Analysis of cyclic plastic response of nickel based IN738LC superalloy

Cyclic strain controlled tests with blocks of stepwise increasing strain amplitudes were applied to cylindrical specimens of cast Inconel 738LC superalloy at 23 and 800°C in laboratory atmosphere. Cyclic hardening/softening curves and shortened cyclic stress–strain curves were obtained at both temperatures. The hysteresis loops were analyzed using generalized statistical theory of the hysteresis loop. The second derivative of the half-loop exhibits three domains. The initial drop represents the plastic strain relaxation under decreasing effective stress and two peaks correspond to the probability density distribution of the internal critical stresses in matrix (γ phase) and γ′ phase respectively. Localized cyclic straining was identified using dislocation structure of PSBs and surface relief corresponding to PSMs. Weibull probability density function was fitted to individual peaks and effective stress component and probability density distributions of the internal critical stresses were quantitatively evaluated.