Documents disponibles écrits par cet auteur

Combined Al- plus F-treatment of Ti-alloys for improved behaviour at elevated temperatures / A. Donchev in Materials and corrosion, Vol. 62 N° 7 (Juillet 2011) 

Public ISBD [article]  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

Depletion sensor for protective high temperature coatings / K. Aleksandrov in Materials and corrosion, Vol. 62 N° 7 (Juillet 2011) 

Public ISBD [article]  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

Oxidation protection of Ni-base superalloys by halogen treatment / H.-E. Zschau in Materials and corrosion, Vol. 62 N° 7 (Juillet 2011) 

Public ISBD [article]  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