Intergranular crack tip oxidation in a Ni-base superalloy
Journal article, 2013

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.

Transmission electron microscopy

atom-probe tomography

nickel-based superalloy

mechanisms

high-temperature

Secondary ion mass

Oxygen

propagation

embrittlement

alloy 718

growth-behavior

Atom probe tomography

fatigue

Diffusion

microstructure

Author

Leif Viskari

Chalmers, Applied Physics, Materials Microstructure

Magnus Hörnqvist

Chalmers, Applied Physics, Materials Microstructure

K. L. Moore

University of Oxford

Yu Cao

Chalmers, Materials and Manufacturing Technology, Surface and Microstructure Engineering

Krystyna Marta Stiller

Chalmers, Applied Physics, Materials Microstructure

Acta Materialia

1359-6454 (ISSN)

Vol. 61 10 3630-3639

Subject Categories

Materials Engineering

Areas of Advance

Materials Science

DOI

10.1016/j.actamat.2013.02.050

More information

Latest update

10/15/2018