Dépouillements

Oxide growth stress measurements and relaxation mechanisms for alumina scales grown on FeCrAlY / P. F. Tortorelli in Materials and corrosion, Vol. 63 N° 10 (Octobre 2012) 

Public ISBD [article]  in Materials and corrosion > Vol. 63 N° 10 (Octobre 2012) . - pp. 857–861 Titre : Oxide growth stress measurements and relaxation mechanisms for alumina scales grown on FeCrAlY Type de document : texte imprimé Auteurs : P. F. Tortorelli, Auteur ; E. D. Specht, Auteur ; K. L. More, Auteur Année de publication : 2013 Article en page(s) : pp. 857–861 Note générale : Génie mécanique Langues : Anglais (eng) Mots-clés : FeCrAlY;  high  temperature  oxidation;  oxide  growth  stress Résumé : Early-stage tensile stress evolution in α-Al2O3 scales during oxidation of FeCrAlY at 1000, 1050, 1100, and 1200 °C was monitored in situ by use of synchrotron radiation. Tensile stress development as a function of oxidation temperature indicated a dynamic interplay between stress generation and relaxation. An analysis of the time dependence of the data indicated that the observed relaxation of the initial tensile stress in the oxide scales at 1100 and 1200 °C is dominated by creep in the α-Al2O3. A thin layer of a (Fe,Cr,Al) oxide was observed at the oxide-gas interface, consistent with a mechanism whereby the conversion of (Fe,Cr,Al)2O3 to α-Al2O3 produces an initial tensile stress in the alumina scale. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201206760/abstract [article] Oxide growth stress measurements and relaxation mechanisms for alumina scales grown on FeCrAlY [texte imprimé] / P. F. Tortorelli, Auteur ; E. D. Specht, Auteur ; K. L. More, Auteur . - 2013 . - pp. 857–861. Génie mécanique Langues : Anglais (eng) in Materials and corrosion > Vol. 63 N° 10 (Octobre 2012) . - pp. 857–861 Mots-clés : FeCrAlY;  high  temperature  oxidation;  oxide  growth  stress Résumé : Early-stage tensile stress evolution in α-Al2O3 scales during oxidation of FeCrAlY at 1000, 1050, 1100, and 1200 °C was monitored in situ by use of synchrotron radiation. Tensile stress development as a function of oxidation temperature indicated a dynamic interplay between stress generation and relaxation. An analysis of the time dependence of the data indicated that the observed relaxation of the initial tensile stress in the oxide scales at 1100 and 1200 °C is dominated by creep in the α-Al2O3. A thin layer of a (Fe,Cr,Al) oxide was observed at the oxide-gas interface, consistent with a mechanism whereby the conversion of (Fe,Cr,Al)2O3 to α-Al2O3 produces an initial tensile stress in the alumina scale. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201206760/abstract

Effect of Fe and partial pressure of oxygen on the formation and phase transformation behavior of Al2O3 scale / S. Hayashi in Materials and corrosion, Vol. 63 N° 10 (Octobre 2012) 

