Universality of the Phenomenology of Structural Superplasticity

Abstract:

The equation σ=Kέ^m, where σ is the applied stress, έ is the strain rate, K and m are material constants that depend on stress / strain rate, temperature and grain size is often used to describe structural superplasticity. The general shape of the logσ-logέ curve is sigmoidal. Based on limited data, it was suggested by us earlier that a universal σ-έ curve could exist in a properly normalized space. έ and m are normalized with respect to έ_opt and m_max, the strain rate at which m is a maximum and the maximum m value respectively. Here a multi-dimensional relationship involving σ/σ_opt-έ/έ_opt-m/m_max-ΔF₀/kT-η/η_opt is developed; σ_opt corresponds to έ_opt, ΔF₀ is the free energy of activation for the rate controlling mechanism, k the Boltzmann constant, T the absolute test temperature, η the (apparent) viscosity of the superplastic alloy and η_opt is the viscosity of the same alloy for m=1 in a dimensionless σ-έ space. Using data concerning many systems, the phenomenology of structural superplasticity in all classes of materials is shown to be unique.

• Periodical: Materials Science Forum (Volumes 838-839)
• Pages: 84-88
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.838-839.84
• Online since: January 2016
• Authors: Sriharsha Sripathi*, Anantha Padmanabhan
• Keywords: Activation Energy, Optimal Strain Rate, Strain Rate Sensitivity, Structural Superplasticity, Universal Superplasticity Curve, Viscosity

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