Experimental study and comparable analysis of plasticity of the Ni-18.75 at.% Fe alloy in coarse grained and nanocrystalline states in the temperature range 4.2₃50 K

The mechanical properties of the coarse grained (CG) Ni-18.75 at.% Fe alloy (the average grain size is 35 mkm) were studied in uniaxial compression with a constant rate in the temperature range 4.2-350 K. The temperature dependence of yield stress was measured, and the shape of the stress-strain curves was analyzed. The temperature dependences of flow stress, strain rate sensitivity of flow stress and activation volume of plastic deformation were measured for plastic strain of 2 %. The thermal activation analysis of the experimental data was carried out. It is shown that the plastic deformation of coarse grained alloy in the temperature range 35-350 K has a thermally activated type and it is controlled by the single deformation mechanism. Empirical estimates of the parameters of dislocation interaction with local barriers and the values of effective and internal stresses were obtained. The comparable analysis was carried out of the regularities of the low-temperature thermally activated plastic deformation of the alloy in CG and nanocrystalline (NC) states. It is concluded that the microscopic barriers, controlling the thermally activated plastic flow, are different in NC and CG states. The range of local barriers, which can determine the thermally activated dis-location plasticity in NC and CG states, is discussed.