Public ISBD [article]  in Materials and corrosion > Vol. 63 N° 10 (Octobre 2012) . - pp. 862–868 Titre : Effect of Fe and partial pressure of oxygen on the formation and phase transformation behavior of Al2O3 scale Type de document : texte imprimé Auteurs : S. Hayashi, Auteur ; Y. Takada, Auteur ; I. Saeki, Auteur Année de publication : 2013 Article en page(s) : pp. 862–868 Note générale : Génie mécanique Langues : Anglais (eng) Résumé : The effect of oxygen partial pressure on the phase transformation of Al2O3 scale on various Fe–Al alloys with and without very thin (∼100 nm) Fe coating was investigated. Fe-coating on Fe–Al alloys can effectively suppress metastable Al2O3 formation, but little effect was observed when the samples were oxidized in a low partial pressure of oxygen. Under the low equation image atmosphere, metastable to stable α-Al2O3 scale phase transformation on both Fe-coated and non-coated Fe–Al alloys was significantly delayed. The lattice spacing of α-Al2O3 scale formed in air decreased with increasing alloy Al content. Further decrease in the lattice spacing of α-Al2O3 scale was observed when the alloy was oxidized in low equation image. The results obtained clearly indicated that the formation of Fe2O3 or Fe3+ in metastable Al2O3 accelerated the metastable to stable α-Al2O3 scale transformation. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201206731/abstract [article] Effect of Fe and partial pressure of oxygen on the formation and phase transformation behavior of Al2O3 scale [texte imprimé] / S. Hayashi, Auteur ; Y. Takada, Auteur ; I. Saeki, Auteur . - 2013 . - pp. 862–868. Génie mécanique Langues : Anglais (eng) in Materials and corrosion > Vol. 63 N° 10 (Octobre 2012) . - pp. 862–868 Résumé : The effect of oxygen partial pressure on the phase transformation of Al2O3 scale on various Fe–Al alloys with and without very thin (∼100 nm) Fe coating was investigated. Fe-coating on Fe–Al alloys can effectively suppress metastable Al2O3 formation, but little effect was observed when the samples were oxidized in a low partial pressure of oxygen. Under the low equation image atmosphere, metastable to stable α-Al2O3 scale phase transformation on both Fe-coated and non-coated Fe–Al alloys was significantly delayed. The lattice spacing of α-Al2O3 scale formed in air decreased with increasing alloy Al content. Further decrease in the lattice spacing of α-Al2O3 scale was observed when the alloy was oxidized in low equation image. The results obtained clearly indicated that the formation of Fe2O3 or Fe3+ in metastable Al2O3 accelerated the metastable to stable α-Al2O3 scale transformation. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201206731/abstract

Effects of water vapour and oxygen partial pressures on low carbon steel oxidation in N2–H2–H2O mixtures / H. Yin in Materials and corrosion, Vol. 63 N° 10 (Octobre 2012) 

Public ISBD [article]  in Materials and corrosion > Vol. 63 N° 10 (Octobre 2012) . - pp. 869–877 Titre : Effects of water vapour and oxygen partial pressures on low carbon steel oxidation in N2–H2–H2O mixtures Type de document : texte imprimé Auteurs : H. Yin, Auteur ; W. Y. D. Yuen, Auteur ; D. J. Young, Auteur Année de publication : 2013 Article en page(s) : pp. 869–877 Note générale : Génie mécanique Langues : Anglais (eng) Mots-clés : High  temperature  oxidation;  hydroxyl;  low  carbon  steel;  water  vapour  effect Résumé : A low carbon, low silicon steel was oxidised at temperatures of 900–1000 °C in flowing N2–H2–H2O gas mixtures in which oxygen and water vapour partial pressures were varied independently. Scales of dense, single-phase, coarse grained wüstite grew rapidly, according to parabolic kinetics. Both the scaling rate and the oxide grain growth increased with PO2 at constant PH2O and also with equation image at constant PO2. An inert marker experiment showed that significant oxygen transport but majority metal transport supported scale growth. Gas composition effects are interpreted using point defect models involving formation of hydroxyl species on anion sites as well as cation vacancies. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201206570/abstract [article] Effects of water vapour and oxygen partial pressures on low carbon steel oxidation in N2–H2–H2O mixtures [texte imprimé] / H. Yin, Auteur ; W. Y. D. Yuen, Auteur ; D. J. Young, Auteur . - 2013 . - pp. 869–877. Génie mécanique Langues : Anglais (eng) in Materials and corrosion > Vol. 63 N° 10 (Octobre 2012) . - pp. 869–877 Mots-clés : High  temperature  oxidation;  hydroxyl;  low  carbon  steel;  water  vapour  effect Résumé : A low carbon, low silicon steel was oxidised at temperatures of 900–1000 °C in flowing N2–H2–H2O gas mixtures in which oxygen and water vapour partial pressures were varied independently. Scales of dense, single-phase, coarse grained wüstite grew rapidly, according to parabolic kinetics. Both the scaling rate and the oxide grain growth increased with PO2 at constant PH2O and also with equation image at constant PO2. An inert marker experiment showed that significant oxygen transport but majority metal transport supported scale growth. Gas composition effects are interpreted using point defect models involving formation of hydroxyl species on anion sites as well as cation vacancies. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201206570/abstract

