PLASTICITY OF COLUMNAR-GRAINED COSI2 WITH THE C1 STRUCTURE

Columnar-grained CoSi2 crystals with the C1 structure (CaF2 type) have been deformed in compression in vacuum at high temperatures up to 1400 K. The yield stress increases steeply with decreasing temperature, and the fracture precedes yielding below 700 K. Above 900 K, specimens can be compressed to a strain above 80% without fracture. From the strain-rate sensitivity determined by the stress relaxation test and the temperature dependence of the yield stress, the activation volume and the activation enthalpy of plastic deformation have been analysed. The activation volumes at high stresses (tau* > 100 MN m-2) are less than 10b3 (where b is the magnitude of the Burgers vector), indicating that the deformation is controlled by the Peierls mechanism. The total activation enthalpy is about 3 eV. The possibility of the dissociation of 1/2 < 110 > dislocations is proposed.