<p>Coatings are frequently applied on gas turbine components inorder to restrict surface degradation such as corrosion andoxidation of the structural material or to thermally insulatethe structural material against the hot environment, therebyincreasing the efficiency of the turbine. However, in order toobtain accurate lifetime expectancies and performance of thecoatings system it is necessary to have a reliableunderstanding of the mechanical properties and failuremechanisms of the coatings.</p><p>In this thesis, mechanical and fracture behaviour have beenstudied for a NiAl coating applied by a pack cementationprocess, an air-plasma sprayed NiCoCrAlY bondcoat, a vacuumplasma-sprayed NiCrAlY bondcoat and an air plasma-sprayed ZrO₂+ 6-8 % Y₂O₃topcoat. The mechanical tests were carried out ata temperature interval between room temperature and 860oC.Small punch tests and spherical indentation were the testmethods applied for this purpose, in which existing bending andindentation theory were adopted for interpretation of the testresults. Efforts were made to validate the test methods toensure their relevance for coating property measurements. Itwas found that the combination of these two methods givescapability to predict the temperature dependence of severalrelevant mechanical properties of gas turbine coatings, forexample the hardness, elastic modulus, yield strength, fracturestrength, flow stress-strain behaviour and ductility.Furthermore, the plasma-sprayed coatings were tested in bothas-coated and heat-treated condition, which revealedsignificant difference in properties. Microstructuralexamination of the bondcoats showed that oxidation with loss ofaluminium plays an important role in the coating degradationand for the property changes in the coatings.</p><p><b>Keywords:</b>small punch test, miniaturised disc bendingtests, spherical indentation, coatings, NiAl, APS-NiCoCrAlY,VPS-NiCrAlY, mechanical properties</p>

La texture marquée des tôles et des gaines en alliages de zirconium se traduit par une forte anisotropie du comportement mécanique. L'objectif de l'étude est de caractériser et de modéliser le comportement anisotrope de tôles en alliage de Zircaloy-4 recristallisé. La caractérisation de l'anisotropie du comportement est réalisée au travers d'essais mécaniques conventionnels (chargements en traction et en cisaillement) sur tôles en utilisant la méthode de corrélation d'images numériques. Dans un premier temps, un modèle a été identifié à partir de cette base expérimentale sur tôle. La loi est validée par des calculs éléments finis d'essais de traction sur éprouvettes plates entaillées. Dans un second temps, la transférabilité du modèle de la tôle vers le tube a été étudiée. Pour les chargements uniaxiés, la transférabilité est avérée. En revanche, pour les chargements biaxiés la transférabilité est moins bonne. Une réidentification des paramètres gérant l'anisotropie du comportement en intégrant à la base d'identification un essai équibiaxié sur tube a été nécessaire. / Zirconium alloy sheet and clad are strongly textured materials, resulting in sharp anisotropic mecanical behavior. The purpose of this work is to characterize and model the anisotropic behavior of recrystallized Zircaloy-alloy sheets. Anisotropy is investigated by usual mechanical tests (tensile and shear loadings) performed on sheet material using digital image correlation measurments. A model is identified from this experimental database obtained on sheet material. Finite element simulations of tensile notched tests are used to validate the law. Then, the model transferability from the sheet to the rod is studied. The transferability is suitable for uniaxial loading. On the contrary, the transferability is not fully adequate for biaxial loadings. Therefore, a new identification of parameters dealing with anisotropy from enriched database with an equibiaxial rod test is necessary.

The issue of ductile damage prediction can be generally divided in two types of tasks. The first one is to preventing the initiation of ductile damage with is most common group of calculation today. The second task can be described as aimed damaging, such as machining, cutting, etc. The significant development of this issue occurred in recent decades by help of development and access to powerful computational techniques and new experimental possibilities. However, the behaviour of ductile damage at multiaxial proportional and non-proportional loading is insufficiently described. This thesis helped to clarify some of the unknown this topic. It contributed to the understanding of selected materials behaviour at room temperature and quasistatic loading. Austenitic stainless steel AISI 316L was selected for detail study of ductile damage. A large number of experiments were performed on this material, such as uniaxial tensile tests of smooth and notched specimens, upsetting tests of smooth cylinder and special cylinder with dimple, butterfly specimens, notched tube specimens and penetration tests. Experimental results is used for calibration of five so-called simple criteria, taking into account fracture strain and stress triaxiality (Equivalent fracture strain, Johnson-Cook, simplify Bao-Wierzbicki, RT, RTCL) and universal criteria (Bai-Wierzbicki, Xue-Wierzbicki, EMC, LOU, KHPS). SPT potentially enable the determination of actual mechanical behaviour using only a fraction of specimen volume compared to standard specimen. It is promising tool to improve accuracy when assessing working life of components in operation. The inverse numerical simulation loop of SPT was designed using program OptiSLang on the basis of detailed sensitivity analysis. It was achieved 2% deviation of yield strength and 6% deviation of ultimate strength obtained from tensile tests. A several modification of SPT specimen was suggested for universal criteria calibration of small material volume. The 3D numerical model was built for numerical simulation with ductile damage simulation. The criteria KHPS and EMC gave the most accurate results.

The presented diploma thesis deals with an innovative material test, so called Small Punch Test. There are main principles, advantages and limitations of the test stated in the thesis. There are stated also correlation procedures in order to obtain standard mechanical properties. A test fixture design has been done in order to perform test procedures at temperature range from 80 to 25 °C. Twelve experimental curves have been obtained from the test and typical quantities have been evaluated. The different accuracy of correlations with standard mechanical properties has been obtained using different correlation equations.

Diploma thesis is focused on mechanical properties testing by small punch test and comparison of these properties with mechanical properties obtained by conventional tensile test. Steels P92 and AISI 316L in a shape of discs were tested. There were determined values of mechanical properties, namely yield stress, and ultimate tensile stress, obtained by the small punch test – constant deflection rate in this thesis. Values of initial stress and residual stress were evaluated from relaxation small punch test. Mechanical properties obtained by small punch test – constant deflection rate, and small punch test – relaxation, respectively, are compared with mechanical properties obtained by conventional tensile test, and relaxation tensile test, respectively. There were proposed own empirical relationships for restatement of mechanical properties obtained by small punch test to mechanical properties obtained by conventional tensile test in the thesis. Relatively small agreement of results obtained by small punch test, and conventional tensile test was demonstrated by a comparison. Application of own empirical relationships resulted in better agreement. Very good agreement of results of small punch test – relaxation, and relaxation tensile test was shown by their comparison.

The aim of diploma thesis is estimate mechanical properties (yield strength, maximum strength and elongation) of light alloys by means of SPT. For the experiments were selected aluminium alloys (Al 2024, Al 6082 T6, Al 7020 and NASA 398) magnesium alloys (MgZnMn, AZ31, AZ61) and composites (AZ91 + 20 % saffilu a Al + Al4C3). Theoretical part of this thesis is focused on analysis of conversion formulas, which were made from SPT data and conventional testing. Experimental part is dedicated to evaluation of experimental data and critical analysis validity of conversion formulas. In this part of thesis is discused the problematics of reproducibility methodology of SPT.