Strain-Rate Sensitivity and Failure Peculiarities in Compression of the Nanocrystalline Ni-20 Pct Fe Alloy at Low Temperatures

Abstract

The strain-rate sensitivity of the applied stress was measured, and the values of the activation volume of the process of the plastic deformation V along the deformation curve in compression of the nanocrystalline (NC) Ni-20 pct Fe alloy (with average grain size ~22 nm) in the temperature range of 300 to 77 K (27 to −196 °C) were calculated. It was found that the decrease of the temperature from 300 to 77 K leads to a decrease of the value of V from 20 to 8 b3, and values of V do not depend on the strain. Fractographic features of the failure surfaces were studied in the temperature range 300 to 4.2 K (27 to −269 °C). Observed traces of melting on these surfaces at temperatures below 300 K indicate the intense heating in the catastrophic shear band of the alloy in the moment of failure. Causes of low-temperature decohesion along grain boundaries are discussed in terms of the sulfur segregation influence.