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Featured researches published by S. Mathieu.


Materials at High Temperatures | 2015

Environmental/thermal barrier coating systems deposited on Nb/Nb5Si3 based alloy

Reinhold Braun; Annika Lange; Uwe Schulz; Léo Portebois; S. Mathieu; Michel Vilasi; Stefan Drawin

Abstract Coupons of a Nb-silicide-based alloy with the nominal composition of 47Nb–25Ti–8Hf–2Cr–2Al–16Si (at-%) were coated with Co-, Ni- and FeB-modified M7Si6-based layers using pack-cementation. Subsequently, on one side of the coated samples, environmental/thermal barrier coatings (E/TBCs) of yttria partially stabilised zirconia (YSZ) and gadolinium zirconate were deposited by electron beam physical vapour deposition. The lifetimes of the different E/TBC systems were determined performing thermal cycling tests at 1100 and 1200°C in air. At 1100°C, lifetimes approaching 1000 cycles (corresponding to 1000 h of high temperature exposure) were measured. However, severe oxidation occurred at the edges and rear side of the samples (areas without ceramic topcoat) due to local degradation of the oxidation protective coatings, resulting in substantial material recession with prolonged testing. When thermally cycled at 1200°C, the E/TBC systems exhibited lifetimes exceeding 200 cycles. The sample with FeB containing bond coat and Gd2Zr2O7 topcoat survived even 400 cycles at this exposure temperature.


Materials at High Temperatures | 2015

Y2SiO5 environmental barrier coatings for niobium silicide based materials

Annika Lange; Reinhold Braun; Peter Mechnich; Claudia Büttner; Uwe Schulz; Léo Portebois; S. Mathieu; Michel Vilasi; Stefan Drawin

Abstract The oxidation behaviour of Nb silicide based alloys, considered as potential ultra-high temperature material for gas turbine engine applications, can be improved by chromia–silica forming coatings with M7Si6 structure. To stabilise the protective oxide scales against water vapour corrosion in combustion atmospheres, environmental barrier coatings (EBCs) of yttrium silicate were deposited on an FeB modified M7Si6 based bond coat using magnetron sputtering. The 15–20 μm thick ceramic top coats with an approximate chemical composition of 25Y–13Si–62O (at.-%) were dense and amorphous after deposition. They were annealed in vacuum to get a crystalline structure with the predominant phase Y2SiO5. Samples with this EBC system were tested in rapidly flowing water vapour at temperatures between 1100 and 1300°C for up to 16 h. At 1100 and 1200°C, significantly reduced mass gains were determined for samples with yttrium silicate top coat in comparison to those coated only with FeB containing layers. The EBC partially transformed into the Y2Si2O7 phase and exhibited microporosity. At 1300°C, the yttrium silicate layer decomposed forming yttrium oxides.


The Open Corrosion Journal | 2011

Chromium Deposition on Cobalt-Based Alloys by Pack-Cementation and Behaviour of the Coated Alloys in High Temperature Oxidation

Grégory Michel; Patrice Berthod; S. Mathieu; Michel Vilasi; Pierre Steinmetz

Two TaC-strengthened cobalt-based alloys, with compositions Co-10Cr-0.25C-4.4Ta and Co-10Cr-0.5C-8.7Ta (wt.%) underwent Cr-deposition by pack-cementation, followed by heat-treatment to allow Cr diffusing deeper in their sub-surface. Thereafter they were tested for 50 hours at 1200°C in a thermobalance. These alloys were successfully enriched in chromium, with a maximal content on surface of about 30wt.% and a depth of enrichment of several hundreds of micrometers. This allowed a chromia-forming behavior of the cemented alloys despite the 10wt.%Cr of the bulk. This was especially true for the {C,Ta}-richest alloy the oxidation kinetic of which was wholly parabolic and analogous to a Ni-30Cr alloy known for its good behavior in oxidation at 1200°C. The parabolic constants and chromia-volatilization constants were at the same levels of the Ni-30Cr ones. However, the chromium enrichment step, especially the diffusion heat-treatment following the cementation, causes fragmentation and surface fraction reduction of the tantalum carbides which strengthen the alloy.


