Michel Vilasi

Michel Vilasi
University of Lorraine | UdL · Faculty of Sciences and Technologies

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192
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Publications

Publications (192)
Article
Hot corrosion of metals and alloys is one of the main causes of degradation of aeronautical and land turbine parts as well as components of waste-to-energy plants. This form of degradation is often more severe than dry oxidation and results in the formation of a corrosive deposit on the surface of the parts and attacks the alloy and its protective...
Article
Metal alloys produced by additive manufacturing have specific microstructures and compositions. Their microstructure is generally out of equilibrium, textured, and inhomogeneities can be observed. They can have pores and nano-inclusions. The contents of volatile elements may deviate from the nominal composition. These alloys often experience signif...
Article
The molar heat capacities of the Fe2Nb and Fe7Nb6 intermetallic compounds are reported here for the first time. The results were obtained via Differential Scanning Calorimetry (DSC) measurements, performed in a temperature range between 348 and 1038 K. The alloys were prepared by arc-melting high purity metals under argon flux and later heat-treate...
Article
Interactions between a metal and a molten glass involve two main phenomena, namely, sticking and corrosion. A physicochemical approach is proposed here to study and understand the influence of the relevant parameters on these interactions: temperature (which controls kinetics and reactivity), glass composition (as basicity controls oxo‐complexation...
Article
A model of dissolution of chromia in binary Na2O-SiO2 liquids is presented in this work. Data available in the literature on the acid/base properties and the chemistry of chromium in such liquids were used in order to refine the model. Physical phenomena such as migration of ions and the resulting electric field, the mechanical equilibrium of the l...
Article
Corrosion tests of Ni-30Cr alloy were performed in three simplified soda-silicate and borosilicate melts in order to follow the evolution of the protective chromia layer. A complete identification of the corrosion mechanisms enables the establishment of a kinetic model based on the oxide formation and dissolution rates. The dissolution kinetics is...
Article
Corrosion resistance of nickel based alloys in molten silicates is linked to the temperature. Above a certain temperature, the protection of the alloy by a chromia layer is no more ensured: this depassivation phenomenon leads to active corrosion. Electrochemical methods were used for in situ characterization, and Scanning Electron Microscopy (SEM)...
Article
Full-text available
In this work a re-investigation of the solubility limits of the (Nb), Nb3Al, Nb2Al and the Nb-rich side of the NbAl3 phases on the Nb-Al system is presented. Alloys in the binary fields ((Nb)+Nb3Al, Nb3Al+Nb2Al and Nb2Al+NbAl3) were arc-melted, and then equilibrated at 1000, 1200 and 1400 °C. The phases were confirmed via X-ray powder diffractometr...
Article
The microstructure and oxidation resistance of Laser Beam Melted (LBM) and Conventionally Manufactured (CM) Inconel 625 alloys were studied at 900 °C and 1050 °C. The microstructure of the LBM samples was cellular, with Nb and Mo segregations located at the cell walls. At 900 °C, the oxidation rate was similar for both materials but was clearly hig...
Article
Dissolution of different rare earth oxides RE2O3 and cyclosilicate Ca3RE2(Si3O9)2 was studied at 1200 °C in a pseudo-ternary CAS melt. This investigation is relevant to CMAS resistant thermal barrier coatings (TBC) used in aircraft engines. CMAS is a generic term for the molten siliceous deposits resulting from the ingestion of mineral particles wi...
Article
The energetic stability and oxidation behaviour of quaternary chromium silicides mainly depends on their chromium content. In this work, the pseudolamellar crystal structures of six representatives of the X3T2(T1-xCrx)2Si6 compounds (X = Nb or Ti and T = Fe, Co or Ni) are determined by resonant X-ray diffraction using the synchrotron facility, comb...
Article
In the present work, the Ta-B system was thermodynamically optimized based on the CALPHAD method using data of liquidus temperatures, invariant transformations and enthalpy of formation from the literature as well as new experiments performed in our group. The phases Ta3B2, TaB(rt), Ta5B6, Ta3B4 were modeled as stoichiometric compounds. On the othe...
Article
Full-text available
The short-term oxidation behaviour of RA 602CA, Inconel 693, Manaurite 40XO and Sumitomo 696, which are four alloys recommended for hydrocarbon processing, was studied both in air and in Ar–H2O to determine the conditions of pre-oxidation treatments. Regardless of the considered material, the oxidation rate at 950 °C was systematically higher in Ar...
Article
The relationship between the corrosion behavior of a Ni-30Cr alloy and the physicochemical properties of chromium in silicate and borosilicate melts at 1150 °C has been investigated. Three glass compositions have been chosen in order to identify the effect of basicity and viscosity. The chromium solubility limits in borosilicate melts have been det...
