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Ajouter le résultat dans votre panierExperiences with high temperature corrosion at straw-firing power plants in Denmark / M. Montgomery in Materials and corrosion, Vol. 62 N° 7 (Juillet 2011)
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 593–605
Titre : Experiences with high temperature corrosion at straw-firing power plants in Denmark Type de document : texte imprimé Auteurs : M. Montgomery, Auteur ; S. A. Jensen, Auteur ; U. Borg, Auteur Année de publication : 2011 Article en page(s) : pp. 593–605 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Lifetime prediction Straw-firing TP347H Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : By the end of 2009, there will be eight biomass and five biomass co-firing plants in Denmark. Due to the steep increase of corrosion rate with respect to temperature in biomass plants, it is not viable to have similar steam data as fossil fuel plants. Thus for the newer plants, Maribo Sakskøbing, Avedøre 2 biomass boiler, Fyn 8 and Amager 1 (Fyn 8 and Amager 1 are under commissioning), the steam temperature of the final superheaters are approximately 540 °C and the steel type used is an 18–10 stainless steel, (TP347H). However there is still a need to monitor corrosion rates, and to collate data to enable better lifetime prediction of vulnerable components in straw-firing plants since the corrosion rates are so much faster than in coal firing plants. Therefore, there are continued investigations in recently commissioned plants with test tubes installed into actual superheaters. In addition temperature is measured on the specific tube loops where there are test tube sections. Thus a corrosion rate can be coupled to a temperature histogram. This is important since although a superheater has a defined steam outlet temperature, there is variation in the tube bundle due to variations of heat flux from the flue gas. This paper will describe the corrosion investigations for tube sections removed from Maribo Sakskøbing and Avedøre 2 biomass boiler which have been exposed for up to 30 000 h. In addition to monitoring the corrosion rates of actual components, there is a need to measure corrosion rates at higher temperatures to assess if there is a possibility to increase the outlet temperature of the plant, thus making the plant more cost effective. For this purpose Avedøre 2 biomass boiler has a test superheater loop fabricated in TP347H FG (the same material as the final superheaters). Some results from this test superheater will also be described. Effects of flue gas temperature and flue gas direction on corrosion rates are also discussed.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005856/abstract [article] Experiences with high temperature corrosion at straw-firing power plants in Denmark [texte imprimé] / M. Montgomery, Auteur ; S. A. Jensen, Auteur ; U. Borg, Auteur . - 2011 . - pp. 593–605.
Génie Mécanique
Langues : Anglais (eng)
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 593–605
Mots-clés : Lifetime prediction Straw-firing TP347H Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : By the end of 2009, there will be eight biomass and five biomass co-firing plants in Denmark. Due to the steep increase of corrosion rate with respect to temperature in biomass plants, it is not viable to have similar steam data as fossil fuel plants. Thus for the newer plants, Maribo Sakskøbing, Avedøre 2 biomass boiler, Fyn 8 and Amager 1 (Fyn 8 and Amager 1 are under commissioning), the steam temperature of the final superheaters are approximately 540 °C and the steel type used is an 18–10 stainless steel, (TP347H). However there is still a need to monitor corrosion rates, and to collate data to enable better lifetime prediction of vulnerable components in straw-firing plants since the corrosion rates are so much faster than in coal firing plants. Therefore, there are continued investigations in recently commissioned plants with test tubes installed into actual superheaters. In addition temperature is measured on the specific tube loops where there are test tube sections. Thus a corrosion rate can be coupled to a temperature histogram. This is important since although a superheater has a defined steam outlet temperature, there is variation in the tube bundle due to variations of heat flux from the flue gas. This paper will describe the corrosion investigations for tube sections removed from Maribo Sakskøbing and Avedøre 2 biomass boiler which have been exposed for up to 30 000 h. In addition to monitoring the corrosion rates of actual components, there is a need to measure corrosion rates at higher temperatures to assess if there is a possibility to increase the outlet temperature of the plant, thus making the plant more cost effective. For this purpose Avedøre 2 biomass boiler has a test superheater loop fabricated in TP347H FG (the same material as the final superheaters). Some results from this test superheater will also be described. Effects of flue gas temperature and flue gas direction on corrosion rates are also discussed.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005856/abstract
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 606–615
Titre : The influence of small amounts of KCl(s) on the high temperature corrosion of a Fe-2.25Cr-1Mo steel at 400 and 500°C Type de document : texte imprimé Auteurs : N. Folkeson, Auteur ; T. Jonsson, Auteur ; M. Halvarsson, Auteur Année de publication : 2011 Article en page(s) : pp. 606–615 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Alkali chloride Low alloyed steel Fe-2.25Cr-1Mo 400°C 500°C Grain boundary diffusion Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : This paper reports the oxidation behaviour of a low-alloyed steel (Fe-2.25Cr-1Mo) in the presence of small amounts of KCl(s) at 400 and 500°C. Cleaned and polished sample coupons were exposed in a horizontal tube furnace with exposure times ranging from one hour to one week. The flue gas composition was 5% O2 with 40% H2O in N2, and 0.1 mg KCl/cm2 was deposited on the samples prior to exposure. X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis were used to characterize the samples. Cross sections were prepared by means of focused ion beam (FIB) and broad ion beam (BIB). At 400°C there was a modest mass gain in the absence of KCl. In the presence of KCl, mass gain is significantly increased and a rapid attack is evident already after short exposure times. At 500°C, the mass gains in the absence of KCl were considerably higher than at 400°C, especially after 168 hours of exposure. KCl had an effect at shorter exposure times, but after one week the samples exposed with and without KCl had mass gains of comparable magnitude.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005942/abstract [article] The influence of small amounts of KCl(s) on the high temperature corrosion of a Fe-2.25Cr-1Mo steel at 400 and 500°C [texte imprimé] / N. Folkeson, Auteur ; T. Jonsson, Auteur ; M. Halvarsson, Auteur . - 2011 . - pp. 606–615.
