Vanessa Vidal

Mechanical and Thermo-physical Properties of Plasma-Sprayed Thermal Barrier Coatings: A Literature Survey

Atmospheric plasma-sprayed thermal barrier coatings (APS TBCs) have been studied from an extensive review of the dedicated literature. A large number of data have been collected and compared, versus deposition parameters and/or measurement methods, and a comparison was made between two different microstructures: standard APS coatings and segmented coatings. Discussion is focused on the large scattering of results reported in the literature even for a given fabrication procedure. This scattering strongly depends on the methods of measurement as expected, but also—for a given method—on the specific conditions implemented for the considered experimental investigation. Despite the important scattering, general trends for the correlation of properties to microstructure and process parameters can be derived. The failure modes of TBC systems were approached through the evolution of cracking and spalling at various life fractions.

Mechanical Behavior of Ti-6Al-2Sn-4Zr-2Mo Titanium Alloy under Hot and Superplastic Forming Conditions: Experiment and Modeling

Titanium alloys are widely used in the aircraft industry. Under sheets form, they can be employed to the manufacturing of pylon or engine parts. With the aim of a cost reduction, this study proposes to act on the starting microstructure so as to improve the mechanical properties during the forming stages. In the present study, investigations are focused on Ti-6Al-2Sn-4Zr-2Mo (Ti6242) alloy specially used for the hot areas (e.g. parts close to the engine or the combustion chambe...). Presently, an important mechanical test campaign was performed on Ti6242 alloy, it examines, on the one hand, the microstructure qualified by the aircraft industry and, on the other hand, a new range of refined microstructures obtained by hot straining process. For each test, microstructural observations exhibited complex phenomena including simultaneously both grain growth and dynamic recrystallization. The occurrence, sequencing and coupling of the mechanisms, strongly depend on the starting microstructure and the test conditions (time-temperature and strain rate) investigated. They are not easy to understand and require further tests and observations. In such a framework, the implementation of mechanical models are efficient and relevant to promote a better knowledge of the microstructural evolution observed and their influence on the mechanical behavior.

Hot Forming Process Analysis of Ti6Al-4V Alloy: Experiment, Behaviour Modelling and Finite Element Simulation

The present investigation aims at evaluating and understanding the thermo-mechanical be-haviour of a titanium alloy under hot forming conditions. In this work, several considerations are ad-dressed. First, Scanning Electron Microscopy observations are performed to assess the evolutions of(α − β) phases, grain size, defects regarding the thermo-mechanical loadings from different static anddynamic tests (various temperatures and strain rates). Hence, the relationships between mechanicalproperties and micro-structure evolutions in such conditions allow a first assessment of the deforma-tion mechanisms in link with the macroscopic stress-strain curves. Afterwards, a behaviour modelformulation associated to an identification procedure of the parameters of the constitutive equationsis proposed. Finally, several tests performed under hot forming conditions and conducted on an in-dustrial press are compared to Finite Element calculations. Results are compared and provide someinteresting improvement ways in order to investigate the influence of the process parameters on thefinal shape of the part.