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The oxidation behavior of Si- and/or Mn-Ni-25Cr alloys at 1050 °C in air was studied to provide new insights on the effect of minor additions on chromia-scale growth. Four nickel alloys with and without Si or Mn were prepared. Thermogravimetry and post-oxidation characterizations evidenced that manganese increased, whereas silicon addition decreased chromia growth rate. On the contrary, addition of both Si and Mn to the Ni-25Cr alloy led to an unchanged oxidation rate in comparison with the unalloyed Ni-25Cr material. Oxide scales were characterized by photoelectrochemistry (PEC) to evaluate the role of the additions on the point defects nature. The n and p contributions of chromia forming in air were not changed by Si. On the opposite, Mn modified the scale conducting properties since only n contributions were observed for both chromia and Mn1+xCr2−xO4 spinel oxide with Mn-containing samples. In the latter case, the PEC contribution at ~ 3.2–3.4 eV was allocated to the signature of the Mn1+xCr2−xO4 spinel oxide. These data suggested that manganese enhances and silicon limits grain boundary diffusion in chromia scale as reactive element does.

Background Owing to growing number of therapeutic options with similar efficacy and safety, we compared the acceptability of therapeutic maintenance regimens in inflammatory bowel disease (IBD). Methods From a nationwide study (24 public or private centers), IBD patients were consecutively included for 6 weeks. A dedicated questionnaire including acceptability numerical scales (ANS) ranging from 0 to 10 (highest acceptability) was administered to both patients and related physicians. Results Among 1850 included patients (65.9% with Crohn’s disease), the ANS were 8.68 ± 2.52 for oral route (first choice in 65.8%), 7.67 ± 2.94 for subcutaneous injections (first choice in 21.4%), and 6.79 ± 3.31 for intravenous infusions (first choice in 12.8%; P < .001 for each comparison). In biologic-naïve patients (n = 315), the most accepted maintenance regimens were oral intake once (ANS = 8.8 ± 2.2) or twice (ANS = 6.9 ± 3.4) daily and subcutaneous injections every 12 or 8 weeks (ANS = 7.9 ± 3.0 and ANS = 7.2 ± 3.2, respectively). Among 342 patients with prior exposure to subcutaneous biologics, the preferred regimens were subcutaneous injections (≥2 week-intervals; ANS between 9.1 ± 2.3 and 8.1 ± 2.7) and oral intake once daily (ANS = 7.7 ± 3.2); although it was subcutaneous injections every 12 or 8 weeks (ANS = 8.4 ± 3.0 and ANS = 8.1 ± 3.0, respectively) and oral intake once daily (ANS = 7.6 ± 3.1) in case of prior exposure to intravenous biologics (n = 1181). The impact of usual therapeutic escalation or de-escalation was mild (effect size Conclusions Although oral intake is overall preferred, acceptability is highly impacted by the rhythm of administration and prior medication exposures. However, SC treatment with long intervals between 2 injections (≥8 weeks) and oral intake once daily seems to be the most accepted modalities.

A test rig consisting of a quartz tube placed in a horizontal furnace made of five independently regulated heating zones allowed the evaluation of the metal dusting attack of a FeNiCr alloy. Fifteen samples were exposed in a temperature gradient from 504° to 704°C, 1.1 bar, to a highly carburizing atmosphere for 1500 h. Below 561 °C the high density of pits led to uniform corrosion whereas localized pits developed at higher temperatures. In depth pit growth rate raised to a maximum at 632 °C, then decreased showing that it depends both on temperature and on the carbon activity gradient.

International audience; Oxidation of chromia-forming alloys (pure chromium, nickel–chromium alloy and ferritic stainless steel alloy) at temperature ranging from 800 to 1050 °C was conducted on samples with or without gold markers applied prior to testing. Gold is often used as a marker in order to identify oxide growth direction. Its localization inside the oxide scale can demonstrate an inward or an outward growth. It is found that gold particles can be found either at the internal metal/oxide interface or inside the scale or again at the external oxide/gas interface on the same sample (on NiCr and stainless steel alloys). For pure chromium oxidation, gold is found inside the chromia scale, at the equiaxed-columnar interface, as expected from ASTAR-TEM characterization. However, photoelectrochemical characterization has shown that gold can modify the semiconducting chromia properties. Finally, gold is not inert in these several conditions and should not be considered in these present cases, but also more generally in most cases, as an appropriate marker. On the contrary, ASTAR maps may permit to access the oxide growth direction without interfering the studied system.