Génie Mécanique
Langues : Anglais (eng)
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 606–615
Mots-clés : Alkali chloride Low alloyed steel Fe-2.25Cr-1Mo 400°C 500°C Grain boundary diffusion Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : This paper reports the oxidation behaviour of a low-alloyed steel (Fe-2.25Cr-1Mo) in the presence of small amounts of KCl(s) at 400 and 500°C. Cleaned and polished sample coupons were exposed in a horizontal tube furnace with exposure times ranging from one hour to one week. The flue gas composition was 5% O2 with 40% H2O in N2, and 0.1 mg KCl/cm2 was deposited on the samples prior to exposure. X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis were used to characterize the samples. Cross sections were prepared by means of focused ion beam (FIB) and broad ion beam (BIB). At 400°C there was a modest mass gain in the absence of KCl. In the presence of KCl, mass gain is significantly increased and a rapid attack is evident already after short exposure times. At 500°C, the mass gains in the absence of KCl were considerably higher than at 400°C, especially after 168 hours of exposure. KCl had an effect at shorter exposure times, but after one week the samples exposed with and without KCl had mass gains of comparable magnitude.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005942/abstract
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 616–622
Titre : Behaviour of ferritic stainless steels subjected to dry biogas atmospheres at high temperatures Type de document : texte imprimé Auteurs : P. Promdirek, Auteur ; G. Lothongkhum, Auteur ; S. Chandra-ambhorn, Auteur Année de publication : 2011 Article en page(s) : pp. 616–622 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : SOFC Ferritic stainless steels Biogas Oxidation Carburization Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : The objective of this study is to understand the high temperature corrosion behaviour of the ferritic stainless steel type AISI 441 (18CrTiNb), a candidate for SOFC interconnectors, under dry synthetic fermentation biogas (CH4 + CO2 mixtures), possibly used at the anode side of the cell. Thermodynamic analysis showed that, in such mixtures, the partial pressure of oxygen lies in the range of 10−23 to 10−20 bar for temperature between 700 and 900 °C and that the formation of solid carbon may take place in several conditions. XRD results confirmed the formation of Cr2O3 and Mn-Cr spinel, with a mixture of internal carbides. In this temperature range, kinetic experiments showed linear mass change. Comparing with the linear rate constants of 441 oxidised in pure CO2, corrosion in biogas was larger and increased with increasing the methane content in the biogas. The surface morphology of the corroded specimens showed a dense oxide scale at temperatures less than 800 °C, serving as an efficient barrier to carbon penetration. However, when the temperature reaches 900 °C, cracks and pores appear in the oxide scale, carbon can precipitate and diffuse easier than at 800 °C and may lead to internal carbide formation. In such biogas atmospheres, 800 °C seems the maximum operating temperature of devices containing this ferritic stainless steel.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005878/abstract [article] Behaviour of ferritic stainless steels subjected to dry biogas atmospheres at high temperatures [texte imprimé] / P. Promdirek, Auteur ; G. Lothongkhum, Auteur ; S. Chandra-ambhorn, Auteur . - 2011 . - pp. 616–622.
Génie Mécanique
Langues : Anglais (eng)
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 616–622
Mots-clés : SOFC Ferritic stainless steels Biogas Oxidation Carburization Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : The objective of this study is to understand the high temperature corrosion behaviour of the ferritic stainless steel type AISI 441 (18CrTiNb), a candidate for SOFC interconnectors, under dry synthetic fermentation biogas (CH4 + CO2 mixtures), possibly used at the anode side of the cell. Thermodynamic analysis showed that, in such mixtures, the partial pressure of oxygen lies in the range of 10−23 to 10−20 bar for temperature between 700 and 900 °C and that the formation of solid carbon may take place in several conditions. XRD results confirmed the formation of Cr2O3 and Mn-Cr spinel, with a mixture of internal carbides. In this temperature range, kinetic experiments showed linear mass change. Comparing with the linear rate constants of 441 oxidised in pure CO2, corrosion in biogas was larger and increased with increasing the methane content in the biogas. The surface morphology of the corroded specimens showed a dense oxide scale at temperatures less than 800 °C, serving as an efficient barrier to carbon penetration. However, when the temperature reaches 900 °C, cracks and pores appear in the oxide scale, carbon can precipitate and diffuse easier than at 800 °C and may lead to internal carbide formation. In such biogas atmospheres, 800 °C seems the maximum operating temperature of devices containing this ferritic stainless steel.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005878/abstract
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 623–634
Titre : A new approach to improve high temperature corrosion resistance of thermally sprayed coatings by using electrochemical corrosion tests Type de document : texte imprimé Auteurs : T. Neddemeyer, Auteur ; M. Mocker, Auteur ; M. Faulstich, Auteur Année de publication : 2011 Article en page(s) : pp. 623–634 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Corrosion protection Diamalloy 1005 Electrochemical tests in aqueous solution High temperature corrosion tests Thermal spraying Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : In order to increase reliability and lifetime of heat exchangers in waste-to-energy plants corrosion resistant thermally sprayed coatings are applied in a higher extent. From the selection of a plant specific spray material and process via laboratory and field experiments up to a successful coating a high amount of time and money is necessary. In particular, experiments in corrosive surroundings at high temperature which are needed to optimize the coating quality are time-consuming. In order to decrease development times and to reduce costs, corrosion resistance of a thermally sprayed coating under high temperature conditions is compared with its behavior in an aqueous solution. If the high temperature corrosion resistance can be forecast by electrochemical tests, a fast, efficient and cheap possibility to improve the coating quality would be available and the efforts for tests in high temperature environments could be decreased. To accomplish this objective, Diamalloy 1005 was sprayed with the APS-process on a ferritic steel. Since the performance of thermally sprayed coatings is not only influenced by the coating material but also by the spraying parameters, three different spray parameter sets were used.
After analyzing the results of the corrosion tests under high temperature conditions and in aqueous solution an identical assessment of the spray parameter-specific corrosion protection could be obtained. Ongoing field tests in a waste-to-energy plant are expected to prove the laboratory results. So, a first step in the development of a fast, efficient and cheap method to predict the high temperature corrosion resistance of a thermally sprayed coating might have been done.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005860/abstract [article] A new approach to improve high temperature corrosion resistance of thermally sprayed coatings by using electrochemical corrosion tests [texte imprimé] / T. Neddemeyer, Auteur ; M. Mocker, Auteur ; M. Faulstich, Auteur . - 2011 . - pp. 623–634.
