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Portail > Offres > Offre UMR5312-DAMTEX-006 - [H/F] Postdoc en Évaluation expérimentale et numérique de la localisation des déformations dans les alliages à base de Ti et de Ni affectés par l'oxydation

[M/F] Postdoc in Experimental and numerical assessment of strain localisation in oxidation-affected Ti and Ni-based alloys

This offer is available in the following languages:
Français - Anglais

Date Limite Candidature : mardi 27 avril 2021

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General information

Reference : UMR5312-DAMTEX-006
Workplace : TOULOUSE
Date of publication : Tuesday, April 06, 2021
Type of Contract : FTC Scientist
Contract Period : 12 months
Expected date of employment : 1 December 2021
Proportion of work : Full time
Remuneration : Between 2648 and 3768€ gross per month depending on the experience
Desired level of education : PhD
Experience required : 1 to 4 years

Missions

Context :

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 Postdoc project :

The present PostDoc fellowship will focus on the mechanical characterisation of the graded NixAlyCr(1-x-y) and TixAlyCr(1-x-y) model materials using HT-nanoindentation, micropillar compression tests and digital image based-modelling and correlation (DIC) techniques to evaluate strain localization at the sub-grain level.

In the present project, the PostDoc fellow will :
• Reconstruct 3D data sets of polycrystalline materials from images (sinograms and/or stack of section images)  3D segmentation using voxels ;
• Mesh of the 3D segmented microstructure ;
• Model and simulate crystal plasticity on the reconstructed microstructure;
• Perform experimental mechanical tests at the micro-scale: HT-nanoindentation tests, HT-mesobuldge tests and HT-tensile tests monitored using full-field measurements ;
• Analyse topographic images from high temperature experimental mechanical tests (holographic microscopy, confocal microscopy, scanning electron microscopy) ;
• Develop numerical tools for assessing discontinuities in kinematic fields ;
• Model the intensity evolution of the speckle pattern based on oxidized surfaces ;
• Develop assimilation techniques based on 3D models from 3D surface measurements ;
• Simulate and compare kinematics fields in the volume from surface boundary measurements.

Activities

• Reconstruct 3D data sets of polycrystalline materials from images (sinograms and/or stack of section images)  3D segmentation using voxels ;
• Mesh of the 3D segmented microstructure ;
• Model and simulate crystal plasticity on the reconstructed microstructure;
• Perform experimental mechanical tests at the micro-scale: HT-nanoindentation tests, HT-mesobuldge tests and HT-tensile tests monitored using full-field measurements ;
• Analyse topographic images from high temperature experimental mechanical tests (holographic microscopy, confocal microscopy, scanning electron microscopy) ;
• Develop numerical tools for assessing discontinuities in kinematic fields ;
• Model the intensity evolution of the speckle pattern based on oxidized surfaces ;
• Develop assimilation techniques based on 3D models from 3D surface measurements ;
• Simulate and compare kinematics fields in the volume from surface boundary measurements.

Skills

The postdoc fellow should have the following skills and/or know-how:
• Material sciences and computational solid mechanics ;
• Integrated experimental-numerical approach ;
• Image analysis (image segmentation, image-based models, 3D reconstruction from sinograms and/or stack of images, 2D- and stereo-DIC, etc.) ;
• Nanoindentation skills (experimental or numerical) ;
• Scientific computing (Python language, HPC, etc.).

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, SUMO and MS2M groups, for the understanding and metrological development associated with surface reactivity phenomena assisted by mechanical deformation.

Postdoc locations :
INSTITUT CLEMENT ADER
IMT-Mines Albi-Carmaux
Campus Jarlard
81013 Albi CEDEX 09, France
AND
INSTITUT CLEMENT ADER
3, rue Caroline Aigle
F-31400 Toulouse CEDEX 04, France

Constraints and risks

Use of computers

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