International audience; The aim of this work is to show the influence of the gaseous environment on the ferritic Fe-Cr-Si model alloy oxidation during 70 h, at 900 °C and 950 °C. Two different atmospheres have been used: air or nitrogen containing 5 Vol.% hydrogen (N 2-5%H 2). After air oxidation, a non-adherent chromia scale formed. In the N 2-5%H 2 gaseous environment, it clearly appears that silicon segregation near the internal scale-metal interface is favoured. In this low oxygen containing gas, adherent chromia and silica scales have been formed. Silica subscale associated to an adherent chromia scale obtained in low oxygen conditions are a good protection barrier against carburisation.

In the present study, the effect of microstructure and precipitation phenomena on the micro hardness, tensile strength, impact toughness, and electrochemical behavior of tungsten inert gas (TIG)-welded AA6061-T6 aluminum alloy are investigated. The microstructure features showed mainly the grains of aluminum solid solution with the presence of some precipitates at the grain boundaries. Scanning electron microscope micrographs exhibited the presence of Fe-based intermetallic and β-equilibrium precipitates throughout α-Al grains. In the heat-affected zone (HAZ), the dissolution, over-aged, and coalescence of precipitates are observed; their hardening effects disappear and a decrease in strength and hardness are noticed. The fracture toughness values of each zone at different temperatures using Charpy V-notch test remained constant where the HAZ presents the highest absorbed energy. However, the temperature did not have a significant effect on the absorbed energy for each zone. In addition, the fractured surface of base metal (BM) and HAZ are characterized by dimple-like structure and they are larger in the HAZ. The electrochemical behavior of each zone of the weld evaluated in NaCl + H2O2 solution revealed that the corrosion current density of BM and HAZ is lower than that of molten zone (MZ), which displays high corrosion current density in this electrolyte and would be fastest to corrode.

A new high temperature detector dedicated to the collection of backscattered electrons is used in combination with heating stages up to 1050°C, in high vacuum and low vacuum modes in order to evaluate its possibilities through signal-to-noise ration measurements and different applications. Four examples of material transformations occurring at high temperature are herein reported: grain growth during annealing of a rolled platinum foil, recrystallization of a multi-phased alloy, oxidation of a Ni-based alloy and complex phase transformations occurring during the annealing of an Al-Si coated boron steel. The detector could be potentially adapted to any type of SEM and it offers good opportunities to perform high temperature experiments in various atmospheres. This article is protected by copyright. All rights reserved.

To clarify the influence of manganese on the oxidation behavior of Ni–Cr alloys, high resolution transmission electron microscopy was used to examine the microstructure and chemistry of oxide scales forming at 1050 °C on Ni–25Cr–xMn (x = 0.5, 1 and 1.5% wt) in 200 Pa O2. The scales consisted of two layers of chromia and one layer of spinel Mn1+xCr2-xO4. The internal layer exhibited an equiaxed grain structure, whereas columnar grains developed in the outer layer. The results demonstrated that the spinel composition at the chromia-spinel interface was similar regardless of the manganese concentration.

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.

Pure chromium oxidized at 900 °C at low oxygen partial pressure (10−12 atm) gives duplex Cr2O3 scale with an internal part made of equiaxed grains and exhibiting an n-type conduction, and an external part made of columnar grains and exhibiting a p-type conduction. Spalled regions occurring during cooling have been studied with photoelectrochemical techniques at a microscale. New information in the form of a specific image (structural quality image) could be obtained and revealed a level of structural defect density in the internal chromia subscale higher than that measured in the non-spalled region. The results complement the spallation scenario proposed in part I of this work.

