Documents disponibles écrits par cet auteur

Effect of water vapour on cyclic oxidation of Fe–Cr alloys / N. K. Othman in Materials and corrosion, Vol. 62 N° 6 (Juin 2011) 

Public ISBD [article]  in Materials and corrosion > Vol. 62 N° 6 (Juin 2011) . - pp. 496–503 Titre : Effect of water vapour on cyclic oxidation of Fe–Cr alloys Type de document : texte imprimé Auteurs : N. K. Othman, Auteur ; J. Zhang, Auteur ; D. J. Young, Auteur Année de publication : 2011 Article en page(s) : pp. 496–503 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Alloy  depletion  Breakaway  Cyclic  oxidation Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Model Fe–Cr alloys containing 9, 17 or 25 wt% Cr were subjected to repeated 1 h cycles of exposure at 700 °C to flowing gas mixtures of Ar-20O2, Ar-20O2-5H2O and Ar-5O2-20H2O (all in volume %) for up to 400 cycles. The kinetics and morphological development of these reactions were compared with those found during isothermal exposure to the same gases. Under isothermal conditions, all alloys developed thin protective chromium-rich scales in dry oxygen. Addition of 5% H2O induced breakaway for Fe-9Cr within 48 h, but had little effect on higher chromium alloys. Isothermal chromia scale growth on Fe-17Cr and Fe-25Cr was accelerated by the addition of 20% H2O, but breakaway did not result. Under cyclic conditions in dry oxygen, Fe-9Cr quickly entered breakaway, oxidising according to fast, linear kinetics, but the higher chromium alloys exhibited protective behaviour. When 5% H2O was added to the oxygen, the 17% Cr alloy also underwent fast breakaway oxidation, but Fe-25Cr continued to be protected by a chromia scale. In the 20% H2O gas, all alloys failed under cyclic conditions, producing thick, iron-rich oxide scales. The synergistic effects of water vapour and temperature cycling are discussed in terms of alloy chromium depletion and the effects of H2O(g) on oxide transport properties. DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005866/abstract [article] Effect of water vapour on cyclic oxidation of Fe–Cr alloys [texte imprimé] / N. K. Othman, Auteur ; J. Zhang, Auteur ; D. J. Young, Auteur . - 2011 . - pp. 496–503. Génie Mécanique Langues : Anglais (eng) in Materials and corrosion > Vol. 62 N° 6 (Juin 2011) . - pp. 496–503 Mots-clés : Alloy  depletion  Breakaway  Cyclic  oxidation Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Model Fe–Cr alloys containing 9, 17 or 25 wt% Cr were subjected to repeated 1 h cycles of exposure at 700 °C to flowing gas mixtures of Ar-20O2, Ar-20O2-5H2O and Ar-5O2-20H2O (all in volume %) for up to 400 cycles. The kinetics and morphological development of these reactions were compared with those found during isothermal exposure to the same gases. Under isothermal conditions, all alloys developed thin protective chromium-rich scales in dry oxygen. Addition of 5% H2O induced breakaway for Fe-9Cr within 48 h, but had little effect on higher chromium alloys. Isothermal chromia scale growth on Fe-17Cr and Fe-25Cr was accelerated by the addition of 20% H2O, but breakaway did not result. Under cyclic conditions in dry oxygen, Fe-9Cr quickly entered breakaway, oxidising according to fast, linear kinetics, but the higher chromium alloys exhibited protective behaviour. When 5% H2O was added to the oxygen, the 17% Cr alloy also underwent fast breakaway oxidation, but Fe-25Cr continued to be protected by a chromia scale. In the 20% H2O gas, all alloys failed under cyclic conditions, producing thick, iron-rich oxide scales. The synergistic effects of water vapour and temperature cycling are discussed in terms of alloy chromium depletion and the effects of H2O(g) on oxide transport properties. DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005866/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

