In situ micro-cantilever tests to study fracture properties of NiAl single crystals

• Published in: Acta materialia 2012-02, Vol.60 (3), p.1193-1200
• Main Authors: Iqbal, F., Ast, J., Göken, M., Durst, K.
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Fracture toughness; Fractures; In situ micro-cantilever testing; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; NiAl; Strain gradients
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2011.10.060

In situ micro-cantilever tests were carried out to determine the anisotropic fracture toughness of NiAl single crystals. Notched micro-cantilever beams with a beam length of 8μm, 1.5μm thickness and 1.8μm width were milled in so-called “hard” and “soft” orientations of NiAl using a focused ion beam. These cantilevers were loaded in situ with the help of a cantilever-based nanoindenter mounted inside a scanning electron microscope. A fracture toughness of 3.52±0.29MPam1/2 was obtained for the “soft” orientation and 5.12±0.50MPam1/2 for the “hard” orientation, which is in good agreement with literature values on the fracture toughness of macroscopic NiAl specimens. Furthermore, nanoindentations were performed for studying the size effects occurring at small length scales for both orientations. The applicability of the small sample geometries for testing the fracture toughness is finally discussed in terms of size effects in the flow stress of the material due to dislocation nucleation and strain gradients at the crack tip.