Abstract
Films of CrN, $Cr_{40}Zr_9N$, and $Cr_{31}Zr_{16}N$ were deposited on a steel substrate by closed field unbalanced magnetron sputtering, and their oxidation behaviors at $700^{\circ}C$ and $800^{\circ}C$ for up to 60h in air were investigated. All the deposited films were composed of the CrN phase. Zirconium atoms in $Cr_{40}Zr_9N$ and $Cr_{31}Zr_{16}N$ films partially dissolved in the CrN phase. They advantageously refined the columnar structure, reduced the surface roughness, and increased the microhardness. The CrN film displayed relatively good oxidation resistance, owing to the formation of the highly protective $Cr_2O_3$ on its surface. The $Cr_{40}Zr_9N$ and $Cr_{31}Zr_{16}N$ films oxidized to $Cr_2O_3$ as the major phase and ${\alpha}-ZrO_2$ as the minor one. They oxidized primarily by the inward transport of oxygen. The addition of Zr could not increase the oxidation resistance of the CrN film, because the formed $ZrO_2$ that was intermixed in the $Cr_2O_3$-rich oxide layer was oxygen permeable, and developed the compressive stress in the oxide scale owing to the volume expansion during its formation.
