During superplastic deformation, grain growth occurs more rapidly than without deformation, which can be divided into two components, the deformation induced (∂\barD⁄∂ε)_t and the static (∂\barD⁄∂t)_ε . In the present study, a method to separate these components is developed analytically. The former can be evaluated approximately by (\barD⁄\barD_s), where \barD and \barD_s are grain sizes after deformation and after the equivalent annealing without deformation, respectively. The deformation induced component causes flow hardening presented by the flow hardening parameter γ=mp(∂ln\barD⁄∂ε)_t, where the constitutive equation is expressed as \dotε=K\barD^−pσ^1⁄m. Flow hardening stabilizes the deformation itself alike the work hardening at the ambient temperature.
The method to separate these two components is confirmed experimentally using microduplex Zn-22%Al alloy. In the superplastic deformation region, the deformation induced component is independent of strain rate, deformation temperature and initial grain size, as well as the magnitude of the static grain growth. Besides, it is indicated by ln(\barD⁄\barD_s)=αε, where α\simeq0.3. The observed increase of flow stress under the constant strain rate tests can be ascribed to the whole grain growth.