Génie Mécanique
Langues : Anglais (eng)
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 623–634
Mots-clés : Corrosion protection Diamalloy 1005 Electrochemical tests in aqueous solution High temperature corrosion tests Thermal spraying Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : In order to increase reliability and lifetime of heat exchangers in waste-to-energy plants corrosion resistant thermally sprayed coatings are applied in a higher extent. From the selection of a plant specific spray material and process via laboratory and field experiments up to a successful coating a high amount of time and money is necessary. In particular, experiments in corrosive surroundings at high temperature which are needed to optimize the coating quality are time-consuming. In order to decrease development times and to reduce costs, corrosion resistance of a thermally sprayed coating under high temperature conditions is compared with its behavior in an aqueous solution. If the high temperature corrosion resistance can be forecast by electrochemical tests, a fast, efficient and cheap possibility to improve the coating quality would be available and the efforts for tests in high temperature environments could be decreased. To accomplish this objective, Diamalloy 1005 was sprayed with the APS-process on a ferritic steel. Since the performance of thermally sprayed coatings is not only influenced by the coating material but also by the spraying parameters, three different spray parameter sets were used.
After analyzing the results of the corrosion tests under high temperature conditions and in aqueous solution an identical assessment of the spray parameter-specific corrosion protection could be obtained. Ongoing field tests in a waste-to-energy plant are expected to prove the laboratory results. So, a first step in the development of a fast, efficient and cheap method to predict the high temperature corrosion resistance of a thermally sprayed coating might have been done.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005860/abstract
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 635–641
Titre : A thermodynamic study of the gaseous potassium chemistry in the convection sections of biomass fired boilers Type de document : texte imprimé Auteurs : T. Blomberg, Auteur Année de publication : 2011 Article en page(s) : pp. 635–641 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Alkali Biomass Deposit Fouling Hot corrosion Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Thermodynamic calculations of the gaseous potassium species in boiler flue gases are presented. Results show that if the K(g)/Cl(g) molar ratio is still higher than 1 after the K2SO4(s) aerosol formation at high gas temperatures, the excess potassium is in the form of KOH(g). K(g)/Cl(g) molar ratios at the inlet of the convection section for biomass fired boilers were estimated from the chemical analysis of the fuels, with the assumption that all the fuel sulfur had reacted to K2SO4(s) aerosols before the inlet of the convection section. 0–100% conversion of fuel alkali to vaporized alkali was calculated. Generally, if the conversion was more than 60%, the calculated ratios for biomass fuels were higher than 1. Furthermore, due to the thermodynamic instability of K2CO3(g), it is likely that the formation of K2CO3(s) on the heat transfer surfaces follows a heterogeneous route where KOH(l,s) is transformed to K2CO3(s) at the surface, not in the gas phase. This leads to a possible formation of a basic salt melt on the heat transfer surfaces and thus alloying with Cr may be ineffective in improving the hot corrosion resistance of steels in these environments. Based on the literature data of oxide solubilities in basic alkali melts, it is suggested that alloying with Ni or Co will provide better protection in these applications.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005880/abstract [article] A thermodynamic study of the gaseous potassium chemistry in the convection sections of biomass fired boilers [texte imprimé] / T. Blomberg, Auteur . - 2011 . - pp. 635–641.
Génie Mécanique
Langues : Anglais (eng)
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 635–641
Mots-clés : Alkali Biomass Deposit Fouling Hot corrosion Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Thermodynamic calculations of the gaseous potassium species in boiler flue gases are presented. Results show that if the K(g)/Cl(g) molar ratio is still higher than 1 after the K2SO4(s) aerosol formation at high gas temperatures, the excess potassium is in the form of KOH(g). K(g)/Cl(g) molar ratios at the inlet of the convection section for biomass fired boilers were estimated from the chemical analysis of the fuels, with the assumption that all the fuel sulfur had reacted to K2SO4(s) aerosols before the inlet of the convection section. 0–100% conversion of fuel alkali to vaporized alkali was calculated. Generally, if the conversion was more than 60%, the calculated ratios for biomass fuels were higher than 1. Furthermore, due to the thermodynamic instability of K2CO3(g), it is likely that the formation of K2CO3(s) on the heat transfer surfaces follows a heterogeneous route where KOH(l,s) is transformed to K2CO3(s) at the surface, not in the gas phase. This leads to a possible formation of a basic salt melt on the heat transfer surfaces and thus alloying with Cr may be ineffective in improving the hot corrosion resistance of steels in these environments. Based on the literature data of oxide solubilities in basic alkali melts, it is suggested that alloying with Ni or Co will provide better protection in these applications.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005880/abstract
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 642–649
Titre : Optimised selection of new protective coatings for biofuel boiler applications Type de document : texte imprimé Auteurs : S. Tuurna, Auteur ; T. Varis, Auteur ; K. Penttil, Auteur Année de publication : 2011 Article en page(s) : pp. 642–649 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Biofuel boiler Coating performance Life extension Protection Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Using biofuels in power and CHP boilers can pose a challenge for materials performance. Formation of deposits containing e.g. potassium, sulphur, calcium, sodium, and chlorine can result in severe corrosion of conventional steels and alloys at relatively modest temperatures. Given suitable component design and fabrication facilities, coatings may be considered to protect the fireside surfaces. This paper aims to present a systematic approach to the design and selection criteria for protective coatings of boilers. The approach includes modelling of the process and surface conditions, optimisation of the coating process and structure, and performance validation in the laboratory and plant scales. The applied examples have included iron and nickel based HVOF and arc sprayed coatings subjected to verification field testing in boiler testing under aggressive biofuel conditions. The coatings have shown good corrosion resistance in both laboratory tests and long-term harsh field tests. The paper discusses the used approach for finding a suitable and cost effective coating for biofuel boiler applications. The paper gives test results from microstructural, corrosion resistance and field testing experience for the selected coatings
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005898/abstract [article] Optimised selection of new protective coatings for biofuel boiler applications [texte imprimé] / S. Tuurna, Auteur ; T. Varis, Auteur ; K. Penttil, Auteur . - 2011 . - pp. 642–649.