Article
Environmental/thermal barrier coatings (E/TBCs) were applied on an Nb/Nb5Si3-based alloy. The substrate material with the nominal composition Nb-23Ti-4Hf-3Cr-6Al-20Si (at.%) was manufactured by plasma melting. Rectangular platelets of this alloy were coated with chromia-silica forming M7Si6-based (M = Ti, Nb, Cr, X with X = Ni, Co, Fe) bond coats p...
Article
In the present work, the V-Si-B ternary system was thermodynamically modeled using the CALPHAD method. The thermodynamic descriptions of the V-Si and B-Si binary systems were taken from literature while the parameters of binary V-B were re-evaluated, based on new experimental information. The ternary thermodynamic description was based on experimen...
Article
Full-text available
The high-temperature oxidation behavior of a binary Ni-30Cr model alloy has been studied at 1050 °C at three oxygen partial pressures p(O2): ~10−14, ~10−10, and ~10−5 atm. The oxide scales were characterized using grazing X-Ray diffraction, Raman spectroscopy, EDX spectroscopy, and TEM microscopy. The semiconducting properties of the oxide scale ha...
Article
Full-text available
The oxidation behaviour of Ti3(Ni,Cr)3CrSi6 and Ti4Ni4Si7 was studied in air both at 1000 and 1100 °C. The formation of the oxidation products and the phase transformation were characterized by in situ X-ray diffraction and SEM-FEG post-mortem observations. The crystal structure of Ti3(Ni,Cr)3CrSi6 was also determined using powder X-ray diffraction...
Article
Full-text available
Nickel and iron aluminide coatings were identified as possible candidates for hardfacing materials in Sodium Fast Reactors. Both coatings were developed on two steel grades of interest for the next French Sodium Fast Reactor prototype, 316L(N) and T91. Pack cementation and slurry were employed as aluminization processes. The compatibility of all co...
Article
The possibility to tune the semiconducting properties of chromia scales thermally grown on pure chromium as a function of temperature and oxygen partial pressure p(O2) has been demonstrated in the present paper. While at 800 °C and a p(O2) of 10⁻¹⁴ atm, a single n-chromia is observed, at 900 °C and a p(O2) of 10⁻¹² atm, a duplex n- and p-chromia is...
Article
High temperatures solid-liquid equilibria in the Cr-Nb-Si system are poorly known in the Si-rich area (>20% at Si). In this study, twenty-two as-cast samples were prepared and fully characterized using X-ray diffraction, scanning electron microscopy and quantitative energy dispersive spectrometry. Obtained results lead us to propose a new schematic...
Article
Improvement of the calcium-magnesium aluminosilicate (CMAS) infiltration mitigation concept in thermal barrier coatings (TBC) requires fundamental data on thermochemical reaction involving rare-earth oxide candidate as ZrO2 alloying element. This study investigates, through a model approach, Gd2O3 dissolution at 1200 °C in a synthetic model CAS mel...
Article
Full-text available
Chromia grown on pure chromium at 900 °C for 30 min at an oxygen partial pressure p(O2) of 10−12 atm has been characterized using photoelectrochemical and electron microscopy techniques. This study reveals a duplex scale: n-chromia with equiaxis morphology in the internal part (~650 nm thick) and p-chromia with columnar morphology in the external p...
Article
To provide protection against corrosion at high temperatures, silicide diffusion coatings were developed for the V-4Cr-4Ti alloy, which can be used as the fuel cladding in next-generation sodium-cooled fast breeder reactors. The multilayered coatings were prepared by halide-activated pack cementation using MgF2 as the transport agent and pure silic...
Article
Environmental/thermal barrier coatings (E/TBCs) of yttria partially stabilised zirconia (YSZ), gadolinium zirconate (GZO) and a combination of Y2SiO5 and GZO were applied on a Nb/Nb5Si3-based alloy with the nominal composition of Nb-25Ti-8Hf-2Cr-2Al-16Si (at%). A B-containing M7Si6-based (M = Ti, Nb, Fe, Cr) layer produced by pack cementation was u...
Article
Full-text available
Corrosion by molten phases leads to severe corrosion of heat exchangers in waste-to-energy plants. In addition, the presence of heavy metal chlorides in ash deposit increases degradation at low temperature due to the formation of highly corrosive molten phases. In this study, two heat exchanger materials, a low alloy steel (16Mo3) and a nickel base...