In order to develop a potential route to fabricate plates and clips for orthopedic applications, a Mg–3.4Dy–0.2Zn–0.4Zr (wt.%) alloy was produced and analyzed in different conditions: solution treated at 525 °C for 3 h, hot rolled and hot rolled and aged at 250 °C. The aging behavior of the rolled alloy was investigated during isothermal aging at 250 °C, and a significant peak was observed at 10 h. The electrochemical behavior was evaluated in 0.9 wt.% NaCl solution at 37 ± 0.5 °C by potentiodynamic polarization and electrochemical impedance spectroscopy. The 525 °C-3 h and hot rolled specimens exhibited corrosion rates of 2.0 and 1.7 mm/year, respectively. The hot rolled and aged at 250 °C for 10 h specimen presented a grain size of 11.8 ± 1.7 μm with an intense macrotexture of the basal {0002} plane, hardness of 73 ± 3 HV and higher impedance modulus and obtained the highest corrosion resistance with a corrosion rate of 0.9 mm/year.

Chromia forming Alloy 718 and AD730™ have been submitted to isothermal long-term air exposure up to 10 000 h at 700 °C. The resulting very low specific mass gain led to consider two alternatives to determine the oxidation kinetics. Measurements of the external layer thickness and of the intergranular oxide amount were carried out on SEM micrographs evidencing the intergranular oxidation contribute around 30% to the total specific mass change. AD730™ with a thicker external scale and a higher amount of intergranular oxide showed a twofold faster oxidation rate than Alloy718. The results demonstrated the need of even longer tests.

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–H2O than in dry air. Surface examination of the Al-containing alloys indicated that they were not uniformly oxidized all over the surface. All Al-containing alloys (from 1.6 to 3.2% wt) formed an external protective alumina scale and behaved as alumina-forming alloys in dry air at 950 °C. In contrast, these alloys developed a rate-controlling chromia scale and severe internal oxidation in a H2O-containing atmosphere. Compared with their oxidation behaviour in air + H2O, the phenomenon was significantly enhanced in the atmosphere that coupled water vapour with a low oxygen pressure. Consequently, the Al-containing alloys should not be pre-oxidized in a water vapour atmosphere prior to long exposure to a corrosive atmosphere. In contrast, the chromia-forming Al-free 696 alloy exhibited identical oxidation behaviour in both atmospheres, demonstrating that the degradation of this alloy was not significantly affected by water vapour.

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 (O 2 ) has been demonstrated in the present paper. While at 800 °C and a p (O 2 ) of 10 −14 atm, a single n -chromia is observed, at 900 °C and a p (O 2 ) of 10 −12 atm, a duplex n - and p -chromia is obtained. Between these two situations, a stoichiometric chromia exhibiting insulating properties could be identified at 850 °C and a p (O 2 ) of 10 −13 atm. In every case, the morphology of the oxide scale is duplex and seems to depend only on the growth direction: equiaxis grains for an inward (anionic) growth and columnar grains for an outward (cationic) growth. The nature of point defects, linked to the n or p semiconducting character, governs the oxide growth but surprisingly, does not seem to have any influence on the oxide scale morphology. Finally, the control of the growth of an insulating stoichiometric chromia layer should permit to optimize its protective character.

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 and Rietveld refinement in order to describe this phase as a pseudolamellar structure comparable to the one of Ti4Ni4Si7. Results evidenced that diffusion in solid state governs the oxidation rate of these silicides. Ti4Ni4Si7 oxidation rate was assessed as being one order of magnitude lower than the one of Ti3(Ni,Cr)3CrSi6, while this latter readily transformed into Ti4Ni4Si7 during the first time of oxidation. The understanding of this particular behaviour in which the oxidation rate of Ti3(Ni,Cr)3CrSi6 was not affected by the phase transformation implied to consider the crystallographic lamellar features of these compounds that play a major role in the diffusion of the most oxidizable elements.

