Identification And Growth Of Oxide Films On Zirconium In High Temperature Water

Author : Lukasz Kurpaska
Publisher :
ISBN 13 :
Total Pages : 215 pages
Book Rating : 4.:/5 (863 download)

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Download or read book Analyse Des Contraintes Mécaniques À Haute Température Dans Les Films D'oxyde written by Lukasz Kurpaska and published by . This book was released on 2012 with total page 215 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis work consist in developing the tools and the methods which are necessary to identify the thermo-mechanical behavior of oxide films growing on the surface of metallic materials by oxidation at high temperature. Special attention was provided specifically to identify the behavior of the oxide scale in the area most complex, located near the metal/oxide interface. For this purpose, we include : 1. Calculated deformations growth. 2. Characterized the evolution of the crystallographic structure of the oxide layer according to the parameters of oxidation. 3. Estimated the evolution of residual stresses using two complementary experimental techniques. The Zr=ZrO2 system has been chosen as support of this work. The first stage of the thesis is devoted to the determination of the exact role and contribution of epitaxial strain induced by the lattice mismatch between two crystallographic networks : metal and its oxide on the stress level. These deformations, specifically located near the metal/oxide interface, are difficult to assess and their calculation remains debatable. A generalization of the Bollmann's method, based on the formalism of the "O" - lattice has been implemented to evaluate these deformations. In order to validate it, a numerical approach has been developed and applied to the reference system, Ni=NiO. Application to the more complex system Zr=ZrO2 is then presented. Special attention has been given to study the sensitivity of the input parameters of the model, which is often poorly understood. The second part of this thesis is devoted to the determination of the stresses in the films of zirconia. To achieve this goal, the Raman spectroscopy technique has been used. By comparing the intensities and positions of characteristic peaks, the presence of a strong compressive stress in the oxide layer and in the region near the metal/oxide interface was shown. In parallel, in situ uniaxial tensile & compression loads were applied to the oxidized samples to correlate the stress level and the structural evolution in the oxide layer : this original study showed the influence of stress level on the proportion of the present phases. A transition from tetragonal to monoclinic phase has been identified and quantified. The technique of Raman spectroscopy has allowed us to highlight the influence of the thermal deformation on the stress level in the oxide layer during cooling process. The third part of this work deals with the determination of the stress level during the course of the oxidation process in zirconia films using the defection test method based on a thin oxidized on one side specimen concept, (DTMO - defection test in monofacial oxidation). In the course of this experiment, attached acoustic emission equipment is installed for in situ detecting and evaluating possible damages of the zirconia layer throughout the bending phenomenon (influence of temperature and oxidizing atmosphere). Modeling and simulation of these tests were used to estimate the interfacial stress level created in different temperatures in the zirconia film as a function of oxidation time. The comparison of the results of bending tests (comprehensive measures) and those obtained using the technique of Raman spectroscopy (local measurements) helped us to better understand the space and time evolution of stress within the thermo-mechanics zirconium oxide. The generalization of the Bollmann's method has contributed significantly to the understanding of the origin and quantification of constraints arising from lattice mismatch between the two metal oxide structures. Taken together, these results should significantly contribute to help the scientific community to better understand the origin and nature of constraints in zirconia films during their life cycle.