Deformation behaviour of the C15 Laves phase Cr2Nb

Compression tests have been used to show the temperature dependence of the deformation behaviour for stoichiometric samples of the C15 Laves phase Cr2Nb. The yield stress varied from 550 MPa at 1300 C where a significant yield drop occurred to 150 MPa at 1550 C, where a creep-type response was obtained, with an apparent change in the slope of the σy versus T plot close to 1400 C. The deformation microstructures observed using transmission electron microscopy were dominated by twins up to 1400 C, whereas at higher temperatures the deformation appeared to proceed by a mixture of twinning and slip. In all cases the twins appeared on a single composition plane within each grain and this could be due to an autocatalytic nucleation effect. This microstructure may be related to the onset of brittle behaviour at a temperature where residual components of the imposed strain cannot be compensated for by the activation of other deformation modes. (orig.)