Abstract

PORTINHA, A. et al. Propriedades mecânicas de revestimentos nanolaminados e nanoestructurados de ZrO₂/Al₂O₃ para aplicações de desgaste a alta temperatura. C.Tecn. Mat. [online]. 2006, vol.18, n.1-2, pp.57-64. ISSN 0870-8312.

Zirconia (ZrO₂) is a material with increasing interest for technological and scientific applications, due to its combination of properties. When total or partially stabilized it can be used as bulk material or as protective coatings at high temperature, even above 1000ºC. In particular, the coatings that we present in this work reveal promising for many technological applications where the chemical stability combined with wear resistance and high hardness are important for high temperature applications. The aim of this work is to present and to discuss the mechanical properties (such as hardness, modulus of elasticity, residual stresses and adhesion) of nanolayered and nanoestructured ZrO₂/Al₂O₃ coatings deposited by reactive Physical Vapour Deposition (PVD). The stabilized zirconia presents some advantages towards alumina possessing higher mechanical resistance combined with higher resistance to fracture. Moreover, when produced in a nanolayered structure have similar hardness and in some cases superior than alumina. This work presents two kind of coatings: ZrO₂/Al₂O ₃ coatings with a nanolayered structure that have been grown with different thickness of each nanolayer (3/3.5, 6/7 and 12/14 nanometers for each layer of ZrO2/Al₂O₃ respectively) and ZrO₂Al₂O₃ nanoestructured coatings where the percentage (wt%) of Al₂O₃ was changed between 1,7 and 9,1 wt% in order to stabilize the high temperature tetragonal phase of the zirconia at room temperature. The hardness and modulus of elasticity had been determined by nanoindentation tests using a Berkovich indenter for loads between 5 mN and 120 mN. At the lowest loads measurements reveals only the coatings properties where as at high loads the influence of both, coatings plastic behaviour and the substrate influence in mechanical properties are observed. For the nanolayered coatings and after heat treatment the hardness increases until 24 GPa, for the coatings grown with 12/14 nanometers of thickness for each nanolayer. Residual stresses have been determined using the Stoney equation and using Raman Spectroscopy measurements. All coatings present an increase of the residual stresses in compression after heat treatment. The adhesion of the nanolayered coatings was also evaluated by scratch-test measurements.

Keywords : zirconia; mechanical properties; nanolayered coatings; hardness; nanoindentation; scratch test; adhesion; PVD; ZrO₂/Al₂O ₃.

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