Article
The oxidation behaviour of Ni-30Cr alloy and the kinetics of the sole growth of Cr2O3 have been studied at 1150 °C up to 289 h at oxygen pressures comprised between 10−13 and 10−3 atm, thanks to Rhines pack device. Oxide morphology, growth mechanisms and kinetics are discussed in terms of nature, concentration and diffusion of point defects. The cr...
Article
The formation of protective Cr2O3 layer on Ni-Cr alloys depends on (i) the chromium concentration at the alloy/oxide interface and (ii) the chromium diffusion in the alloy from the core towards the surface. A sufficient interfacial chromium content and chromium gradient are necessary to sustain the selective external oxidation of chromium. Ni-30Cr...
Article
Full-text available
A comparison of the corrosion behaviour of simplified chromia- and alumina-forming alloys (Ni-30Cr and Ni-8Al-28Cr) in molten glass is performed via electrochemical methods. A pre-oxidation treatment in air prior to immersion ensured the formation of a 2-μm-thick oxide scale of Cr2O3 or Al2O3. The lifetime of Ni-30Cr depended on the competition bet...
Article
The oxidation resistance of MSi2 compounds with M = V, Ti, Cr was investigated from 450 to 950 °C in air under isothermal and cyclic conditions. Vanadium, chromium and titanium disilicide were not subjected to the pest phenomenon at 650 °C over 800 1-h cycles. The results demonstrated very low weight gains regardless of the testing conditions. Oxid...
Article
The corrosion characteristics of model chromia-forming alloys (i.e. pure Cr and Ni–30 wt%Cr alloy) were studied in molten soda–lime–silicate (i.e. Na2O–CaO–xSiO2, x = 3 or 6, molar composition) at 1100 and 1150 °C using electrochemical techniques coupled with ex situ observations. High Cr activity of pure Cr led to high corrosion rates and also the...
Article
The PbO–Al2O3 system has been extensively studied in literature. In the present study, experimental work was conducted in which equilibria between phases were investigated under air between 600 °C and 800 °C by X-ray diffraction. Three intermediate compounds reported in literature were confirmed, which are PbAl12O19 (1PbO:6Al2O3), PbAl2O4 (1:1) and...
Article
In this work, an extensive study was carried out on the preparation and characterization of nanoclay biocomposites based on cellulose to substitute for synthetic polymer foam trays as food-packaging materials. The preparation stage was performed via a dissolution/regeneration route followed by drying with lyophilization. The chemical, physical, mec...
Article
In the present work, an assessment of the V–Cr–Si system was done. Mainly based on previously ternary experimental data on the isothermal section at 1200 °C and on the liquid–solid equilibria, a thermodynamic modeling of the ternary system was performed within the CALPHAD approach using the Thermo-Calc and the Pandat software packages and taking in...
Article
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 (...
Article
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 zir...
Article
Molten silicate glasses are complex media in which ionic species can be easily dissolved. That typically concerns the metallic cations or oxoanions. The as-described liquids have therefore the properties of electroactive solutions in which the ions displacements allow the electrical conduction. As a consequence, the use of electrochemical technique...
Article
In the present work, liquid-solid phase equilibria of the V-Cr-Si phase diagram were experimentally studied. The samples were prepared by arc melting and as-cast microstructures were characterized by SEM, WDS and XRD. No new ternary phase was observed. Seven primary solidification regions were identified in these alloys: (V,Cr) solid solution, M3Si...
Article
V–4Cr–4Ti vanadium alloy is a potential cladding material for sodium-cooled fast-neutron reactors (SFRs). However, its affinity for oxygen and the subsequent embrittlement that oxygen induces causes a need for an oxygen diffusion barrier, which can be obtained by manufacturing a multi-layered silicide coating. The present work aims to evaluate the...
Article
The system Bi2O3–Al2O3 has been experimentally investigated above 600 °C by DTA, XRD and EPMA under air and low oxygen pressure. Only two compounds were found to exist in equilibrium, which are Bi2Al4O9(1Bi2O3:2Al2O3) and Bi25AlO39(25:1). The latter exhibits a sillenite structure and does not contain pentavalent bismuth. A peritectoid decomposition...
Article
The present work is focused on the oxidation at 1050°C of a model chromia-forming alloy, paying attention to the control of the oxygen partial pressure. Following an original approach, supported by a robust fitting of experimental results, photelectrochemical characterization has revealed an unexpected number of oxide phases in the scale at low P(O...
Article
In the present work, the isothermal section at 1200 °C of the V–Cr–Si phase diagram was experimentally studied. The samples were prepared by arc melting and characterized using scanning electron microscopy/energy-dispersive spectroscopy and electron probe microanalyzer. The continuous solution phases (Cr,V)3Si, (Cr,V)5Si3 and (Cr,V)Si2 were confirm...
