Study of the superplasticity of inconel 718 using tests with cyclic perturbation of strain rate

Abstract

The imposition of a sinusoidal perturbation of variable frequency to the strain rate of a material subjected to a monotonic tensile test is an easy technique to study the kinetics of plastic deformation that has been scarcely used. The application of this technique to an Inconel 718 in its superplastic regime allows for obtaining has permitted to obtain the value of the instantaneous strain rate sensitivity, m, in a continuous way as deformation. It is then possible a more complete characterization than that offered by conventional techniques, where strain rate sensitivity is obtained from the response to several instantaneous strain rate changes. The proposed method has revealed the influence that the time derivative of strain rate, e, has on the value of m. For a comparison of the rexults of both types of measurement, tests with sinusoidal perturbation and with instantaneous strain rate changes have been performed. The temperature and strain rate ranges studied span from 925 C to 1000 C and from 10 -4 s -1 to 10 -2 s -1 . The dynamic response of the system has been analyzed too in terms of amplitude and phase shift of the resulting stress signal response to the imposed sinusoidal perturbation of strain rate.