films showed the presence of c-CrN phase with a strong (200) reflection along with weak c-CrN (111) and β-Cr2N (110) reflections. Cr interlayered CrN film deposited at a target voltage of 450 V showed a hardness of 19.7 GPa and critical load of 27.7 mN. As compared to a single layer CrN, for a 8 bilayered Cr/CrN film of 1μm thickness, the hardness remained the same (18.2 GPa) while the adhesion of the film improved greatly from a critical load of 18 mN to 86 mN.