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[M/F] Micromechanical characterization at high temperature of Ti and Ni-based model materials after high temperature oxidation

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Date Limite Candidature : mardi 27 avril 2021

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General information

Reference : UMR5312-DAMTEX-005
Workplace : ALBI
Date of publication : Tuesday, April 06, 2021
Scientific Responsible name : Damien TEXIER and Marc LEGROS
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2021
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly

Description of the thesis topic

Structural metallic/intermetallic materials operating at high temperatures (650°C-1200°C) in severe environments are commonly subjected to in-service surface reactivity, i.e. oxidation, corrosion. This issue is encountered in several industrial applications, especially when high temperatures, mechanical stresses, and highly corrosive atmospheres gather (power plants, aeronautic turbines, etc.)[1]. Environment-assisted degradation alters both the surface of the materials and their bulk properties due to a progressive selective consumption of elements involved in the surface degradation process and/or diffusion of oxidising elements (e.g. depleted sub-surface layer for Ni-based superalloys due to Al consumption to form Al2O3 [2, 3], brittle oxygen/nitrogen-enriched layer in Ti and TiAl alloys due to O and N solubility [4, 5], etc.). The material in a shallow region beneath the reactive surface subsequently presents a gradient of chemistry, microstructure and physical properties. This gradient of microstructure and properties evolves with the time due to the oxide growth and diffusion processes.

Each family of metallic/intermetallic materials reacts differently to the so-called “stress-corrosion”, but also to the corrosive/oxidative-deformation. However, all the materials are potentially affected by these mechanisms due to the concomitant effects of surface reactivity, microstructure evolution and deformation. Despite the negligible scale of the physical, chemical, metallurgical gradients (from 0.1 to 100 micrometres beneath the surface) in comparison with the dimensions of the structural components, the variability in mechanical behaviour within the gradient often drives premature damage and the progressive rupture of the component [6]. Such material evolution and degradation could be included in the so-called “stress-corrosion cracking”, investigated for decades for all the structural materials used at high temperature. HOWEVER, industrial and ecological motivations to use structural materials in ever-more extreme, severe, harsh conditions push them to their performance limits. The synergy operating between inter- versus intragranular strain localisation and surface reactivity/diffusion processes promotes unexpected damage and high variability in lifespan of structural components exposed at “too high temperatures – too much (cyclic and/or steady) stresses” [7]. A better understanding of the thermo-mechano-chemical elementary mechanisms responsible of early damage at the microscale is needed.

Project motivations :

To address this point, HT-S4DefOx, a project funded by the European Research Council (ERC - Starting Grant), intends :
• To assess the mechanical behaviour within the time-evolving gradient of microstructure and properties, i.e. within the “sub-surface” material (micro- and mesoscale approach);
• To assess the variability in sub-grain mechanical behaviour of the metallic material at the metal/oxide interface (microscale approach). This interface, considered as the “extreme surface”; is on the front line for the thermo-mechano-chemical coupling;
• To model and simulate thermo-mechano-chemical coupling on time-evolving microstructures and properties of the “sub-surface” material with boundary conditions on the “extreme surface”.

References :
1. Young DJ (2016) High temperature oxidation and corrosion of metals, 2nd Ed. Elsevier Science
2. Bensch M, Preußner J, Hüttner R, et al (2010) Modelling and analysis of the oxidation influence on creep behaviour of thin-walled structures of the single-crystal nickel-base superalloy René N5 at 980 °C. Acta Mater 58:1607–1617. doi:10.1016/j.actamat.2009.11.004
3. Cassenti B, Staroselsky A (2009) The effect of thickness on the creep response of thin-wall single crystal components. Mater Sci Eng A 508:183–189. doi:10.1016/j.msea.2008.12.051
4. Finlay WL, Snyder JA (1950) Effects of three interstitial solutes (nitrogen, oxygen, and carbon) on the mechanical properties of high-purity, alpha titanium. JOM 2:277–286. doi:10.1007/BF03399001
5. Barkia B, Doquet V, Couzinié JP, et al (2015) In situ monitoring of the deformation mechanisms in titanium with different oxygen contents. Mater Sci Eng A 636:91–102. doi:10.1016/j.msea.2015.03.044
6. Pineau A, Antolovich SD (2009) High temperature fatigue of nickel-base superalloys - A review with special emphasis on deformation modes and oxidation. Eng Fail Anal 16:2668–2697. doi:10.1016/j.engfailanal.2009.01.010
7. Stinville JC, Echlin MP, Callahan PG, et al (2017) Measurement of strain localization resulting from monotonic and cyclic loading at 650 ∘C in nickel base superalloys. Exp Mech 57:1289–1309. doi:10.1007/s11340-017-0286-y



