DEFORMATION-BEHAVIOR 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 degrees C w here a significant yield drop occurred to 150 MPa at 1550 degrees C, w here a creep-type response was obtained, with an apparent change in th e slope of the sigma(y) versus T plot close to 1400 degrees C. The def ormation microstructures observed using transmission electron microsco py were dominated by twins up to 1400 degrees C, whereas at higher tem peratures the deformation appeared to proceed by a mixture of twinning and slip. In all cases the twins appeared on a single composition pla ne within each grain and this could be due to an autocatalytic nucleat ion effect. This microstructure may be related to the onset of brittle behaviour at a temperature where residual components of the imposed s train cannot be compensated for by the activation of other deformation modes. (C) 1997 Elsevier Science S.A.