Génie Mécanique
Langues : Anglais (eng)
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 642–649
Mots-clés : Biofuel boiler Coating performance Life extension Protection Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Using biofuels in power and CHP boilers can pose a challenge for materials performance. Formation of deposits containing e.g. potassium, sulphur, calcium, sodium, and chlorine can result in severe corrosion of conventional steels and alloys at relatively modest temperatures. Given suitable component design and fabrication facilities, coatings may be considered to protect the fireside surfaces. This paper aims to present a systematic approach to the design and selection criteria for protective coatings of boilers. The approach includes modelling of the process and surface conditions, optimisation of the coating process and structure, and performance validation in the laboratory and plant scales. The applied examples have included iron and nickel based HVOF and arc sprayed coatings subjected to verification field testing in boiler testing under aggressive biofuel conditions. The coatings have shown good corrosion resistance in both laboratory tests and long-term harsh field tests. The paper discusses the used approach for finding a suitable and cost effective coating for biofuel boiler applications. The paper gives test results from microstructural, corrosion resistance and field testing experience for the selected coatings
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005898/abstract
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 650–658
Titre : Metallic interconnects for solid oxide fuel cell: Performance of reactive element oxide coating during long time exposure Type de document : texte imprimé Auteurs : S. Fontana, Auteur ; S. Chevalier, Auteur ; G. Caboche, Auteur Année de publication : 2011 Article en page(s) : pp. 650–658 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Metallic interconnect MOCVD Reactive element SOFC Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : One of challenges in improving the performance and cost-effectiveness of SOFCs (solid oxide fuel cells) is the development of suitable interconnects materials. Chromia-forming alloys and especially ferritic stainless steels, like Crofer22APU, are considered to be among the most promising candidate materials as interconnects in SOFC stacks. However, the performance of chromia-forming materials can be limited by the low electronic conductivity of the oxide scale (high ASR – area specific resistance – value). Such degradation are unacceptable regarding the long-term operation (>40 000 h). A previous study 1 demonstrated that in air, the addition of a nanometric reactive element oxide (La2O3) layer applied by metal organic chemical vapor deposition (MOCVD) drastically improved both corrosion rate and electrical properties of Crofer22APU and Haynes230 alloys for 100 h at 800 °C. In this present study coating performances were checked after 10 months (7500 h) and 20 months (15 000 h) at 800 °C in air. The corrosion products were carefully analyzed by SEM, EDX, and XRD. ASR measurements are realized after long time exposure. This study demonstrates that the Crofer22APU alloy has a good oxidation resistance after 15 000 h in air but this alloy has an ASR value equal to 0.370 Ω cm2. The coatings composed of a thin reactive element oxide such as La2O3 resulted in an important improvement in the high temperature oxidation resistance; the ASR values are equal to 0.154 Ω cm2. Haynes230 alloy has a better oxidation resistance but the formation of an insulating Al2O3/SiO2 layer could be detrimental.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005857/abstract [article] Metallic interconnects for solid oxide fuel cell: Performance of reactive element oxide coating during long time exposure [texte imprimé] / S. Fontana, Auteur ; S. Chevalier, Auteur ; G. Caboche, Auteur . - 2011 . - pp. 650–658.
Génie Mécanique
Langues : Anglais (eng)
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 650–658
Mots-clés : Metallic interconnect MOCVD Reactive element SOFC Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : One of challenges in improving the performance and cost-effectiveness of SOFCs (solid oxide fuel cells) is the development of suitable interconnects materials. Chromia-forming alloys and especially ferritic stainless steels, like Crofer22APU, are considered to be among the most promising candidate materials as interconnects in SOFC stacks. However, the performance of chromia-forming materials can be limited by the low electronic conductivity of the oxide scale (high ASR – area specific resistance – value). Such degradation are unacceptable regarding the long-term operation (>40 000 h). A previous study 1 demonstrated that in air, the addition of a nanometric reactive element oxide (La2O3) layer applied by metal organic chemical vapor deposition (MOCVD) drastically improved both corrosion rate and electrical properties of Crofer22APU and Haynes230 alloys for 100 h at 800 °C. In this present study coating performances were checked after 10 months (7500 h) and 20 months (15 000 h) at 800 °C in air. The corrosion products were carefully analyzed by SEM, EDX, and XRD. ASR measurements are realized after long time exposure. This study demonstrates that the Crofer22APU alloy has a good oxidation resistance after 15 000 h in air but this alloy has an ASR value equal to 0.370 Ω cm2. The coatings composed of a thin reactive element oxide such as La2O3 resulted in an important improvement in the high temperature oxidation resistance; the ASR values are equal to 0.154 Ω cm2. Haynes230 alloy has a better oxidation resistance but the formation of an insulating Al2O3/SiO2 layer could be detrimental.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005857/abstract
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 659–667
Titre : High-temperature oxidation resistance of Al2O3-forming heat-resisting alloys with noble metal and rare earth additions Type de document : texte imprimé Auteurs : T. Amano, Auteur Année de publication : 2011 Article en page(s) : pp. 659–667 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Alumina Noble metals Scale adherence Water–vapor Yttrium Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : High-temperature oxidation behavior of Al2O3-forming heat-resisting alloys with noble metal (palladium, platinum, gold) and rare earth (yttrium) additions was studied in oxidizing atmospheres (oxygen, oxygen-water vapor) for 18 ks at 1473, 1573, and 1673 K, by mass gain measurements, amount of spalled oxide, observation of surface appearance, X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and transmission electron microscopy (TEM). Mass gains of all the Al2O3-forming Fe-20Cr-4Al alloys increased with increasing oxidation temperatures in both oxidation conditions. After oxidation in oxygen, the mass gains of the alloys with noble metal were almost the same values after any oxidation temperature. The mass gain of the alloys with yttrium decreased with increase in yttrium addition up to 0.1 mass%, and then tended to increase with 0.5 mass% yttrium addition at all oxidation temperatures studied. The amount of spalled oxide from the Fe-20Cr-4Al (A4) alloy showed the biggest value at 1573 K-oxidation, and then decreased in the order of 1473 K, 1673 K. On the other hand, the amount of spalled oxide from the other alloys decreased compared with the A4 alloy. No spalled oxide from 0.5Pt, 0.05Y, and 0.5Y alloys was observed at any oxidation temperature. After oxidation in an oxygen-water vapor mixture (dew point: 353 K), the mass gain of all the alloys showed similar values to that obtained in oxygen after any oxidation temperature. The amount of spalled oxide from the A4 alloy was about the same after oxidation at 1473 and 1573 K in oxygen, but then was higher when oxidized at 1673 K. The amount of spalled oxide from the other alloys obtained in oxygen–water vapor increased compared with those obtained in oxygen. On the other hand, the amount of spalled oxide from the 0.5Y alloy was zero after any oxidation temperature, and that from the 0.5Pt alloy was also zero after 1673 K-oxidation.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005855/abstract [article] High-temperature oxidation resistance of Al2O3-forming heat-resisting alloys with noble metal and rare earth additions [texte imprimé] / T. Amano, Auteur . - 2011 . - pp. 659–667.