Metal dusting behaviour of several nickel- and cobalt-base alloys in CO-H2-H2O atmosphere / Wu, Q. in Materials and corrosion, Vol. 62 N° 6 (Juin 2011) 

Public ISBD [article]  in Materials and corrosion > Vol. 62 N° 6 (Juin 2011) . - pp. 521–530 Titre : Metal dusting behaviour of several nickel- and cobalt-base alloys in CO-H2-H2O atmosphere Type de document : texte imprimé Auteurs : Wu, Q., Auteur ; J. Zhang, Auteur ; D. J. Young, Auteur Année de publication : 2011 Article en page(s) : pp. 521–530 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Carburization  Cobalt  Graphite  Iron  Metal  dusting  Nickel Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : The metal dusting behaviour of total 11 nickel- and cobalt-base alloys at 680 °C in a gas of 68%CO[BOND]31%H2[BOND]1%H2O (aC = 19.0, equation image = 5.4 × 10−25  atm) was investigated. All samples were electropolished and reacted in a thermal cycling apparatus. On the basis of their reaction kinetics, these alloys can be classified into three groups: the first, with rapid carbon uptake and significant metal wastage, consists of alloys of relatively high iron content (AC 66, 800H and NS-163); the second, with intermediate rates, consists of some Co-base alloys (HAYNES 188, HAYNES 25 and ULTIMET) and the third, with very low reaction rates, consists of nickel-base alloys with high chromium levels (601, HAYNES HR 160, 230, G-35 and EN 105). An external chromia scale protected group 3 alloys from carburization and dusting. However, this protective scale was damaged and not rehealed for group 1 and group 2 alloys, allowing carbon attack. In all cases, coke deposited on the surface with two typical morphologies: filaments and graphite particle clusters. Subsurface spinel formation in high iron-content alloys led to rapid dusting due to the significant volume expansion. Alloy carbon permeability was calculated from a simple law of mixtures, and shown to correlate reasonably well with initial dusting rate except for one cobalt-base alloy in which iron spinel formation was significant. DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005863/abstract [article] Metal dusting behaviour of several nickel- and cobalt-base alloys in CO-H2-H2O atmosphere [texte imprimé] / Wu, Q., Auteur ; J. Zhang, Auteur ; D. J. Young, Auteur . - 2011 . - pp. 521–530. Génie Mécanique Langues : Anglais (eng) in Materials and corrosion > Vol. 62 N° 6 (Juin 2011) . - pp. 521–530 Mots-clés : Carburization  Cobalt  Graphite  Iron  Metal  dusting  Nickel Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : The metal dusting behaviour of total 11 nickel- and cobalt-base alloys at 680 °C in a gas of 68%CO[BOND]31%H2[BOND]1%H2O (aC = 19.0, equation image = 5.4 × 10−25  atm) was investigated. All samples were electropolished and reacted in a thermal cycling apparatus. On the basis of their reaction kinetics, these alloys can be classified into three groups: the first, with rapid carbon uptake and significant metal wastage, consists of alloys of relatively high iron content (AC 66, 800H and NS-163); the second, with intermediate rates, consists of some Co-base alloys (HAYNES 188, HAYNES 25 and ULTIMET) and the third, with very low reaction rates, consists of nickel-base alloys with high chromium levels (601, HAYNES HR 160, 230, G-35 and EN 105). An external chromia scale protected group 3 alloys from carburization and dusting. However, this protective scale was damaged and not rehealed for group 1 and group 2 alloys, allowing carbon attack. In all cases, coke deposited on the surface with two typical morphologies: filaments and graphite particle clusters. Subsurface spinel formation in high iron-content alloys led to rapid dusting due to the significant volume expansion. Alloy carbon permeability was calculated from a simple law of mixtures, and shown to correlate reasonably well with initial dusting rate except for one cobalt-base alloy in which iron spinel formation was significant. DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005863/abstract

