Documents disponibles écrits par cet auteur

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