Oxide scale formation and subsurface phase transformations during long-term steam exposure of the cobalt base alloy 25 / L. García Fresnillo in Materials and corrosion, Vol. 63 N° 10 (Octobre 2012) 

Public ISBD [article]  in Materials and corrosion > Vol. 63 N° 10 (Octobre 2012) . - pp. 878–888 Titre : Oxide scale formation and subsurface phase transformations during long-term steam exposure of the cobalt base alloy 25 Type de document : texte imprimé Auteurs : L. García Fresnillo, Auteur ; A. Chyrkin, Auteur ; T. Hüttel, Auteur Année de publication : 2013 Article en page(s) : pp. 878–888 Note générale : Génie mécanique Langues : Anglais (eng) Mots-clés : Chromium  depletion;  cobalt  base  alloys;  precipitate  enrichment;  steam  oxidation Résumé : High chromium nickel and cobalt base alloys are presently being considered as construction materials for various components in high efficiency steam turbines with envisaged operating temperatures around 700 °C. In the present study, the steam oxidation behavior of the cobalt base alloy 25 in the temperature range 650–800 °C was investigated whereby exposures up to 10 000 were carried out. Post exposure analyses of the oxidation products and alloy microstructures included optical microscopy, scanning and transmission electron microscopy, X-ray diffraction analysis and secondary neutrals mass spectrometry. The experiments showed in all cases formation of oxide scales mainly consisting of chromia with minor amounts of outer Cr/Mn spinel and internal silica. The oxidation induced chromium depletion resulted in a number of microstructural changes in the subsurface depletion layer. First, the intermetallic phase Co3W became enriched at the scale alloy interface. Additionally, the chromium rich M23C6 and the tungsten rich M6C dissolved in the depletion layer. The mechanisms for occurrence of these effects are discussed on the basis of phase equilibria in the binary Co–W and the ternary Co–Cr–W system. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201206683/abstract [article] Oxide scale formation and subsurface phase transformations during long-term steam exposure of the cobalt base alloy 25 [texte imprimé] / L. García Fresnillo, Auteur ; A. Chyrkin, Auteur ; T. Hüttel, Auteur . - 2013 . - pp. 878–888. Génie mécanique Langues : Anglais (eng) in Materials and corrosion > Vol. 63 N° 10 (Octobre 2012) . - pp. 878–888 Mots-clés : Chromium  depletion;  cobalt  base  alloys;  precipitate  enrichment;  steam  oxidation Résumé : High chromium nickel and cobalt base alloys are presently being considered as construction materials for various components in high efficiency steam turbines with envisaged operating temperatures around 700 °C. In the present study, the steam oxidation behavior of the cobalt base alloy 25 in the temperature range 650–800 °C was investigated whereby exposures up to 10 000 were carried out. Post exposure analyses of the oxidation products and alloy microstructures included optical microscopy, scanning and transmission electron microscopy, X-ray diffraction analysis and secondary neutrals mass spectrometry. The experiments showed in all cases formation of oxide scales mainly consisting of chromia with minor amounts of outer Cr/Mn spinel and internal silica. The oxidation induced chromium depletion resulted in a number of microstructural changes in the subsurface depletion layer. First, the intermetallic phase Co3W became enriched at the scale alloy interface. Additionally, the chromium rich M23C6 and the tungsten rich M6C dissolved in the depletion layer. The mechanisms for occurrence of these effects are discussed on the basis of phase equilibria in the binary Co–W and the ternary Co–Cr–W system. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201206683/abstract

Effect of exposure in steam or argon on the creep properties of Ni-based alloys / S. Dryepondt in Materials and corrosion, Vol. 63 N° 10 (Octobre 2012) 