Oxidation kinetics of Y-doped FeCrAl-alloys in low and high pO2 gases / D. J. Young in Materials and corrosion, Vol. 61 N° 10 (Octobre 2010) 

Public ISBD [article]  in Materials and corrosion > Vol. 61 N° 10 (Octobre 2010) . - pp. 838–844 Titre : Oxidation kinetics of Y-doped FeCrAl-alloys in low and high pO2 gases Type de document : texte imprimé Auteurs : D. J. Young, Auteur ; D. Naumenko, Auteur ; L. Niewolak, Auteur Année de publication : 2011 Article en page(s) : pp. 838–844 Note générale : Génie mécanique Langues : Anglais (eng) Mots-clés : Alumina  scales;  grain  boundary  diffusion;  FeCrAlY  alloy;  oxidation  kinetics Résumé : A model Fe-20Cr-5Al-0.05Y alloy was oxidized in Ar-20%O2 and Ar-4%H2-7%H2O at 1200–1300 °C. Two-stage oxidation experiments using oxygen isotope tracers showed that inward oxygen diffusion was predominant in both gases, but more isotope exchange was observed in the H2/H2O gas reaction. The alumina scales formed in both gases were composed of columnar grains, the lateral size of which increased linearly with depth beneath the scale surface. Thermogravimetric measurement of oxygen uptake revealed kinetics which were intermediate to parabolic and cubic kinetic rate laws. A model based on grain boundary diffusion control coupled with competitive oxide grain growth accounts satisfactorily for the results when the requirement for a divergence-free flux within the scale is imposed. This treatment shows that the oxide grain boundary diffusion coefficient is lower when H2O is the oxidant. It is concluded that hydrogen slows the grain boundary diffusion process by altering the nature of the diffusing species. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.200905432/abstract [article] Oxidation kinetics of Y-doped FeCrAl-alloys in low and high pO2 gases [texte imprimé] / D. J. Young, Auteur ; D. Naumenko, Auteur ; L. Niewolak, Auteur . - 2011 . - pp. 838–844. Génie mécanique Langues : Anglais (eng) in Materials and corrosion > Vol. 61 N° 10 (Octobre 2010) . - pp. 838–844 Mots-clés : Alumina  scales;  grain  boundary  diffusion;  FeCrAlY  alloy;  oxidation  kinetics Résumé : A model Fe-20Cr-5Al-0.05Y alloy was oxidized in Ar-20%O2 and Ar-4%H2-7%H2O at 1200–1300 °C. Two-stage oxidation experiments using oxygen isotope tracers showed that inward oxygen diffusion was predominant in both gases, but more isotope exchange was observed in the H2/H2O gas reaction. The alumina scales formed in both gases were composed of columnar grains, the lateral size of which increased linearly with depth beneath the scale surface. Thermogravimetric measurement of oxygen uptake revealed kinetics which were intermediate to parabolic and cubic kinetic rate laws. A model based on grain boundary diffusion control coupled with competitive oxide grain growth accounts satisfactorily for the results when the requirement for a divergence-free flux within the scale is imposed. This treatment shows that the oxide grain boundary diffusion coefficient is lower when H2O is the oxidant. It is concluded that hydrogen slows the grain boundary diffusion process by altering the nature of the diffusing species. En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.200905432/abstract

Recent advances in understanding metal dusting / D. J. Young in Materials and corrosion, Vol. 62 N° 1 (Janvier 2011) 