Génie Mécanique
Langues : Anglais (eng)
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 659–667
Mots-clés : Alumina Noble metals Scale adherence Water–vapor Yttrium Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : High-temperature oxidation behavior of Al2O3-forming heat-resisting alloys with noble metal (palladium, platinum, gold) and rare earth (yttrium) additions was studied in oxidizing atmospheres (oxygen, oxygen-water vapor) for 18 ks at 1473, 1573, and 1673 K, by mass gain measurements, amount of spalled oxide, observation of surface appearance, X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and transmission electron microscopy (TEM). Mass gains of all the Al2O3-forming Fe-20Cr-4Al alloys increased with increasing oxidation temperatures in both oxidation conditions. After oxidation in oxygen, the mass gains of the alloys with noble metal were almost the same values after any oxidation temperature. The mass gain of the alloys with yttrium decreased with increase in yttrium addition up to 0.1 mass%, and then tended to increase with 0.5 mass% yttrium addition at all oxidation temperatures studied. The amount of spalled oxide from the Fe-20Cr-4Al (A4) alloy showed the biggest value at 1573 K-oxidation, and then decreased in the order of 1473 K, 1673 K. On the other hand, the amount of spalled oxide from the other alloys decreased compared with the A4 alloy. No spalled oxide from 0.5Pt, 0.05Y, and 0.5Y alloys was observed at any oxidation temperature. After oxidation in an oxygen-water vapor mixture (dew point: 353 K), the mass gain of all the alloys showed similar values to that obtained in oxygen after any oxidation temperature. The amount of spalled oxide from the A4 alloy was about the same after oxidation at 1473 and 1573 K in oxygen, but then was higher when oxidized at 1673 K. The amount of spalled oxide from the other alloys obtained in oxygen–water vapor increased compared with those obtained in oxygen. On the other hand, the amount of spalled oxide from the 0.5Y alloy was zero after any oxidation temperature, and that from the 0.5Pt alloy was also zero after 1673 K-oxidation.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005855/abstract
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 668–673
Titre : A chromia forming thermal barrier coating system Type de document : texte imprimé Auteurs : M. P. Taylor, Auteur ; H. E. Evans, Auteur ; S. Gray, Auteur Année de publication : 2011 Article en page(s) : pp. 668–673 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Thermal barrier coatings Chromia-forming bond coat Oxidation Hot corrosion Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Conventional thermal barrier coating (TBC) systems consist of an insulating ceramic topcoat, a bond coat for oxidation protection and the underlying superalloy designed to combat the oxidising conditions in aero- and land-based gas turbines. Under high-temperature oxidation, the use of an alumina forming bond coat is warranted, thus all current TBC systems are optimised for the early formation of a dense, protective thermally grown oxide (TGO) of alumina. This also offers protection against Type I hot corrosion but a chromia layer gives better protection against Type II corrosion and intermediate temperatures, the conditions found in land-based gas turbines.
In this paper the authors present the first known results for a chromia forming TBC system. Tests have been performed under oxidising conditions, up to 1000 h, at temperatures between 750 °C and 900 °C, and under Type I (900 °C) and Type II (700 °C) hot corrosion conditions up to 500 h. Under all these conditions no cracking, spallation or degradation was observed. Examination showed the formation of an adherent, dense chromia TGO at the bond coat / topcoat interface. These initial results are very encouraging and the TGO thicknesses agree well with comparable results reported in the literature.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005881/abstract [article] A chromia forming thermal barrier coating system [texte imprimé] / M. P. Taylor, Auteur ; H. E. Evans, Auteur ; S. Gray, Auteur . - 2011 . - pp. 668–673.
Génie Mécanique
Langues : Anglais (eng)
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 668–673
Mots-clés : Thermal barrier coatings Chromia-forming bond coat Oxidation Hot corrosion Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Conventional thermal barrier coating (TBC) systems consist of an insulating ceramic topcoat, a bond coat for oxidation protection and the underlying superalloy designed to combat the oxidising conditions in aero- and land-based gas turbines. Under high-temperature oxidation, the use of an alumina forming bond coat is warranted, thus all current TBC systems are optimised for the early formation of a dense, protective thermally grown oxide (TGO) of alumina. This also offers protection against Type I hot corrosion but a chromia layer gives better protection against Type II corrosion and intermediate temperatures, the conditions found in land-based gas turbines.
In this paper the authors present the first known results for a chromia forming TBC system. Tests have been performed under oxidising conditions, up to 1000 h, at temperatures between 750 °C and 900 °C, and under Type I (900 °C) and Type II (700 °C) hot corrosion conditions up to 500 h. Under all these conditions no cracking, spallation or degradation was observed. Examination showed the formation of an adherent, dense chromia TGO at the bond coat / topcoat interface. These initial results are very encouraging and the TGO thicknesses agree well with comparable results reported in the literature.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005881/abstract
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 674–680
Titre : Microstructural investigation of PGM-based alloy coatings for oxidation protection Type de document : texte imprimé Auteurs : Y. Song, Auteur ; C. Zhou, Auteur ; H. Murakami, Auteur Année de publication : 2011 Article en page(s) : pp. 674–680 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Cyclic oxidation Pt/Ir-modified Pt/Ru-modified Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : It is well known that Pt addition significantly improves the resistance of aluminide coatings to high-temperature oxidation and hot corrosion, which has led to the widespread application of Pt modified aluminide coatings on the superalloy components of advanced gas turbine engines.
Other platinum group metals (PGMs) such as Ir and Ru attract researchers for high temperature applications. In this study, oxidation properties of Pt-Ir and Pt-Ru based alloy coatings were investigated. Pt, Ru, and Ir were electroplated on a directionally solidified Ni-base superalloy DZ125. The cyclic oxidation test revealed that both Pt-Ir and Pt-Ru alloys exhibited good oxidation performance. The effect of substrate alloy and coating compositions on microstructural changes during cyclic oxidation tests were discussed.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005877/abstract [article] Microstructural investigation of PGM-based alloy coatings for oxidation protection [texte imprimé] / Y. Song, Auteur ; C. Zhou, Auteur ; H. Murakami, Auteur . - 2011 . - pp. 674–680.
