Nanostructured Ceramic Coatings Produced by Magnetron Sputtering

Abstract

Zirconia based coatings, because of optical properties (high refractive index, low absorption over a broad spectral region from near-UV to mid-IR, high pulse laser damage threshold), thermal properties (low thermal conductivity and high thermal expansion coefficient), high dielectric constant, mechanical properties (high fracture toughness, thermal shock resistance) and corrosion-resistant properties at high temperatures, have many important scientific and technological applications. Physical Vapor Deposition (PVD) techniques, in particular magnetron sputtering are suitable technologies to deposit ceramic coatings with tailored structure (nanocomposite and multilayered coatings). Zirconia-Alumina (ZrO2-Al2O3) nanolayered thin coatings are a new method to stabilize the zirconia high temperature tetragonal phase at room temperature. ZrO2-Al2O3 transformation-toughening nanolaminates were prepared by reactive magnetron sputtering. in this contribution it is studied the structural properties of ZrO2-Al2O3 nanostructured coatings. The paper begins with a brief overview of nanolayer concepts and nanoscaled coating architecture, properties of zirconia ceramics and structural stability study of zirconia coatings. Coatings of pure (undoped) zirconia presents a monoclinic phase with traces of tetragonal. The nanostructured coatings present a ZrO2 polycrystalline phase (monoclinic and tetragonal phases depending on the ratio of thickness in the nanolaminated structure) and an A12O3 amorphous phase. The ZrO2 high temperature tetragonal phase content increases, as the nanolayers get thinner. After annealing in air at 1000°C the alumina is preserved in amorphous state and the quasiamorphous tetragonal zirconia nanosized grains crystallizes to tetragonal phase without any monoclinic transformation.