Deformation Behaviour in Ni3Ge Single Crystals Containing 76 at%Ni

In order to make a comparison of the plastic behaviour between Ni3Al and Ni3Ge, where Al is a 3B and Ge a 4B-subgroup element, effects of temperature, orientation and strain-rate on the temperature dependence of strength are investigated in Ni3Ge single crystals with 76 at%Ni. It is found that at 77 K there is an appreciable orientation dependence in compressive 0.2% flow stress. For orientation near [\bar111], the onset of cube slip is found to occur at as low as ambient temperature which is unusual for the L12 single crystals. The thermal component of critical resolved shear stress for the cube slip vanishes also at a much lower temperature and the athermal component is found to exhibit a slight negative temperature dependence arising from the temperature dependence of shear modulus. For orientation near [001] and at the temperatures above the peak, the characteristic yield drop and the following steady-state deformation are found as in other L12 intermetallic compounds. The activation energy for the steady-state deformation is found to be 277 kJ/mol which is reasonably in good agreement with the value for the diffusion of Ge in Ni3Ge