Article
This paper reports the effects of adding from 2 to 8 at.% tin on the oxidation behaviour of Nb/Nb5Si3 composites at 815°C and at higher temperatures (1100 and 1200°C). The role of tin in the elimination of pesting and in the oxidation process at high temperatures was established. The consumption of elements with a higher affinity for oxygen than Sn...
Article
This paper reports the effect of adding 2 to 8 at.% Sn on the microstructure of Nb-25Ti-8Hf-2Cr-2Al-16Si. The samples were synthesised by casting and were heat treated for 5 days at 1200°C. The as-cast and heat-treated microstructures were characterised using X-ray diffraction, scanning electron microscopy and microprobe analysis. The results revea...
Article
Rhenium (Re) is used as an alloying element in Ni based superalloys but promotes the formation of fragile intermetallic compounds in many systems. The thermodynamic databases that allow the modeling of the properties of Ni based alloys are still incomplete and further data has to be integrated. In this context, we propose a new characterization of...
Conference Paper
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 (...
Article
Full-text available
The solubility of chromium oxide (Cr2O3) in soda lime silicate glasses was studied as a function of temperature (1,200 °C ≤ T ≤ 1,350 °C), oxygen fugacity (−12 ≤ log fO2 ≤ −0.6) and glass composition (Na2O–CaO–xSiO2; x = 3, 4, 5 and 6). The fO2 was proved to induce several oxidation states of Cr for a given glass composition at a fixed temperature....
Article
The dissolution equilibrium of chromium oxide (Cr2O3) in a soda lime silicate melt (Na2O-CaO-5SiO(2)) at 1300 degrees C was studied in two extreme atmospheres. The samples were subjected to oxidizing (fO(2) = air) and reducing (fO(2) = Fe/FeO buffer) atmospheres. The equilibrium was expected to be achieved when there was no significant difference o...
Article
The present study focuses on the oxidation mechanism of Nb-silicide composites and on the effect of the 29 composition on the oxidation rate at 1100 �C. A theoretical approach is proposed based on experimental 30 results and used to optimise the oxidation resistance. The growth model based on multiphase diffusion 31 was experimentally tested and co...
Article
Full-text available
Intermetallic single phases (TiXCr)7Si6 (with X = Fe, Co or Ni) were manufactured by uniaxial hot pressing. Their full characterization (SEM + XRD) highlighted that the nature of the metal constituent X influenced the chromium content in the silicide compositions. Both isothermal and cyclic oxidation studies at a temperature as high as 1300 °C evid...
Article
The oxidation resistance and the crystal structure of the new Ti4NiSi4 compound were investigated. This compound was manufactured both as a single-phase and as the outer layer of a protective coating for vanadium alloys. The recorded oxidation rates were very low at 650 degrees C and 750 degrees C in air, which represents a more severe environment...
Article
In thiswork,we describe the fabrication of coatings containing (TiNbXCr)7Si6 silicide (with X = Fe, Co andNi) by halide-activated pack-cementation on Nb and silicide composites. The coating oxidation performance is evaluated isothermally at temperatures ranging from 1100 °C to 1300 °C and cyclically at 1100 °C. In all the coating systems examined,...
Article
This study focuses on the oxidation behavior of commercially available HR120 in air at 1,050 °C from 30 min to 100 h. The oxidation kinetics were first studied by thermogravimetry and isothermal exposure. The oxidation products were fully characterized using ex and in situ X-ray diffraction (XRD) and FEG-SEM observations. HR120 experienced at 1,050...
Conference Paper
Full-text available
The present work is dedicated to the description of the pseudo-binary Al2O3-Bi2O3 and the isothermal section at 600°C of the system Al2O3-Bi2O3-PbO according to a Calphad approach. It takes part of the complete description of the complex system Pb-Bi-Fe-(Al,Cr)-O. Such study is of high interest for the nuclear community that aims to develop protect...
Article
This study focuses on the development of new protective coatings for the vanadium-based alloy V-4Cr-4Ti. Halide-activated pack-cementation (HAPC) technique was used to develop VxSiy multilayered diffusive silicide coatings. The outer layers (coatings) were formed of VSi2 doped with 27 at.% Cr or TiSi2. These compounds exhibited a very low oxidation...
Article
The Metal And Silicide Composite (MASC), having the composition Nb–25Ti–8Hf–2Cr–2Al–16Si, at.%, was studied in static oxidising condition in air at 815, 1100 and 1200 °C. Phases present were Nb solid solution and Nb5Si3. Pesting did not occur at 815 °C before 100 h of exposure while internal oxidation took place at each temperature and affected the...