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Fracture toughness evaluation of NiAl single crystals by microcantilevers—a new continuous J-integral method

Ast, Johannes and Merle, Benoit and Durst, Karsten and Göken, Mathias (2016):
Fracture toughness evaluation of NiAl single crystals by microcantilevers—a new continuous J-integral method.
In: Journal of Materials Research, Cambridge University Press, New York, NY, USA, pp. 3786-3794, 31, (23), ISSN 0884-2914, DOI: 10.1557/jmr.2016.393, [Online-Edition: https://doi.org/10.1557/jmr.2016.393],
[Article]

Abstract

The fracture toughness of NiAl single crystals is evaluated with a new method based on the J-integral concept. The new technique allows the measurement of continuous crack resistance curves at the microscale by continuously recording the stiffness of the microcantilevers with a nanoindenter. The experimental procedure allows the determination of the fracture toughness directly at the onset of stable crack growth. Experiments were performed on notched microcantilevers which were prepared by focused ion beam milling from NiAl single crystals. Stoichiometric NiAl crystals and NiAl crystals containing 0.14 wt% Fe were investigated in the so-called "hard" orientation. The fracture toughness was evaluated to be 6.4 +/- 0.5 MPa m(1/2) for the stoichiometric sample and 7.1 +/- 0.5 MPa m(1/2) for the iron containing sample, indicating that the addition of iron enhances the ductility. This effect is intensified with ongoing crack propagation where the Fe-containing sample exhibits a stronger crack resistance behavior than the stoichiometric NiAl single crystal. These findings are in good agreement with macroscopic fracture toughness measurements, and validate the new micromechanical testing approach.

Item Type: Article
Erschienen: 2016
Creators: Ast, Johannes and Merle, Benoit and Durst, Karsten and Göken, Mathias
Title: Fracture toughness evaluation of NiAl single crystals by microcantilevers—a new continuous J-integral method
Language: English
Abstract:

The fracture toughness of NiAl single crystals is evaluated with a new method based on the J-integral concept. The new technique allows the measurement of continuous crack resistance curves at the microscale by continuously recording the stiffness of the microcantilevers with a nanoindenter. The experimental procedure allows the determination of the fracture toughness directly at the onset of stable crack growth. Experiments were performed on notched microcantilevers which were prepared by focused ion beam milling from NiAl single crystals. Stoichiometric NiAl crystals and NiAl crystals containing 0.14 wt% Fe were investigated in the so-called "hard" orientation. The fracture toughness was evaluated to be 6.4 +/- 0.5 MPa m(1/2) for the stoichiometric sample and 7.1 +/- 0.5 MPa m(1/2) for the iron containing sample, indicating that the addition of iron enhances the ductility. This effect is intensified with ongoing crack propagation where the Fe-containing sample exhibits a stronger crack resistance behavior than the stoichiometric NiAl single crystal. These findings are in good agreement with macroscopic fracture toughness measurements, and validate the new micromechanical testing approach.

Journal or Publication Title: Journal of Materials Research
Volume: 31
Number: 23
Publisher: Cambridge University Press, New York, NY, USA
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Physical Metallurgy
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences
Date Deposited: 27 Nov 2017 11:48
DOI: 10.1557/jmr.2016.393
Official URL: https://doi.org/10.1557/jmr.2016.393
Funders: The authors gratefully acknowledge the funding of the German Research Council (DFG), which within the framework of its 'Excellence Initiative' supports the cluster of Excellence 'Engineering of Advanced Materials' at the University of Erlangen-Nurnberg.
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