Public ISBD [article]  in Materials and corrosion > Vol. 62 N° 1 (Janvier 2011) . - pp. 7–28 Titre : Recent advances in understanding metal dusting : a review Type de document : texte imprimé Auteurs : D. J. Young, Auteur ; J. Zhang, Auteur ; C. Geers, Auteur Année de publication : 2011 Article en page(s) : pp. 7–28 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : alloy  composition  Cementite  Coating  Coking  Metal  dusting  Second  phase  effect  Surface  catalysis Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Recent experimental investigations have widened the understanding of metal dusting significantly. Microscopic observations have been used to dissect dusting mechanisms. Iron dusts by growing a cementite surface scale, which catalyses graphite nucleation and growth. The resulting volume expansion leads to cementite disintegration. Cementite formation on iron can be suppressed by alloying with germanium. Nonetheless, dusting occurs via the direct growth of graphite into the metal, producing nanoparticles of ferrite. This process is faster, because carbon diffusion is more rapid in α-Fe than in Fe3C. Austenitic materials cannot form cementite, and dust via formation of graphite at external surfaces and interior grain boundaries. The coke deposit consists of carbon nanotubes with austenite particles at their tips, or graphite particles encapsulating austenite. TEM studies demonstrate the inward growth of graphite within the metal interior. It is therefore concluded that the dusting mechanism of austenitic materials like high alloy Cr–Ni steels and Ni base materials is one of graphite nucleation and growth within the near surface metal. In all alloys examined, both ferritic and austenitic, the principal mass transfer process is inward diffusion of carbon. Alloying iron with nickel leads to a transformation from one mechanism with carbide formation to the other without. Copper alloying in nickel and high nickel content stainless steels strongly suppresses graphite nucleation, as does also an intermetallic Ni–Sn phase, thereby reducing greatly the overall dusting rate. A surface layer of intermetallic Ni–Sn Fe-base materials facilitates the formation of a Fe3SnC surface scale which also prevents coking and metal dusting. Current understanding of the roles of temperature, gas composition and surface oxides on dusting rates are summarised. Finally, protection against metal dusting by coatings is discussed in terms of their effects on catalysis of carbon deposition, and on protective oxide formation. DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005675/abstract [article] Recent advances in understanding metal dusting : a review [texte imprimé] / D. J. Young, Auteur ; J. Zhang, Auteur ; C. Geers, Auteur . - 2011 . - pp. 7–28. Génie Mécanique Langues : Anglais (eng) in Materials and corrosion > Vol. 62 N° 1 (Janvier 2011) . - pp. 7–28 Mots-clés : alloy  composition  Cementite  Coating  Coking  Metal  dusting  Second  phase  effect  Surface  catalysis Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Recent experimental investigations have widened the understanding of metal dusting significantly. Microscopic observations have been used to dissect dusting mechanisms. Iron dusts by growing a cementite surface scale, which catalyses graphite nucleation and growth. The resulting volume expansion leads to cementite disintegration. Cementite formation on iron can be suppressed by alloying with germanium. Nonetheless, dusting occurs via the direct growth of graphite into the metal, producing nanoparticles of ferrite. This process is faster, because carbon diffusion is more rapid in α-Fe than in Fe3C. Austenitic materials cannot form cementite, and dust via formation of graphite at external surfaces and interior grain boundaries. The coke deposit consists of carbon nanotubes with austenite particles at their tips, or graphite particles encapsulating austenite. TEM studies demonstrate the inward growth of graphite within the metal interior. It is therefore concluded that the dusting mechanism of austenitic materials like high alloy Cr–Ni steels and Ni base materials is one of graphite nucleation and growth within the near surface metal. In all alloys examined, both ferritic and austenitic, the principal mass transfer process is inward diffusion of carbon. Alloying iron with nickel leads to a transformation from one mechanism with carbide formation to the other without. Copper alloying in nickel and high nickel content stainless steels strongly suppresses graphite nucleation, as does also an intermetallic Ni–Sn phase, thereby reducing greatly the overall dusting rate. A surface layer of intermetallic Ni–Sn Fe-base materials facilitates the formation of a Fe3SnC surface scale which also prevents coking and metal dusting. Current understanding of the roles of temperature, gas composition and surface oxides on dusting rates are summarised. Finally, protection against metal dusting by coatings is discussed in terms of their effects on catalysis of carbon deposition, and on protective oxide formation. DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005675/abstract