Génie Mécanique
Langues : Anglais (eng)
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 674–680
Mots-clés : Cyclic oxidation Pt/Ir-modified Pt/Ru-modified Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : It is well known that Pt addition significantly improves the resistance of aluminide coatings to high-temperature oxidation and hot corrosion, which has led to the widespread application of Pt modified aluminide coatings on the superalloy components of advanced gas turbine engines.
Other platinum group metals (PGMs) such as Ir and Ru attract researchers for high temperature applications. In this study, oxidation properties of Pt-Ir and Pt-Ru based alloy coatings were investigated. Pt, Ru, and Ir were electroplated on a directionally solidified Ni-base superalloy DZ125. The cyclic oxidation test revealed that both Pt-Ir and Pt-Ru alloys exhibited good oxidation performance. The effect of substrate alloy and coating compositions on microstructural changes during cyclic oxidation tests were discussed.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005877/abstract
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 681–686
Titre : Internal surface protection of gas turbine blade by Si-aluminide coating Type de document : texte imprimé Auteurs : A. Firouzi, Auteur ; K. Shirvani, Auteur Année de publication : 2011 Article en page(s) : pp. 681–686 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Aluminide coating Blade Cooling passages Silicon Slurry Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : A laboratory-scale slurry silicoaluminizing process has been developed to apply coating into cooling passageways of a first-stage gas turbine blade. Analytical techniques for characterizing the coatings comprised optical microscopy, SEM, EDS, and XRD. The results of metallographic examinations demonstrated that acceptable coatings had been formed in almost all of the passageways. The amounts of Al and Si in the topcoat were found to be in the ranges of 24–26 wt% and 4.5–6 wt%, respectively. The heat treated coating consisted largely of β-NiAl phase as the coating matrix with uniform distribution of <2 µm-size precipitates. In addition, oxidation and hot corrosion performance of the coatings were investigated by cyclic exposure to 1100 °C and the furnace method using a mixture of sodium sulfate-40 wt% sodium vanadate-10 wt% sodium chloride at 780 °C, respectively. It was found that the presence of Si in the coating improves both oxidation and hot corrosion Type II properties.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005854/abstract [article] Internal surface protection of gas turbine blade by Si-aluminide coating [texte imprimé] / A. Firouzi, Auteur ; K. Shirvani, Auteur . - 2011 . - pp. 681–686.
Génie Mécanique
Langues : Anglais (eng)
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 681–686
Mots-clés : Aluminide coating Blade Cooling passages Silicon Slurry Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : A laboratory-scale slurry silicoaluminizing process has been developed to apply coating into cooling passageways of a first-stage gas turbine blade. Analytical techniques for characterizing the coatings comprised optical microscopy, SEM, EDS, and XRD. The results of metallographic examinations demonstrated that acceptable coatings had been formed in almost all of the passageways. The amounts of Al and Si in the topcoat were found to be in the ranges of 24–26 wt% and 4.5–6 wt%, respectively. The heat treated coating consisted largely of β-NiAl phase as the coating matrix with uniform distribution of <2 µm-size precipitates. In addition, oxidation and hot corrosion performance of the coatings were investigated by cyclic exposure to 1100 °C and the furnace method using a mixture of sodium sulfate-40 wt% sodium vanadate-10 wt% sodium chloride at 780 °C, respectively. It was found that the presence of Si in the coating improves both oxidation and hot corrosion Type II properties.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005854/abstract
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 687–694
Titre : Oxidation protection of Ni-base superalloys by halogen treatment Type de document : texte imprimé Auteurs : H.-E. Zschau, Auteur ; P. J. Masset, Auteur ; M. Schutze, Auteur Année de publication : 2011 Article en page(s) : pp. 687–694 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Borderline materials Halogen effect Ion implantation Ni-base superalloys Protective alumina scale Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : A new concept of oxidation protection is proposed for Ni-base alloys with Al-amounts of 2–5 wt%. Following Wagner's theory of oxidation the formation of a dense protective alumina scale is possible if the Al-activity is sufficiently high. This condition can be fulfilled by using the halogen effect. Thermodynamical calculations reveal the existence of regions for a positive effect of F and Cl for the alloys IN738 and IN939. In the case of fluorine these results are transformed into F concentrations in a screening by using ion implantation. By the F-effect the oxidation mechanism at 1050 °C/air was changed from internal oxidation of Al to an external formation of an Al2O3 – scale. Optimal implantation parameters were defined. The formation and stability of the protective alumina scale was proved within 1000 h/1050 °C.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005879/abstract [article] Oxidation protection of Ni-base superalloys by halogen treatment [texte imprimé] / H.-E. Zschau, Auteur ; P. J. Masset, Auteur ; M. Schutze, Auteur . - 2011 . - pp. 687–694.
Génie Mécanique
Langues : Anglais (eng)
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 687–694
Mots-clés : Borderline materials Halogen effect Ion implantation Ni-base superalloys Protective alumina scale Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : A new concept of oxidation protection is proposed for Ni-base alloys with Al-amounts of 2–5 wt%. Following Wagner's theory of oxidation the formation of a dense protective alumina scale is possible if the Al-activity is sufficiently high. This condition can be fulfilled by using the halogen effect. Thermodynamical calculations reveal the existence of regions for a positive effect of F and Cl for the alloys IN738 and IN939. In the case of fluorine these results are transformed into F concentrations in a screening by using ion implantation. By the F-effect the oxidation mechanism at 1050 °C/air was changed from internal oxidation of Al to an external formation of an Al2O3 – scale. Optimal implantation parameters were defined. The formation and stability of the protective alumina scale was proved within 1000 h/1050 °C.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005879/abstract
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 695–698
Titre : Combined Al- plus F-treatment of Ti-alloys for improved behaviour at elevated temperatures Type de document : texte imprimé Auteurs : A. Donchev, Auteur ; A. Kolitsch, Auteur ; M. Schutze, Auteur Année de publication : 2011 Article en page(s) : pp. 695–698 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Environmental embrittlement Oxidation Titanium Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Titanium is a widely used structural material because of its low specific weight, good mechanical properties and excellent corrosion resistance at ambient temperature. As a result of increased oxidation at elevated temperatures and environmental embrittlement the maximum operation temperature of standard Ti-alloys is only about 600 °C. The oxidation behaviour can be improved by different methods, e.g. coatings. This leads to an improvement which is, however, often limited. The combination of Al-enrichment in the sub surface zone, so that a TiAl-layer is formed, plus F-treatment gives impressively good results because a protective alumina scale is formed due to the fluorine effect. This alumina scale prevents oxygen inward diffusion which causes embrittlement and protects the material against environmental attack. The procedure is applied to alloys with a very low Al-content or even no Al at all. In the paper results of oxidation tests of α-Ti without any treatment, with Al-treatment and with a combination of Al- + F-treatment are presented. Aluminium was diffused into the samples by a powder pack process. Fluorine was applied by a liquid phase process. The formation of an alumina scale on treated samples was revealed by post experimental investigations. The results are discussed referring to the fluorine effect model for TiAl-alloys.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005870/abstract [article] Combined Al- plus F-treatment of Ti-alloys for improved behaviour at elevated temperatures [texte imprimé] / A. Donchev, Auteur ; A. Kolitsch, Auteur ; M. Schutze, Auteur . - 2011 . - pp. 695–698.
