Thermal, electrical, and mechanical properties of hard nitrogen-alloyed Cr thin films deposited by magnetron sputtering

Abstract

CrN based materials, including stoichiometric CrN and Cr:N with a wide range of nitrogen contents, are commonly used as hard and corrosion-resistant coatings. Cr-rich films in this materials system can retain the bcc structure of metallic Cr with few percent of dissolved nitrogen, which can be used for tailoring the mechanical, thermal, and electrical properties. Here, we investigated low nitrogen containing Cr thin films deposited by high ion assisted magnetron sputtering with a substrate temperature of 200 °C. With the gas flow ratio maintained at fN2/Ar = 0.02, the substrate bias and the target power allows for control of the film composition (0.03 < N/Cr < 0.34). The films comprise a mixture of bcc-Cr and hexagonal Cr2N1-δ phases. The mechanical properties studied by nanoindentation and Brillouin inelastic light scattering revealed a hardening effect due to the multiphase nanostructure. The mechanical properties of the Cr:N films depend on the residual stress, on the amount of h- Cr2N1-δ phase and on the nanostructuring nature of the coatings. A maximum hardness of 37 GPa was achieved for a dense film with a Young's modulus of 340 GPa, a shear modulus of 118 GPa, and a relatively low thermal conductivity of 7 W/mK.