Public ISBD [article]  in Materials and corrosion > Vol. 63 N° 10 (Octobre 2012) . - pp. 889–895 Titre : Effect of exposure in steam or argon on the creep properties of Ni-based alloys Type de document : texte imprimé Auteurs : S. Dryepondt, Auteur ; K. A. Unocic, Auteur ; B. A. Pint, Auteur Année de publication : 2013 Article en page(s) : pp. 889–895 Note générale : Génie mécanique Langues : Anglais (eng) Mots-clés : Creep;  gamma  prime  precipitates;  Ni  based  superalloys;  oxidation;  steam Résumé : Although expensive, Ni-based superalloys are of interest for the ultrasupercritical steam program because of their good creep and oxidation resistance at temperatures above 700 °C. As the effect of steam oxidation on the alloy mechanical properties is unknown, creep specimens of alloy CCA617, 740, and 230 were pre-oxidized for 2000 and 4000 h in steam at 800 °C before testing in air at the same temperature. Compared with as fabricated material, exposure in steam decreased the creep properties of alloy CCA617, had less of an effect on alloy 740, and did not affect alloy 230. Testing of a specimen repolished after steam exposure as well as microstructural observations indicate that the oxidation affected zone at the specimen surface is not responsible for the properties degradation. Surprisingly, a similar time anneal in an inert environment resulted in a drastic decrease of creep rupture life and an increase in the creep rate and elongation at rupture. Transmission electron microscopy analysis revealed that the mechanical properties decrease for alloy CCA617 is related to the absence of γ′ precipitates within the grains. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201206694/abstract [article] Effect of exposure in steam or argon on the creep properties of Ni-based alloys [texte imprimé] / S. Dryepondt, Auteur ; K. A. Unocic, Auteur ; B. A. Pint, Auteur . - 2013 . - pp. 889–895. Génie mécanique Langues : Anglais (eng) in Materials and corrosion > Vol. 63 N° 10 (Octobre 2012) . - pp. 889–895 Mots-clés : Creep;  gamma  prime  precipitates;  Ni  based  superalloys;  oxidation;  steam Résumé : Although expensive, Ni-based superalloys are of interest for the ultrasupercritical steam program because of their good creep and oxidation resistance at temperatures above 700 °C. As the effect of steam oxidation on the alloy mechanical properties is unknown, creep specimens of alloy CCA617, 740, and 230 were pre-oxidized for 2000 and 4000 h in steam at 800 °C before testing in air at the same temperature. Compared with as fabricated material, exposure in steam decreased the creep properties of alloy CCA617, had less of an effect on alloy 740, and did not affect alloy 230. Testing of a specimen repolished after steam exposure as well as microstructural observations indicate that the oxidation affected zone at the specimen surface is not responsible for the properties degradation. Surprisingly, a similar time anneal in an inert environment resulted in a drastic decrease of creep rupture life and an increase in the creep rate and elongation at rupture. Transmission electron microscopy analysis revealed that the mechanical properties decrease for alloy CCA617 is related to the absence of γ′ precipitates within the grains. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201206694/abstract

Oxide scale exfoliation and regrowth in TP347H superheater tubes / A. S. Sabau in Materials and corrosion, Vol. 63 N° 10 (Octobre 2012) 

