Grain boundary microstructure and fatigue crack growth in Allvac 718Plus superalloy
Journal article, 2011

The correlation between grain boundary microstructure and fatigue crack growth with hold-times was investigated for two conditions of the superalloy Allvac 718Plus; a Standard condition with the recommended distribution of grain boundary phases and a Clean condition with virtually no grain boundary phases. Fatigue testing was performed at 704 degrees C using 10 Hz cyclic load with intermittent hold-times of 100 s at maximum tensile load. Microstructural characterization and fractography were conducted using scanning- and transmission electron microscopy techniques. Auger electron- and X-ray photoelectron spectroscopy techniques were used for oxide analyses on fracture surfaces. It was found that in the Standard condition crack growth is mostly transgranular for 10 Hz loading and intergranular for hold-times, while for the Clean condition crack growth is intergranular in both load modes. The lower hold-time crack growth rates in the Standard condition are attributed to grain boundary delta-phase precipitates. No effect of delta-phase was observed for 10 Hz cyclic loading crack growth rates. Two different types of oxides and oxide colours were found on the fracture surfaces in the Standard condition and could be correlated to the different loading modes. For cyclic loading a bright thin Cr-enriched oxide was dominate and for hold-times a dark and slightly thicker Nb-enriched oxide was dominant These oxide types could be related to the oxidation of delta-phase and the matrix respectively. The influence of delta-phase precipitates on crack propagation is discussed.

Delta-phase

Electron

Hold-time fatigue

microscopy

Auger electron spectroscopy

Oxidation

X-ray photoelectron spectroscopy

Fractography

Author

Leif Viskari

Chalmers, Applied Physics, Microscopy and Microanalysis

Yu Cao

Chalmers, Materials and Manufacturing Technology, Surface and Microstructure Engineering

Mats Norell

Chalmers, Materials and Manufacturing Technology, Surface and Microstructure Engineering

Göran Sjöberg

Volvo Group

Krystyna Marta Stiller

Chalmers, Applied Physics, Microscopy and Microanalysis

Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing

0921-5093 (ISSN)

Vol. 528 6 2570-2580

Subject Categories

Materials Engineering

Areas of Advance

Materials Science

DOI

10.1016/j.msea.2010.11.080

More information

Latest update

11/26/2018