Génie Mécanique
Langues : Anglais (eng)
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 695–698
Mots-clés : Environmental embrittlement Oxidation Titanium Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Titanium is a widely used structural material because of its low specific weight, good mechanical properties and excellent corrosion resistance at ambient temperature. As a result of increased oxidation at elevated temperatures and environmental embrittlement the maximum operation temperature of standard Ti-alloys is only about 600 °C. The oxidation behaviour can be improved by different methods, e.g. coatings. This leads to an improvement which is, however, often limited. The combination of Al-enrichment in the sub surface zone, so that a TiAl-layer is formed, plus F-treatment gives impressively good results because a protective alumina scale is formed due to the fluorine effect. This alumina scale prevents oxygen inward diffusion which causes embrittlement and protects the material against environmental attack. The procedure is applied to alloys with a very low Al-content or even no Al at all. In the paper results of oxidation tests of α-Ti without any treatment, with Al-treatment and with a combination of Al- + F-treatment are presented. Aluminium was diffused into the samples by a powder pack process. Fluorine was applied by a liquid phase process. The formation of an alumina scale on treated samples was revealed by post experimental investigations. The results are discussed referring to the fluorine effect model for TiAl-alloys.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005870/abstract
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 699–705
Titre : Effect of atmosphere composition on the oxidation behavior of MCrAlY coatings Type de document : texte imprimé Auteurs : P. Song, Auteur ; M. Subanovic, Auteur ; J. Toscano, Auteur Année de publication : 2011 Article en page(s) : pp. 699–705 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : MCrAlY-bondcoat H2/H2O Oxidation TBC Zr Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : In the present work the effect of atmosphere composition on the growth rate and adherence of the alumina scales was studied using free-standing MCrAlY-coatings and TBC-specimens with MCrAlY-bondcoats. The exposures comprised isothermal and cyclic exposures in laboratory air and Ar-H2-H2O at 1100 °C.
It is shown that minor Zr-addition to the bondcoat results in enhanced scale growth and internal oxidation. This effect is independent of the atmosphere composition. As a consequence of the rapid oxide formation the times to TBC failure on the Zr-containing bondcoat in both atmospheres were much shorter compared to those with Zr-free bondcoat. In the latter case the formation of a thin compact alumina TGO was slower in H2/H2O than in air resulting in significantly longer TBC-lifetime in the former atmosphere.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005851/abstract [article] Effect of atmosphere composition on the oxidation behavior of MCrAlY coatings [texte imprimé] / P. Song, Auteur ; M. Subanovic, Auteur ; J. Toscano, Auteur . - 2011 . - pp. 699–705.
Génie Mécanique
Langues : Anglais (eng)
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 699–705
Mots-clés : MCrAlY-bondcoat H2/H2O Oxidation TBC Zr Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : In the present work the effect of atmosphere composition on the growth rate and adherence of the alumina scales was studied using free-standing MCrAlY-coatings and TBC-specimens with MCrAlY-bondcoats. The exposures comprised isothermal and cyclic exposures in laboratory air and Ar-H2-H2O at 1100 °C.
It is shown that minor Zr-addition to the bondcoat results in enhanced scale growth and internal oxidation. This effect is independent of the atmosphere composition. As a consequence of the rapid oxide formation the times to TBC failure on the Zr-containing bondcoat in both atmospheres were much shorter compared to those with Zr-free bondcoat. In the latter case the formation of a thin compact alumina TGO was slower in H2/H2O than in air resulting in significantly longer TBC-lifetime in the former atmosphere.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005851/abstract
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 706–712
Titre : Depletion sensor for protective high temperature coatings Type de document : texte imprimé Auteurs : K. Aleksandrov, Auteur ; M. Schutze, Auteur ; I. Teliban, Auteur Année de publication : 2011 Article en page(s) : pp. 706–712 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Alloy depletion Magnetic phases Pack cementation Protective coatings Sputtering Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : In order to minimise corrosion at high temperatures metallic or intermetallic Al- and/or Cr-rich protective coatings are applied to metallic alloys. Protection against corrosion is achieved by the formation of a continuous Al2O3 and/or Cr2O3 layer. Progressive scale formation, as well as interdiffusion between the coating and the substrate during long operating stages depletes the scale-forming elements, Al and Cr. The decrease of their concentration below a critical value is followed by accelerated corrosion and rapid breakdown of the component. Non-destructive depletion measurement is not possible, because of the absence of suitable materials that serve simultaneously as depletion sensors and reservoir phases. In a novel development, protective high temperature coatings containing a magnetic phase which at the same time acts as a reservoir phase are used as a depletion sensor. The alloy surface is coated with the magnetic substance either by reactive magnetron co-sputtering or by using pack cementation. In the course of operation, the formation of a protective oxide scale depletes the reservoir and the measured magnetic signal decreases. Measurement of the change of the coating's magnetic signal enables in situ assessment and non-destructive detection of depletion. In order to avoid perturbances in the magnetic signal coming from the coating the metallic substrate must be non-magnetic. Therefore this concept is restricted to Cr/Ni-austenitic steels and Ni-base alloys. Doping of AlN with transition metals (Al1 − xMexN, Me = Cr, Co, Mn, x = 2–7 at%) makes it a suitable magnetic reservoir phase, i.e. Al- and/or Cr-containing. Furthermore, it is ferromagnetic, has a high Curie temperature and is magnetically soft. Samples of Alloy 800 and Alloy 602 CA were coated with Al1 − xCrxN (x = 2 and 3 at%) using both pack cementation and PVD. Measurements of the magnetic moments of the coatings at temperatures up to 300 °C show very soft ferromagnetic behaviour. Coatings on different substrates with Al1 − xMnxN, Al1 − xCoxN (x = 2–7 at%) and Al1 − xCrxN with higher Cr contents (x = 4–7%) are underway. Investigations of the magnetic properties of the coatings at temperatures up to the Curie point are also in progress.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005853/abstract [article] Depletion sensor for protective high temperature coatings [texte imprimé] / K. Aleksandrov, Auteur ; M. Schutze, Auteur ; I. Teliban, Auteur . - 2011 . - pp. 706–712.