Public ISBD [article]  in Materials and corrosion > Vol. 63 N° 10 (Octobre 2012) . - pp. 896–908 Titre : Oxide scale exfoliation and regrowth in TP347H superheater tubes Type de document : texte imprimé Auteurs : A. S. Sabau, Auteur ; I. G. Wright, Auteur ; J. P. Shingledecker, Auteur Année de publication : 2013 Article en page(s) : pp. 896–908 Note générale : Génie mécanique Langues : Anglais (eng) Résumé : This paper provides an introduction to a comprehensive model being developed to predict and control oxide scale exfoliation from the steam-side of superheater and reheater tubes in steam boilers. The model deals with the main phenomena involved in scale growth and failure in steam, and incorporates major variables related to boiler design and operation. The considerations used to calculate oxide growth under the specific constrains of small diameter tubes carrying high-pressure steam and operating with large temperature gradients under temperature and pressure cycling conditions, as well as the evolution of stresses and strains in the scales, are indicated but only a cursory description is given of the details of the analytical treatments. An example is presented of calculations made with the model to predict the extent of blockage expected in a single superheater loop as a function of time and outlet steam temperature under several realistic service conditions. The results suggest that problems due to scale exfoliation would be expected early in the operating life of superheater tubes made from austenitic steel TP347H. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201206640/abstract [article] Oxide scale exfoliation and regrowth in TP347H superheater tubes [texte imprimé] / A. S. Sabau, Auteur ; I. G. Wright, Auteur ; J. P. Shingledecker, Auteur . - 2013 . - pp. 896–908. Génie mécanique Langues : Anglais (eng) in Materials and corrosion > Vol. 63 N° 10 (Octobre 2012) . - pp. 896–908 Résumé : This paper provides an introduction to a comprehensive model being developed to predict and control oxide scale exfoliation from the steam-side of superheater and reheater tubes in steam boilers. The model deals with the main phenomena involved in scale growth and failure in steam, and incorporates major variables related to boiler design and operation. The considerations used to calculate oxide growth under the specific constrains of small diameter tubes carrying high-pressure steam and operating with large temperature gradients under temperature and pressure cycling conditions, as well as the evolution of stresses and strains in the scales, are indicated but only a cursory description is given of the details of the analytical treatments. An example is presented of calculations made with the model to predict the extent of blockage expected in a single superheater loop as a function of time and outlet steam temperature under several realistic service conditions. The results suggest that problems due to scale exfoliation would be expected early in the operating life of superheater tubes made from austenitic steel TP347H. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201206640/abstract

Interdiffusion behavior of Al-rich oxidation resistant coatings on ferritic–martensitic alloys / S. Velraj in Materials and corrosion, Vol. 63 N° 10 (Octobre 2012) 

Public ISBD [article]  in Materials and corrosion > Vol. 63 N° 10 (Octobre 2012) . - pp. 909–920 Titre : Interdiffusion behavior of Al-rich oxidation resistant coatings on ferritic–martensitic alloys Type de document : texte imprimé Auteurs : S. Velraj, Auteur ; Y. Zhang, Auteur ; E. W. Hawkins, Auteur Année de publication : 2013 Article en page(s) : pp. 909–920 Note générale : Génie mécanique Langues : Anglais (eng) Mots-clés : Al-rich  coatings;  aluminide  coatings;  chemical  vapor  deposition;  COSIM;  diffusion;  ferritic–martensitic  alloy;  oxidation;  pack  cementation;  water  vapor Résumé : Interdiffusion of thin Al-rich coatings synthesized by chemical vapor deposition (CVD) and pack cementation on 9Cr ferritic–martensitic alloys was investigated in the temperature range of 650–700 °C. The compositional changes after long-term exposures in laboratory air and air + 10 vol% H2O were examined experimentally. Interdiffusion was modeled by a modified coating oxidation and substrate interdiffusion model (COSIM) program. The modification enabled the program to directly input the concentration profiles of the as-deposited coating determined by electron probe microanalysis (EPMA). Reasonable agreement was achieved between the simulated and experimental Al profiles after exposures. The model was also applied to predict coating lifetime at 650–700 °C based on a minimum Al content (Cb) required at the coating surface to re-form protective oxide scale. In addition to a Cb value established from the failure of a thin CVD coating at 700 °C, values reported for slurry aluminide coatings were also included in lifetime predictions. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201206641/abstract [article] Interdiffusion behavior of Al-rich oxidation resistant coatings on ferritic–martensitic alloys [texte imprimé] / S. Velraj, Auteur ; Y. Zhang, Auteur ; E. W. Hawkins, Auteur . - 2013 . - pp. 909–920. Génie mécanique Langues : Anglais (eng) in Materials and corrosion > Vol. 63 N° 10 (Octobre 2012) . - pp. 909–920 Mots-clés : Al-rich  coatings;  aluminide  coatings;  chemical  vapor  deposition;  COSIM;  diffusion;  ferritic–martensitic  alloy;  oxidation;  pack  cementation;  water  vapor Résumé : Interdiffusion of thin Al-rich coatings synthesized by chemical vapor deposition (CVD) and pack cementation on 9Cr ferritic–martensitic alloys was investigated in the temperature range of 650–700 °C. The compositional changes after long-term exposures in laboratory air and air + 10 vol% H2O were examined experimentally. Interdiffusion was modeled by a modified coating oxidation and substrate interdiffusion model (COSIM) program. The modification enabled the program to directly input the concentration profiles of the as-deposited coating determined by electron probe microanalysis (EPMA). Reasonable agreement was achieved between the simulated and experimental Al profiles after exposures. The model was also applied to predict coating lifetime at 650–700 °C based on a minimum Al content (Cb) required at the coating surface to re-form protective oxide scale. In addition to a Cb value established from the failure of a thin CVD coating at 700 °C, values reported for slurry aluminide coatings were also included in lifetime predictions. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201206641/abstract