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 MgF 2 as the transport agent and pure silicon (high activity) as the master alloy. Coated pure vanadium and coated V-4Cr-4Ti alloy were studied and compared as substrates. In both cases, the growth of the silicide layers (V 3 Si, V 5 Si 3 , V 6 Si 5 and VSi 2 ) was controlled exclusively by solid-state diffusion, and the growth kinetics followed a parabolic law. Wagner's analysis was adopted to calculate the integrated diffusion coefficients for all silicides. The estimated values of the integrated diffusion coefficients range from approximately 10 −9 to 10 −13 cm 2 s −1 . Then, a diffusion-based numerical approach was used to evaluate the growth and consumption of the layers when the coated substrates were exposed at critical temperatures. The estimated lifetimes of the upper VSi 2 layer were 400 h and 280 h for pure vanadium and the V-4Cr-4Ti alloy, respectively. The result from the numeric simulation was in good agreement with the layer thicknesses measured after aging the coated samples at 1150 °C under vacuum.

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, combined with calculations based on the density functional theory. Experimentally, the transition metal positions are determined using the anomalous scattering effect close to the energy absorption threshold. First principles calculations carried out on the as-determined structures show that the preferential site occupations are explained by thermodynamic arguments. Theoretical calculations highlight the influence of Cr atoms on the lattice parameters, and reveal that the experimental Cr content corresponds to the amount required to reach the equilibrium between X3T2(T1-xCrx)2Si6 and X4T4Si7.

Fine equiaxed grain regions are frequently observed in additively manufactured Inconel 718 alloy. Based on a grain-to-grain orientation analysis using EBSD, many assemblies of neighboring grains in these regions have been found to display multiple-twins orientation relationships sharing common 〈 110 〉 directions and exhibiting 5-fold symmetry. This is an experimental proof that the grain refinement observed in inconel 718 is due to Icosahedral Short-Range Order (ISRO) mediated nucleation mechanism. This is the first report of ISRO-mediated nucleation of fcc nickel which widens the perspectives on the microstructures control in additive manufacturing of Ni-based superalloys.

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 used as bond coat. The ceramic topcoats were manufactured by electron-beam physical vapour deposition (YSZ and GZO) and magnetron sputtering (Y2SiO5).The different E/TBC systems were tested under cyclic oxidation conditions in air at 1100 and 1200°C. Lifetimes exceeding 1000 cycles of 1h dwell time at 1100°C were determined. The YSZ, GZO and combined Y2SiO5+GZO topcoats did not spall off during the maximum exposure time, exhibiting good adherence to the thermally grown oxide scale which consisted of mixed oxides of Fe,Ti, Cr and Nb embedded in silica. For the E/TBC systems with YSZ and GZO which were thermally cycled at 1200°C, lifetimes up to 850 cycles were measured; that of the system with a combined Y2SiO5+GZO topcoat exceeded again 1000 cycles.

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 based alloy (Inconel 625) were exposed in air to three different synthetic ashes, with various chloride contents, including ZnCl2 at isothermal temperatures of 450 and 650 °C in a muffle furnace. After the test, thickness and mass losses were evaluated on two separate samples, and metallographic cross sections of the specimens were characterized via SEM/EDX analyses. Both measurement results were in good agreement and showed that the corrosion observed on both materials was higher in the presence of zinc chloride in ash at 450 °C than in ashes without heavy metal chloride at 650 °C.

International audience; 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 higher for the LBM material at 1050 °C. This high oxidation rate induced poor oxide scalecompactness, void formation in the subsurface region and the formation of a high amount of Nb1.5Cr0.5O4 at the alloy-oxide interface.

Oxidation of chromium at 800 °C for 30 min at oxygen activity from 5.10−14 atm to 5.10−13 atm have been conducted to grow an insulating chromia. Microstructural and semiconducting properties have been investigated using electron microscopy and photoelectrochemistry. The scales always exhibit a duplex microstructure with equiaxed and columnar grains, as well as a both n-type and insulating semiconduction type. Successive oxidation tests have demonstrated the higher protective nature of this chromia scale compared to the air grown one. Chromia semiconducting properties are finally described vs. oxygen activity in a large range of variation.

