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Intergranular crack tip oxidation in a Ni-base superalloy

Leif Viskari (Institutionen för teknisk fysik, Materialens mikrostruktur ) ; Magnus Hörnqvist (Institutionen för teknisk fysik, Materialens mikrostruktur ) ; K. L. Moore ; Yu Cao (Institutionen för material- och tillverkningsteknik, Yt- och mikrostrukturteknik) ; Krystyna Stiller (Institutionen för teknisk fysik, Materialens mikrostruktur )
Acta Materialia (1359-6454). Vol. 61 (2013), 10, p. 3630-3639.
[Artikel, refereegranskad vetenskaplig]

High-temperature intergranular crack tip oxidation under a single 600 s long sustained tensile load at 700 degrees C was studied for the Ni-base superalloy Allvac 718Plus. High-resolution analytical techniques showed oxidation to take place at and immediately ahead of the tip of an open crack, forming a closed but layered oxide structure about the prior (now oxidized) grain boundary. Near the prior grain boundary the oxide is Ni-rich, with a Co-enriched layer furthest away from the metal and a Fe-enriched region below this. A Cr-rich oxide is present below the outer Ni-rich oxides throughout the crack, also in the direction of crack growth. This is believed to have a hindering effect on oxidation ahead of the crack. Ni-3(Nb,Al) gamma' precipitates close to the grain boundaries were found to oxidize and form regions of near-stoichiometric NiO within the oxide layers. Remaining constituents of gamma' (e.g. Al and Nb) were found to be enriched in the surrounding oxidized matrix and also to produce thin oxide layers near the interface between the unoxidized metal and the Cr-rich oxide. The formation of the crack tip oxides is discussed with regard to thermodynamics, kinetics and the influence of applied mechanical load.

Nyckelord: Oxygen, Diffusion, Atom probe tomography, Transmission electron microscopy, Secondary ion mass, atom-probe tomography, nickel-based superalloy, high-temperature, growth-behavior, alloy 718, fatigue, embrittlement, microstructure, propagation, mechanisms

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Denna post skapades 2013-07-19. Senast ändrad 2017-03-02.
CPL Pubid: 180212


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Institutioner (Chalmers)

Institutionen för teknisk fysik, Materialens mikrostruktur (2012-2015)
Institutionen för material- och tillverkningsteknik, Yt- och mikrostrukturteknik (2005-2017)



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Oxygen Induced High Temperature Crack Growth in Ni-base Superalloys