Novel processing in inert atmosphere and in air to manufacture high-activity slurry aluminide coatings modified by Pt and Pt/Ir / M. C. Galetz in Materials and corrosion, Vol. 63 N° 10 (Octobre 2012) 

Public ISBD [article]  in Materials and corrosion > Vol. 63 N° 10 (Octobre 2012) . - pp. 921–928 Titre : Novel processing in inert atmosphere and in air to manufacture high-activity slurry aluminide coatings modified by Pt and Pt/Ir Type de document : texte imprimé Auteurs : M. C. Galetz, Auteur ; X. Montero, Auteur ; H. Murakami, Auteur Année de publication : 2013 Article en page(s) : pp. 921–928 Note générale : Génie mécanique Langues : Anglais (eng) Mots-clés : Air;  aluminide;  iridium;  platinum;  slurry Résumé : Slurry-derived coatings are an interesting alternative method to pack aluminization of nickel-base superalloys, which provide similar properties and protection at high temperatures. For highest performance, these aluminide coatings are modified by the addition of Pt or, as recent research suggests, with Pt/Ir. While the combination of Pt and Pt/Ir with an out-of-pack process is state of the art, slurry coatings are of special interest as a repair method for turbine blades. In this study, the microstructural evolution of slurry-derived coatings manufactured on CM 247 in inert atmosphere as well as in air was investigated. Layers of Ni, Pt, and Pt/Ir mixtures were electrodeposited. After annealing, a diffusion heat-treatment with a slurry containing aluminum or aluminum–silicon powder was applied on the samples. The addition of silicon is well known to be beneficial for hot corrosion environments. The reaction and interdiffusion behavior of aluminum/aluminum–silicon determines the microstructural evolution of the coatings. Depending on the initial electroplated layer on the surface, different microstructures can be obtained, such as the Pt/Ir-modified beta phase (Ni,Pt)Al or two-phase layers of PtAl2 and NiAl. Additionally, the reactivity between the elements at the surface and those from the slurry was shown to determine homogeneity and surface roughness of the diffusion coating, also depending on the atmosphere used during slurry aluminization. Finally, it was demonstrated that iridium has a high influence on the diffusion behavior and especially the distribution of platinum in the coatings. Such new coatings have the potential to overcome some disadvantages of conventionally manufactured high-activity aluminide coatings, as the combination of Pt/Ir-electroplating with the slurry process results in less detrimental substrate elements like molybdenum or tungsten close to the surface. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201206773/abstract [article] Novel processing in inert atmosphere and in air to manufacture high-activity slurry aluminide coatings modified by Pt and Pt/Ir [texte imprimé] / M. C. Galetz, Auteur ; X. Montero, Auteur ; H. Murakami, Auteur . - 2013 . - pp. 921–928. Génie mécanique Langues : Anglais (eng) in Materials and corrosion > Vol. 63 N° 10 (Octobre 2012) . - pp. 921–928 Mots-clés : Air;  aluminide;  iridium;  platinum;  slurry Résumé : Slurry-derived coatings are an interesting alternative method to pack aluminization of nickel-base superalloys, which provide similar properties and protection at high temperatures. For highest performance, these aluminide coatings are modified by the addition of Pt or, as recent research suggests, with Pt/Ir. While the combination of Pt and Pt/Ir with an out-of-pack process is state of the art, slurry coatings are of special interest as a repair method for turbine blades. In this study, the microstructural evolution of slurry-derived coatings manufactured on CM 247 in inert atmosphere as well as in air was investigated. Layers of Ni, Pt, and Pt/Ir mixtures were electrodeposited. After annealing, a diffusion heat-treatment with a slurry containing aluminum or aluminum–silicon powder was applied on the samples. The addition of silicon is well known to be beneficial for hot corrosion environments. The reaction and interdiffusion behavior of aluminum/aluminum–silicon determines the microstructural evolution of the coatings. Depending on the initial electroplated layer on the surface, different microstructures can be obtained, such as the Pt/Ir-modified beta phase (Ni,Pt)Al or two-phase layers of PtAl2 and NiAl. Additionally, the reactivity between the elements at the surface and those from the slurry was shown to determine homogeneity and surface roughness of the diffusion coating, also depending on the atmosphere used during slurry aluminization. Finally, it was demonstrated that iridium has a high influence on the diffusion behavior and especially the distribution of platinum in the coatings. Such new coatings have the potential to overcome some disadvantages of conventionally manufactured high-activity aluminide coatings, as the combination of Pt/Ir-electroplating with the slurry process results in less detrimental substrate elements like molybdenum or tungsten close to the surface. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201206773/abstract

