Alumina-Zirconia composites : elaboration and characterization in view of the orthopaedic application : elaboration and characterization in view of the orthopaedic application

par Valentina Naglieri

Thèse de doctorat en Matériaux

Sous la direction de Jérôme Chevalier et de Laura Montanaro.

Soutenue en 2010

à Lyon, INSA en cotutelle avec Politecnico di Torino .


  • Résumé

    The aim of this thesis is the elaboration of the alumina – zirconia composites, for orthopaedic application (femoral heads), through a colloidal method, which allows tailoring the size and distribution of zirconia grains. A first part of this work deals with the elaboration of the composite powder, obtained by surface modification of a commercial, submicrometer alumina powder. These powders were characterized in terms of phase evolution, thermal behaviour, kinetics and mechanism of the zirconia crystallization. The evolution and the kinetics of the zirconia crystallization were studied by conventional and high temperature X-Rays Diffraction. The crystallization mechanism was studied in detail, coupling the results of the kinetics investigations and the observations by Transmission Electron Microscope (TEM and HRTEM) of the powders treated at different temperatures. This study allowed the optimization of the thermal treatment, in order to preserve the homogeneity and the desired characteristics in the final microstructure. Composite powders, containing different zirconia amounts (between 5 and 20 vol. %), were prepared by this procedure. Some samples obtained by slip casting of the dispersed suspension were sintered and used for a preliminary characterization. Indentation tests were performed on the different samples, in order to evaluate the Vickers Hardness and the threshold for slow crack propagation, KI0. The composite containing 10 vol. % ZrO2 exhibited the maximum KI0. The toughening is due to the t ®m transformation induced at the crack tip. The last part of this thesis deals with the elaboration of the femoral heads prototypes, by following a procedure compatible with the industrial strategy. The prototypes were obtained by isostatically pressing the spray dried powder. The green density was about 58. 2 % of the theoretical density (TD). After natural sintering, the mean density was 99. 3 % TD. Finally, after hot isostatic pressing, the density was close to the theoretical one. Hardness measurements were performed to evaluate the homogeneity of this property inside the ceramic spherical bodies. The hardness values obtained near the external surface and in the centre are comparable (~1956. HV), demonstrating that the density and the mechanical properties are constant inside the ceramic sphere, independently from the position. Moreover, the threshold for slow crack propagation, KI0, was determined by Vickers indentation carried out along a diameter of a sample cross section. The mean KI0 is 3. 8 ±0. 3 MPa·m1/2. This value was comparable to that obtained for slip cast samples containing the same zirconia amount (3. 5 ±0. 3 MPa·m1/2), demonstrating that the good results obtained by slip casting, for small pellets, can be reproduced by cold isostatic pressing of atomized powder, in larger spherical components

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Informations

  • Détails : 1 vol. (IX-151 p.)
  • Annexes : Références en fin de chapitres

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