Post-annealing effect on the structural and mechanical properties of multiphase zirconia films deposited by a plasma focus device

Abstract

Nanostructured multiphase zirconia films (MZFs) are deposited on Zr substrate by the irradiation of energetic oxygen ions emanated from a plasma focus device. The oxygen operating gas pressure of 1 mbar (1 bar = 105 Pa) provides the most appropriate ion energy flux to deposit crystalline ZrO2 films. X-ray diffraction (XRD) patterns reveal the formation of polycrystalline ZrO2 films. The crystallite size (CS), crystal growth, and dislocation densities are attributed to increasing focus shots, sample axial distances, and working gas pressures. Phase and orientation transformations from t-ZrO2 to m-ZrO2 and c-ZrO2 are associated with increasing focus shots and continuous annealing. For lower (200 °C) annealing temperature (AT), full width at half maximum (FWHM) of diffraction peak, CS, and dislocation density (δ) for (020) plane are found to be 0.494, 16.6 nm, and 3.63 × 10−3 nm−2 while for higher (400 °C) AT, these parameters for (111) plane are found to be 0.388, 20.87 nm, and 2.29 × 10−3 nm−2, respectively. Scanning electron microscope (SEM) results demonstrate the formation of rounded grains with uniform distribution. The estimated values of atomic ratio (O/Zr) in ZrO2 films deposited for different axial distances (6 cm, 9 cm, and 12 cm) are found to be 2.1, 2.2, and 2.3, respectively. Fourier transform infrared (FTIR) analysis reveals that the bands appearing at 441 cm−1 and 480 cm−1 belong to m-ZrO2 and t-ZrO2 phases, respectively. Maximum microhardness (8.65±0.45 GPa) of ZrO2 film is ∼ 6.7 times higher than the microhardness of virgin Zr.