Factors affecting the microstructural stability and durability of thermal barrier coatings fabricated by air plasma spraying / M. A. Helminiak in Materials and corrosion, Vol. 63 N° 10 (Octobre 2012) 

Public ISBD [article]  in Materials and corrosion > Vol. 63 N° 10 (Octobre 2012) . - pp. 929–939 Titre : Factors affecting the microstructural stability and durability of thermal barrier coatings fabricated by air plasma spraying Type de document : texte imprimé Auteurs : M. A. Helminiak, Auteur ; N. M. Yanar, Auteur ; F. S. Pettit, Auteur Année de publication : 2013 Article en page(s) : pp. 929–939 Note générale : Génie mécanique Langues : Anglais (eng) Mots-clés : APS;  durability;  EBPVD;  thickness;  TBC;  YSZ  purity Résumé : The high-temperature behavior of high-purity, low-density (HP-LD) air plasma sprayed (APS) thermal barrier coatings (TBCs) with NiCoCrAlY bond coats deposited by argon-shrouded plasma spraying is described. The high purity yttria-stabilized zirconia resulted in top coats which are highly resistant to sintering and transformation from the metastable tetragonal phase to the equilibrium mixture of monoclinic and cubic phases. The thermal conductivity of the as-processed TBC is low but increases during high temperature exposure even before densification occurs. The porous topcoat microstructure also resulted in good spallation resistance during thermal cycling. The actual failure mechanisms of the APS coatings were found to depend on topcoat thickness, topcoat density, and the thermal cycle frequency. The failure mechanisms are described and the durability of the HP-LD coatings is compared with that of state-of-the-art electron beam physical vapor deposition TBCs. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201206646/abstract [article] Factors affecting the microstructural stability and durability of thermal barrier coatings fabricated by air plasma spraying [texte imprimé] / M. A. Helminiak, Auteur ; N. M. Yanar, Auteur ; F. S. Pettit, Auteur . - 2013 . - pp. 929–939. Génie mécanique Langues : Anglais (eng) in Materials and corrosion > Vol. 63 N° 10 (Octobre 2012) . - pp. 929–939 Mots-clés : APS;  durability;  EBPVD;  thickness;  TBC;  YSZ  purity Résumé : The high-temperature behavior of high-purity, low-density (HP-LD) air plasma sprayed (APS) thermal barrier coatings (TBCs) with NiCoCrAlY bond coats deposited by argon-shrouded plasma spraying is described. The high purity yttria-stabilized zirconia resulted in top coats which are highly resistant to sintering and transformation from the metastable tetragonal phase to the equilibrium mixture of monoclinic and cubic phases. The thermal conductivity of the as-processed TBC is low but increases during high temperature exposure even before densification occurs. The porous topcoat microstructure also resulted in good spallation resistance during thermal cycling. The actual failure mechanisms of the APS coatings were found to depend on topcoat thickness, topcoat density, and the thermal cycle frequency. The failure mechanisms are described and the durability of the HP-LD coatings is compared with that of state-of-the-art electron beam physical vapor deposition TBCs. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201206646/abstract