The oxidation behaviour of four model alloys with the composition Ni–25Cr–xMn (with x = 0, 0.5, 1 and 1.5 wt%) was investigated at 1050 °C in air by thermogravimetry and by in situ observations in an environmental scanning electron microscope (ESEM). The addition of manganese modifies the oxidation rate of Ni–25Cr alloys by (1) increasing the parabolic constant k p compared to that for Ni–25Cr and (2) lowering the short-time oxidation rate. Regardless of the Mn concentration, in situ ESEM observations indicated the formation of spinel crystallites from the very beginning of the oxidation process. The size of the spinel crystallites was directly linked to the initial Mn concentration. The obtained results suggested that the formation of the spinel layer at the top of the chromia oxide scale rather than at the metal–oxide interface as thermodynamically expected must be attributed to the higher diffusion rate of Mn than Cr both in the lattice and at the grain boundary.

International audience; 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 produced by pack cementation. The Co- and Fe-modified M7Si6-based layers also contained boron. On these grit blasted bond coats, ceramic topcoats of 7 wt.% yttria partially stabilised zirconia (YSZ) and gadolinium zirconate (GZO) were deposited using electron-beam physical vapour deposition. The E/TBC systems were thermally cycled at 1100 °C and 1200 °C in laboratory air (1 h at high temperature, 10 min at ambient temperature). Cross-sectional examinations of the samples after cyclic testing were carried out using scanning electron microscopy to study the protection capability of the E/TBC systems and failure mechanisms.The lifetimes of the E/TBC systems exceeded the maximum exposure period of 1000 cycles at 1100 °C. When cyclically tested at 1200 °C, the samples with Ni-modified and boron containing Co-modified M7Si6-based bond coats failed within 700 cycles. Failure was caused by spallation of thick oxides scales thermally grown on the substrate after degradation of the bond coats. The E/TBC systems with boron containing Fe-modified M7Si6-based bond coats exhibited lifetimes approaching 1000 cycles at 1200 °C. For both YSZ and GZO topcoats, chemical reactions with the TGOs were observed.

International audience; A thermal oxide scale has been grown on a high-chromium iron-nickel alloy under very low oxygen partial pressure (1050 degrees C, 10(-10) Pa). In this paper, a special attention has been paid to morphological and chemical characterizations of the scale by scanning transmission electron microscopy and energy dispersive X-ray analysis at high resolution on a cross-section thin lamella beforehand prepared by using a combined focused ion beam/scanning electron microscope instrument. The complexity of the oxide layer is highlighted, and the correlation between the present results and the ones of a photoelectrochemical study is discussed. (C) 2015 Elsevier Ltd. All rights reserved.

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.

International audience; 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 have been investigated using photoelectrochemistry (PEC). Classical characterizations show that chromia is the main oxidation product whatever maybe the oxygen activity. PEC reveals additionally the presence of (i) n-type Cr2O3 at p(O2) ~ 10−14 atm and (ii) both n-type and p-type Cr2O3 at higher oxygen pressures. The mechanisms of oxidation are discussed as a function of the major point defects that govern the oxide scale growth.

International audience; 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, M5Si3, MSi, M6Si5, MSi2 and (Si). Microstructural observations suggest two class II invariant transformations associated to the phases Liquid, M5Si3, MSi2 and MSi, and Liquid, M5Si3, MSi2 and M6Si5, respectively. The existence of a maximum on the monovariant line between Liquid, M5Si3 and MSi2 was evidenced.

International audience; The present work is focused on the oxidation at 1050 degrees C of a model chromia-forming alloy, paying special attention to the control of the oxygen partial pressure. Taking benefit of a recently developed approach to describe and fit photocurrent energy spectra, photoelectrochemical characterizations allowed to reveal the presence, in the scale formed at low P(O-2) (10(-15) atm), of an unexpected high number of oxide phases. This result underlines the complexity of the scale in term of chemical composition as well as of the semiconducting types of the individual phases.

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 confirmed. The solubilities of Cr in V6Si5 and of V in CrSi have been measured. A ternary phase (Cr,V)11Si8 was observed and its homogeneity range, which is at constant Si ratio, was determined at 1200 °C.

