Cyclic deformation behaviour of Ni3Ge single crystals at room temperature

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Abstract
Fully reversed strain-controlled tension-compression tests have been performed at room temperature to study cyclic deformation properties of Ni3Ge single crystals. The cyclic deformation was performed with the stress axis parallel to the [245] direction at a strain rate of 1·0 × 10−45−1 and at a total strain amplitude between 5·0×10−4 and 1·5 × 10−3. Cyclic strain-hardening occurred to saturation over the range of the employed strain amplitudes. The cyclic stress amplitude was found to be higher in compression than in tension at a plastic strain amplitude larger than 1×10−5, where mew dislocations are operative. This stress asymmetry became more prominent (i.e. the mean stress amplitude became larger in magnitude) as the plastic strain amplitude became larger. At a plastic strain amplitude less than 1 ×10 −5, where edge dislocations are operative. the stress amplitude was found to be symmetric. A similar stress asymmetry was also observed for monotonic flow stress. The cyclic hardening is explained by considering an interaction between the screw dislocations.