Effect of nano-particulate sol–gel coatings on the oxidation resistance of high-strength steel alloys during the press-hardening process / M. Yekehtaz in Materials and corrosion, Vol. 63 N° 10 (Octobre 2012) 

Public ISBD [article]  in Materials and corrosion > Vol. 63 N° 10 (Octobre 2012) . - pp. 940–947 Titre : Effect of nano-particulate sol–gel coatings on the oxidation resistance of high-strength steel alloys during the press-hardening process Type de document : texte imprimé Auteurs : M. Yekehtaz, Auteur ; C. Klesen, Auteur ; S. Benfer, Auteur Année de publication : 2013 Article en page(s) : pp. 940–947 Note générale : Génie mécanique Langues : Anglais (eng) Mots-clés : High-strength  steel  alloys;  nanoparticle;  oxidation  protection;  press  hardening;  sol–gel  coatings Résumé : The need for lighter constructional materials in automotive industries has increased the use of high-strength steel alloys. To enhance passenger's safety press hardening may be applied to steel parts. However, as the steel parts are heated up to 950 °C during this process they have to be protected by some kind of coating against the intense oxide formation usually taking place. As the coating systems used so far all have certain disadvantages in this work the ability of nano-particulate thin coatings obtained by the sol–gel process to improve the oxidation resistance of 22MnB5 steel is investigated. The coatings obtained from three sols containing lithium aluminum silicate and potassium aluminum silicate showed the best performance against oxidation. The structural properties of the coating materials were characterized using different methods like XRD and differential thermal analysis. Comparison of the oxidation rate constants proved the ability of the coatings to protect against oxidation at temperatures up to 800 °C. Press-hardening experiments in combination with investigations on the thermal shock resistance of the coated samples also showed the ability of the coatings to stay intact during press hardening with only slight spalling of the coatings in the bending areas. The absence of any secondary intermetallic phases and layer residues during laser beam welding experiments on coated samples proves the suitability of the nano-particulate coatings for further industrial processing. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201206729/abstract [article] Effect of nano-particulate sol–gel coatings on the oxidation resistance of high-strength steel alloys during the press-hardening process [texte imprimé] / M. Yekehtaz, Auteur ; C. Klesen, Auteur ; S. Benfer, Auteur . - 2013 . - pp. 940–947. Génie mécanique Langues : Anglais (eng) in Materials and corrosion > Vol. 63 N° 10 (Octobre 2012) . - pp. 940–947 Mots-clés : High-strength  steel  alloys;  nanoparticle;  oxidation  protection;  press  hardening;  sol–gel  coatings Résumé : The need for lighter constructional materials in automotive industries has increased the use of high-strength steel alloys. To enhance passenger's safety press hardening may be applied to steel parts. However, as the steel parts are heated up to 950 °C during this process they have to be protected by some kind of coating against the intense oxide formation usually taking place. As the coating systems used so far all have certain disadvantages in this work the ability of nano-particulate thin coatings obtained by the sol–gel process to improve the oxidation resistance of 22MnB5 steel is investigated. The coatings obtained from three sols containing lithium aluminum silicate and potassium aluminum silicate showed the best performance against oxidation. The structural properties of the coating materials were characterized using different methods like XRD and differential thermal analysis. Comparison of the oxidation rate constants proved the ability of the coatings to protect against oxidation at temperatures up to 800 °C. Press-hardening experiments in combination with investigations on the thermal shock resistance of the coated samples also showed the ability of the coatings to stay intact during press hardening with only slight spalling of the coatings in the bending areas. The absence of any secondary intermetallic phases and layer residues during laser beam welding experiments on coated samples proves the suitability of the nano-particulate coatings for further industrial processing. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201206729/abstract

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