Description of the PhD project :

The present PhD project will focus on the multiscale mechanical characterisation of the graded TixAlyCr(1-x-y) and NixAlyCr(1-x-y) model materials, using HT-nanoindentation tests, micropillar compression tests, in-situ tensile testing paired with digital image correlation techniques. The goal of the PhD is to provide a quantitative evaluation of the elementary deformation mechanisms and chemical evolution of the surface grains. The identified properties will aim to feed further finite element models coupled with a phase-field models to address the mechano-chemical coupling operating at the sub-grain level. The PhD will investigate the elementary mechanisms of deformation within the oxidation-affected layer and the interaction with oxidation products.

In the present project, the PhD student will :
• Characterise the evolution of the oxidation-affected region in TixAlyCr(1-x-y) and NixAlyCr(1-x-y) model materials ;
• Characterise the micromechanical properties within the oxidation-affected region at different temperatures using HT-nanoindentation tests and micropillar compression tests ;
• Develop speckle patterns for high temperature digital image correlation techniques at the microscale ;
• Characterise intragranular slip events using high resolution digital image correlation techniques ;
• Characterise dislocation structures in the oxidation-affected region and non-affected region using post-mortem TEM analyses and/or in-situ TEM testing ;
• Analyse topographic images from high temperature experimental mechanical tests (holographic microscopy, confocal microscopy, scanning electron microscopy + tensile tests and mesoscale bulge tests) ;
• Analyse the oxidation products related to strain localisation inherent to various loading conditions (incremental tensile tests, fatigue tests, etc.) ;
• Develop and identify a model describing the formation and growth of strain-localisation- assisted oxides.

Work Context

The Institut Clément Ader (ICA, CNRS UMR 5312) is a research laboratory dedicated to the study of mechanical structures, systems and processes. Our sectors of activity fall within those of the mechanical industries, with particular attention paid to projects in the fields of aeronautics, space, transport and energy. Our work generally focuses on modelling the mechanical behaviour of materials, its instrumentation and the study of the durability of the structures or products considered.

The ICA has about 80 research professors, 20 temporary researchers, 20 administrative staff, 90 doctoral students, as well as many interns. With the particularity of having :
- at the level of the supervisory bodies, staff belonging to four major institutions: UPS and INSA from the Ministry of Higher Education and Research, ISAE from the Ministry of Defence, Mines Albi from the Ministry of Industry;
- geographically, the staff is spread over four cities in the Midi-Pyrénées/Occitanie region: Albi, Figeac, Tarbes and Toulouse.
The management is composed of a director and two deputy directors, the three supervisory ministries being represented in this trio. The technical support team (BIATSS staff) is organised into three components, one for each ministry.

The laboratory is organised into four research groups:
- MSC group: Composite Materials and Structures ;
- SUMO Group: Surface, Machining, Materials and Tools;
- MS2M Group: Modelling of Mechanical Systems and Microsystems;
- MICS Group: Metrology, Identification, Control and Monitoring.

This research work is in line with the research themes of the MICS and SUMO groups, for the understanding and metrological development associated with surface reactivity phenomena assisted by mechanical deformation.

PhD locations :
INSTITUT CLEMENT ADER
IMT-Mines Albi-Carmaux
Campus Jarlard
81013 Albi CEDEX 09, France

AND

CEMES
29 Rue Jeanne Marvig
31055 Toulouse, France

Constraints and risks

Mechanical testing at high temperature

Additional Information

This PhD work is part of the ERC Starting Grant - HT-S4DefOx: High temperature - small scale sub-surface deformation assisted by oxidation.

The desired candidate should have a Master's degree and a strong background in :
- Mechanical engineering (especially at the microscopic scale) ;
- Materials science and/or computational solid mechanics;
- Surface reactivity;
- Metallographic characterisation skills;
- Image analysis;
- Scientific computing (Matlab and/or Python language, etc.).

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