International audience; This paper reports the effects of adding from 2 to 8 at.% tin on the oxidation behaviour of Nb/Nb5Si3 composites at 815 degrees C and at higher temperatures (1100 and 1200 degrees 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 induces the accumulation of tin at the oxide/internal oxidation zone boundary. Low melting point phases (NbSn2 and/or pure Sn) form at 815 degrees C, whereas a layer of M5Si3 and Nb5SiSn2 forms at 1100 and 1200 degrees C. Once these products are formed, they generate an oxygen diffusion barrier and allow the elimination of pesting. However, for long oxidation processes at 1100 degrees C, the oxidation rate of Nb/Nb5Si3 composites containing tin should be higher than that for tin-free composites. Moreover, some oxidation results have suggested that the presence of A15-(Nb,Ti)(3)(Sn,Ti) in the microstructure of composites with at.%Sn > 2 can severely impact the low temperature fracture toughness of these composites.

International audience; Chromia grown on pure chromium at 900 A degrees C for 30 min at an oxygen partial pressure p(O-2) 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 (similar to 650 nm thick) and p-chromia with columnar morphology in the external part (similar to 900 nm thick). Grain orientation maps also revealed the presence of a c-oriented chromia layer at the interface between the n- and the p-subscales. This aOE (c) 0001 > textured layer was identified as the first-grown chromia layer. It means that internal n-equiaxis chromia grew by anionic transport governed by oxygen vacancy diffusion, whereas external p-columnar chromia layer grew outwards and was controlled by chromium vacancy diffusion.

International audience; 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 coatings with purified Na was evaluated at 550 A degrees C for exposure times up to 4250 h. All coatings evidenced high chemical stability in Na even though Na penetration and slow coating dissolution could be evidenced. The penetration depth of Na was observed to depend on the coating nature induced by the deposition process.

International audience; 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-pm-thick oxide scale of Cr2O3 or Al2O3. The lifetime of Ni-30Cr depended on the competition between the oxide growth and its dissolution in the melt. For Ni-8Al-28Cr, the high solubility of alumina in the melt studied here led to severe aluminium loss in a few minutes and clearly demonstrated the higher efficiency of chromia-forming alloys for molten glass applications.

The halide-activated pack-cementation technique was employed to fabricate a diffusion coating that is resistant both to isothermal and to cyclic oxidation in air at 650 °C on the surface of the V–4Cr–4Ti vanadium alloy that is a potential core component of future nuclear systems. A thermodynamic assessment determined the deposit conditions in terms of master alloy, activator, filler and temperature. The partial pressures of the main gaseous species (SiCl4, SiCl2 and VCl2) in the pack were calculated with the master alloy Si and the mixture VSi2 + Si. The VSi2 + Si master alloy was used to limit vanadium loss from the surface. The obtained coating consisted of multi-layered VxSiy silicides with an outer layer of VSi2. This silicide developed a protective layer of silica at 650 °C in air and was not susceptible to the pest phenomenon, unlike other refractory silicides (MoSi2, NbSi2). We suggest that VSi2 exhibits no risk of rapid degradation in the gas fast reactor (GFR) conditions.

International audience; 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.

This work focuses on the effect of tin additions (2, 5 and 8%) to the MASC alloy (Nb-25Ti-8Hf-2Cr-2Al-18Si) on the microstructure and the oxidation behaviour at 815°C in air. The alloys are mainly constituted of a niobium solid solution plus the () Nb5Si3 silicides. For the higher Sn additions (5 and 8%), a fourth phase is evidenced: it is enriched in Sn and has a crystal structure close to Nb3Sn. The oxidation resistance of these alloys is clearly improved by tin additions: the oxygen inward diffusion is hindered and consequently the fragmentation of the silicides is avoided. Cracks in silicides are no longer observed for the MASC containing 8%Sn. This effect is not attributed to a better efficiency of the oxide scales but rather to the reduction of the niobium solid solution fraction with tin additions.