Génie Mécanique
Langues : Anglais (eng)
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 706–712
Mots-clés : Alloy depletion Magnetic phases Pack cementation Protective coatings Sputtering Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : In order to minimise corrosion at high temperatures metallic or intermetallic Al- and/or Cr-rich protective coatings are applied to metallic alloys. Protection against corrosion is achieved by the formation of a continuous Al2O3 and/or Cr2O3 layer. Progressive scale formation, as well as interdiffusion between the coating and the substrate during long operating stages depletes the scale-forming elements, Al and Cr. The decrease of their concentration below a critical value is followed by accelerated corrosion and rapid breakdown of the component. Non-destructive depletion measurement is not possible, because of the absence of suitable materials that serve simultaneously as depletion sensors and reservoir phases. In a novel development, protective high temperature coatings containing a magnetic phase which at the same time acts as a reservoir phase are used as a depletion sensor. The alloy surface is coated with the magnetic substance either by reactive magnetron co-sputtering or by using pack cementation. In the course of operation, the formation of a protective oxide scale depletes the reservoir and the measured magnetic signal decreases. Measurement of the change of the coating's magnetic signal enables in situ assessment and non-destructive detection of depletion. In order to avoid perturbances in the magnetic signal coming from the coating the metallic substrate must be non-magnetic. Therefore this concept is restricted to Cr/Ni-austenitic steels and Ni-base alloys. Doping of AlN with transition metals (Al1 − xMexN, Me = Cr, Co, Mn, x = 2–7 at%) makes it a suitable magnetic reservoir phase, i.e. Al- and/or Cr-containing. Furthermore, it is ferromagnetic, has a high Curie temperature and is magnetically soft. Samples of Alloy 800 and Alloy 602 CA were coated with Al1 − xCrxN (x = 2 and 3 at%) using both pack cementation and PVD. Measurements of the magnetic moments of the coatings at temperatures up to 300 °C show very soft ferromagnetic behaviour. Coatings on different substrates with Al1 − xMnxN, Al1 − xCoxN (x = 2–7 at%) and Al1 − xCrxN with higher Cr contents (x = 4–7%) are underway. Investigations of the magnetic properties of the coatings at temperatures up to the Curie point are also in progress.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005853/abstract
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 713–716
Titre : Measurements of fluorine depth-profiles on TiAl turbine blades using ion beam analytical techniques Type de document : texte imprimé Auteurs : S. Neve, Auteur ; P. J. Masset, Auteur ; H.-E. Zschau, Auteur Année de publication : 2011 Article en page(s) : pp. 713–716 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Halogen-effect PIGE RBS TiAl Titanium aluminides Turbine blade Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Intermetallic TiAl alloys are foreseen to substitute Ni-based alloys in several high-temperature applications such as turbine blades for aeronautics. Because of their low density the mass of these components could be reduced by half. However, a mixed oxide scale of TiO2 and Al2O3 which provides no oxidation protection is growing at temperatures above 700 °C. By means of the halogen-effect the high-temperature oxidation resistance of TiAl alloys can be improved by orders of magnitude. Therefore fluorine was introduced into turbine blades using two different chemical fluorination methods. The application of a fluorine treatment promotes the growth of a pure and dense alumina scale which prevents the alloy from increased oxidation. In previous work it has been shown that an appropriate fluorine content after oxidation and its location beneath the surface are indicators of a successful fluorine effect. In the present work, the fluorine content was measured before and after oxidation of TNB alloy as a function of depth by using proton induced gamma-ray emission (PIGE) in a specially designed vacuum chamber at the 2.5 MV van-de-Graaff accelerator at the IKF. Additionally, composition and thickness of the oxide scale was determined by Rutherford backscattering spectrometry (RBS). The ion beam techniques are non-destructive and thus offer a method for quality assurance of the halogen treatment.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005886/abstract [article] Measurements of fluorine depth-profiles on TiAl turbine blades using ion beam analytical techniques [texte imprimé] / S. Neve, Auteur ; P. J. Masset, Auteur ; H.-E. Zschau, Auteur . - 2011 . - pp. 713–716.
Génie Mécanique
Langues : Anglais (eng)
in Materials and corrosion > Vol. 62 N° 7 (Juillet 2011) . - pp. 713–716
Mots-clés : Halogen-effect PIGE RBS TiAl Titanium aluminides Turbine blade Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Intermetallic TiAl alloys are foreseen to substitute Ni-based alloys in several high-temperature applications such as turbine blades for aeronautics. Because of their low density the mass of these components could be reduced by half. However, a mixed oxide scale of TiO2 and Al2O3 which provides no oxidation protection is growing at temperatures above 700 °C. By means of the halogen-effect the high-temperature oxidation resistance of TiAl alloys can be improved by orders of magnitude. Therefore fluorine was introduced into turbine blades using two different chemical fluorination methods. The application of a fluorine treatment promotes the growth of a pure and dense alumina scale which prevents the alloy from increased oxidation. In previous work it has been shown that an appropriate fluorine content after oxidation and its location beneath the surface are indicators of a successful fluorine effect. In the present work, the fluorine content was measured before and after oxidation of TNB alloy as a function of depth by using proton induced gamma-ray emission (PIGE) in a specially designed vacuum chamber at the 2.5 MV van-de-Graaff accelerator at the IKF. Additionally, composition and thickness of the oxide scale was determined by Rutherford backscattering spectrometry (RBS). The ion beam techniques are non-destructive and thus offer a method for quality assurance of the halogen treatment.
DEWEY : 620.1 ISSN : 0947-5117 En ligne : http://onlinelibrary.wiley.com/doi/10.1002/maco.201005886/abstract
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