Materials at High Temperatures | 2018

About the control of semiconducting properties of chromia: investigation using photoelectrochemistry and orientation mapping in a TEM

Laurence Latu-Romain; Y. Parsa; M. Ollivier; S. Mathieu; Michel Vilasi; G. Renou; F. Robaut; Y. Wouters

Abstract The semiconducting properties of chromia, studied by photoelectrochemistry (PEC), are varied by oxidizing pure Cr as a function of temperature and oxygen activity. At 800 °C and a p(O2) of 10-14 atm, a single n-chromia is observed, while at 900 °C and a p(O2) of 10-12 atm a n- & p-layer is obtained. For intermediate conditions, an insulating stoichiometric Cr2O3 is identified at 850 °C for a p(O2) of 10-13 atm. The TEM investigation reveals a duplex morphology for every scales: an equiaxed (resp. columnar) morphology has been developed in the internal (resp. external) part. Between these two subscales, a textured chromia layer has been identified as the first layer to form. Finally, the association of TEM and PEC techniques permits the identification of major point defects. It is revealed that the morphology is only linked to the growth direction: anionic (resp. cationic) growth leads to equiaxed (resp. columnar) grains.


Materials at High Temperatures | 2015

Kinetic and metallographic study of oxidation at high temperature of cast Ni 25Cr alloy in water vapour rich air

Lionel Aranda; Thierry Schweitzer; Ludovic Mouton; S. Mathieu; O. Rouer; Pascal Villeger; Patrice Berthod; Elodie Conrath

Abstract The high temperature oxidation behaviour of a Ni–25 wt-%Cr alloy in air enriched with water vapour (180 mbars H2O) was studied at 1000, 1100, 1200 and 1300°C. The oxidised samples were characterised by X-ray diffraction, electron microscopy and wavelength dispersion spectroscopy. The obtained data were compared to the ones earlier obtained for the same alloy oxidised in dry air. Water vapour globally induced at all temperatures a decrease of the parabolic constant Kp and an increase in the chromia volatilisation constant Kv. The oxide scales do not present morphologic difference between the two atmospheres. After oxidation in humidified air the scale thickness is thinner and the Cr depleted depth is lower than in dry air.


Journal of Materials Engineering and Performance | 2018

Correlation Between the Pitting Potential Evolution and \(\varvec\sigma\) Phase Precipitation Kinetics in the 2205 Duplex Stainless Steel

Mustapha Djama; Djaffar Saidi; Abdelaziz Kadri; Nabil Kherrouba; Brahim Mehdi; S. Mathieu; Thierry Schweitzer; Idir Brahim

The aim of this work is to correlate the pitting potential (Epit) evolution with the kinetics of σ phase precipitation in the 2205 duplex stainless steel aged at 850 °C after solution treatment at 1150 °C. The potentiodynamic polarization curves indicate a reduction of the pitting corrosion resistance with the aging time, which is revealed by a decrease in the Epit values from 0.65 to 0.40 VSCE. Thus, Epit values are used to determine the kinetics parameters of the σ phase precipitation. The experimental transformed fraction agrees well with the one calculated by using the modified Kolmogorov–Johnson–Mehl–Avrami equation with an impingement parameter c = 0.6.


Corrosion Science | 2012

On the oxidation mechanism of niobium-base in situ composites

S. Mathieu; S. Knittel; Patrice Berthod; Michel Vilasi


Calphad-computer Coupling of Phase Diagrams and Thermochemistry | 2003

Experimental and thermodynamic study of the microstructure evolution in cobalt-base superalloys at high temperature

Patrice Berthod; S. Michon; L. Aranda; S. Mathieu; J.C. Gachon


Intermetallics | 2011

The oxidation behaviour of uniaxial hot pressed MoSi2 in air from 400 to 1400 °C

S. Knittel; S. Mathieu; Michel Vilasi


Solid State Sciences | 2007

Inhibitors for magnesium corrosion: Metal organic frameworks

Adel Mesbah; Caroline Juers; Françoise Lacouture; S. Mathieu; Emmanuel Rocca; Michel François; Jean Steinmetz

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Michel Vilasi

Centre national de la recherche scientifique

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Michel Vilasi

Centre national de la recherche scientifique

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N. Chaia

University of Lorraine

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Laurence Latu-Romain

Centre national de la recherche scientifique

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Y. Wouters

Centre national de la recherche scientifique

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