Yttria-stabilized zirconia films grown by radiofrequency magnetron sputtering: structure, properties and residual stresses

Thin (<10 mm) zirconium oxide films were deposited onto aluminium substrates by radiofrequency (RF) magnetron sputtering at different processing conditions. Structure, composition, residual stresses and mechanical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and depth-sensing indentation. All the films evidenced a good adhesion to the substrate. Their composition was always a mixture of tetragonal and monoclinic ZrO2 phases in different amounts grown with a strong preferential crystallographic orientation along the axis perpendicular to the aluminium substrate. According to Raman spectroscopy characterizations, the monoclinic phase was shown to possess an inhomogeneous distribution along the film thickness. The films experienced compressive residual stresses of relatively high magnitude in the range 300-700 MPa with non-monotonous profiles along the film thickness. According to depth-sensing indentation techniques, the Young's modulus and the hardness of the films were also characterized and revealed in some cases a marked peak-load dependence.