Deformation mechanisms in Cr20Ni80 alloy at elevated temperatures

The mechanisms of plastic deformation of Cr20Ni80 nichrome with an initial grain size of 80 μm were studied in the temperature range 600–950°C and the strain-rate range 1.5 × 10^?6?5 × 10^?2s^?1. Nichrome is shown to exhibit anomalously high values of stress exponent n and a high deformation activation energy Q. These unusual properties were found to be caused by “threshold” stresses below which deformation does not occur. An analysis of the deformation behavior with allowance for threshold stresses reveals the regions of hot, warm, and cold deformation in nichrome. At normalized strain rates (dot varepsilon ) kT/D _{1 Gb} < 10^?8, the true values of n and Q are ～4 and 285 ± 30 kJ/mol, respectively. In the normalized-strain range 10^?8?10^?4 n ～ 6 and the deformation activation energy decreases to 175 ± 30 kJ/mol. This change in the deformation-behavior characteristics is explained by the transition from high-temperature dislocation climb, which is controlled by lattice self-diffusion, to low-temperature dislocation climb, which is controlled by pipe diffusion, as the temperature decreases. At (dot varepsilon ) kT/D _{1 Gb} = 10^?4, a power law break-down takes place and an exponential law (which describes the deformation behavior in the range of cold deformation) becomes operative.