Austenitic nickel-iron-chromium based superalloys are materials of choice for high temperature applications as they provide high temperature creep resistance associated with a suitable oxidation behavior in the temperature range of 600-1100°C. However, these properties are not sufficient for applications as Steam Methane Reformer (SMR). As a consequence, aluminum and chromium coatings are developed by the pack-cementation technique to improve their corrosion resistance. The oxidation behavior of the coated samples has been carried out in air at 1050°C. Chromium deposition leads to a layer of bcc chromium-iron solid solution. Oxidation tests indicated that a too high chromium concentration induces a too rapid growth of the chromia layer. In the case of aluminum coatings, a layer of -NiAl is formed at the surface of the alloy. It permits a significant decrease of the oxidation rate.

The feasibility of surface chromium enrichment by pack-cementation was assessed for different low chromium-containing cobalt alloys, in order to improve their resistance against high temperature. A binary Co-10Cr alloy, two ternary Co-10Cr-0.5C and Co-10Cr-1.0C alloys and two TaC-containing Co-10Cr-based alloys were elaborated by foundry for the study. 7.5h-long and 15h-long cementations at 1050°C, followed or not by a 75h-long heat treatment at 1200°C were performed on these alloys. Microstructure examinations performed using a Scanning Electron Microscope and concentration profiles using Electron Probe Micro Analysis-Wavelength Dispersion Spectrometry were realized in order to analyze the level of Cr-enrichment of the sub-surface region, with as studied criteria: the nature of the external Cr-enriched zone, the maximal chromium content on surface and the depth of chromium enrichment. The Cr-enrichment of the sub-surface succeeded for the Co-10Cr alloy and for the two tantalum-containing alloys, with the formation of an external metallic zone containing around 30wt.%Cr. In contrast the chromium carbides-containing alloys were effectively enriched in chromium in surface but in the form of a continuous chromium carbide layer which can induce other problems such as spallation and then possible fast oxidation of the denuded alloy. Finally it appeared that only the carbon-free alloys, and the alloys reinforced by carbides more stable than chromium carbides, are potentially able to be successful enriched in chromium in their sub-surface by pack-cementation.

Samples of MoSi 2 were synthesised by arc melting and uniaxial hot pressing from different starting materials in order to distinguish the effects of sample preparations on the occurrence of the pest phenomenon, i.e. the rapid fragmentation of the pieces. The arc-melted samples presented cracks and porosities after preparation whereas the hot pressed samples were well densified (>95%). The pest appeared after no more than a few hours of exposure in air at 500 °C for arc-melted samples, whereas the sintered MoSi 2 samples with our experimental conditions were not at all affected. The corrosion products consisted of stoichiometric MoO 3 and SiO 2 mixtures. Both isothermal and cyclic oxidation measurements over long durations (>2000 h) support these results. It appears that the oxidation kinetics of hot pressed samples are governed by surface or phase boundary reactions and consequently depends on the grain size and the distribution of the initial SiO 2 particles, i.e. on the MoSi 2 microstructure.

Background & Aims Little is known about the magnitude of the risk of anal and rectal cancer in patients with anal and/or perineal Crohn's disease. We aimed to assess the risk of anal and rectal cancer in patients with Crohn's perianal disease followed up in the Cancers Et Surrisque Associe aux Maladies Inflammatoires Intestinales En France (CESAME) cohort. Methods We collected data from 19,486 patients with inflammatory bowel disease (IBD) enrolled in the observational CESAME study in France, from May 2004 through June 2005; 14.9% of participants had past or current anal and/or perianal Crohn's disease. Subjects were followed up for a median time of 35 months (interquartile range, 29–40 mo). To identify risk factors for anal cancer in the total CESAME population, we performed a case-control study in which participants were matched for age and sex. Results Among the total IBD population, 8 patients developed anal cancer and 14 patients developed rectal cancer. In the subgroup of 2911 patients with past or current anal and/or perianal Crohn's lesions at cohort entry, 2 developed anal squamous-cell carcinoma, 3 developed perianal fistula–related adenocarcinoma, and 6 developed rectal cancer. The corresponding incidence rates were 0.26 per 1000 patient-years for anal squamous-cell carcinoma, 0.38 per 1000 patient-years for perianal fistula–related adenocarcinoma, and 0.77 per 1000 patient-years for rectal cancer. Among the 16,575 patients with ulcerative colitis or Crohn's disease without anal or perianal lesions, the incidence rate of anal cancer was 0.08 per 1000 patient-years and of rectal cancer was 0.21 per 1000 patient-years. Among factors tested by univariate conditional regression (IBD subtype, disease duration, exposure to immune-suppressive therapy, presence of past or current anal and/or perianal lesions), the presence of past or current anal and/or perianal lesions at cohort entry was the only factor significantly associated with development of anal cancer (odds ratio, 11.2; 95% CI, 1.18-551.51; P = .03). Conclusions In an analysis of data from the CESAME cohort in France, patients with anal and/or perianal Crohn's disease have a high risk of anal cancer, including perianal fistula–related cancer, and a high risk of rectal cancer.

