Micropillar compression of hexagonal and cubic NbCo2 Laves phases

Conference Dates

October 1-6, 2017


Transition metal-based Laves phases have high strength and good creep resistance which make them potential candidates for high-temperature applications. On the other hand, they exhibit pronounced brittleness at low temperature. Due to their brittleness, the difficulty of producing sufficiently large and flaw-less bulk samples for conventional mechanical testing limits the study of their mechanical properties. Therefore, today there is only very little knowledge on their mechanical behavior and their deformation mechanism. The existing literature indicates that the mechanical properties of transition metal-based Laves phases significantly depend on their composition. The underlying mechanism is not yet understood.

Laves phases with AB2 stoichiometry may have three structure types, cubic C15 (MgCu2-type), hexagonal C14 (MgZn2-type) and hexagonal C36 (MgNi2-type). All three types of Laves phases exist as stable phases in the Co-Nb system and the C15-NbCo2 Laves phase has a large composition range of 26.0±0.5 − 35.3±0.3 at.% Nb. It makes the NbCo2 Laves phases a perfect candidate to study not only the deformation behavior of transition metal-based Laves phases but also the influence of composition and crystal structure on their strength. To circumvent the difficulties in preparing large flaw-less samples, we grew the NbCo2 Laves phases with diffusion couples and studied their mechanical properties by micropillar compression tests. After proper heat treatment, extended diffusion layers of the three NbCo2 Laves phases with coarse grains were obtained. As there are concentration gradients in the diffusion layers, micropillars with different compositions can be obtained by focused ion beam (FIB) milling at selected positions in the diffusion layers.

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