Chromium can be a candidate of interest as a base component for refractory alloys for high temperature applications. Few data are available about oxidation kinetic of chromium in air for temperature as high as 1300 °C. Moreover, rare papers take the nitridation of chromium into account in the description of the oxidation process or in the calculation of the kinetic constants. In the present study, global methods like thermogravimetry were linked to thickness measurements and microstructural characterisation to evaluate oxidation and nitridation contribution to weight gain. High stress levels were induced in the oxide layer during its formation. The kinetic constant associated to the nitridation, at this temperature, was one order of magnitude higher than the parabolic oxidation constant. Experiments demonstrated that the presence of nitrogen in the substrate is always a precursor to breakdown of the oxide layer and does not result from diffusion through the Cr2O3 layer.

In this study, chromium based alloys containing a hardening NiAl phase are investigated from 1100°C to 1300°C in air. The influence of the NiAl content and of the Al/Ni ratio on microstructure modification and on oxidation behaviour are characterized by metallography and thermogravimetry. Increasing the Al/Ni ratio leads to a higher Al content in the chromium solid solution but does not modify the amount of primary NiAl. At high temperature, and for NiAl content exceeding 16 at%, a duplex oxide layer forms at the surface of the alloys exposed in air, alumina in the inner part, and chromia in the outer part. The oxidation behavior is discussed according to oxidation profile and to the thermodynamic predominance diagram of the involved species.

The oxidation and nitridation of pure chromium and of chromium alloys containing 0.5 to 5at% silicon was investigated at 1300°C in several atmospheres. Global methods like thermogravimetry were associated to thickness measurements and microstructural characterisation to evaluate oxidation mechanisms. The contribution of nitridation to weight gain during high temperature exposure is discussed, examining nitride volume fraction. Experiments demonstrate that the presence of nitrogen in the substrate is always consecutive to a breakdown of the oxide layer and does not result from diffusion through the Cr2O3 layer. Silicon, when present in chromium solid solution, slows down the oxidation kinetics and limits the progression of nitrogen in the chromium lattice and at grain boundaries. The absence of the Cr2N layer beneath the metal/oxide interface does not benefit to the adherence of the oxide scale. Oxidation of silicon in chromium leads to the formation of discontinuous particles of SiO2 at the metal/oxide interface, at the grain boundaries and dispersed in the bulk in the alloy sub-surface.

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 into account data from existing assessment of binary sub-systems. Four intermediate phases were considered as stoichiometric compounds (Cr,V) x (Si) y with substitution of Cr and V at Si ratio constant: (Cr,V)Si, (Cr,V) 5 Si 3 , (Cr,V) 11 Si 8 and (Cr,V) 6 Si 5 . Two others phases (Cr,V)Si 2 and (Cr,V) 3 Si presenting a slight domain of homogeneity, were described as (Cr,Si,V) 1 (Cr,Si) 2 and (Cr,Si,V) 3 (Cr,Si,V) 1 respectively. The metallic liquid phase and the terminal solid solutions of chromium and vanadium were described by the disordered solutions model as (Cr,Si,V) 1 (Va) 3 . The silicon admitting any solubility, its description was limited to (Si). The resulting thermodynamic optimization led to a good agreement with experimental data.