A theoretical model of internal stress superplasticity is developed in a si
ngle-phase polycrystalline material with an anisotropic thermal expansion.
Quasi-steady state creep equation during a thermal cycle is derived quantit
atively based on continuum micromechanics. The model assumes that the gener
ated mismatch strain is accommodated simultaneously by the plastic flow of
the material. The linear creep deformation. which corresponds to internal s
tress superplasticity, is obtained at low applied stress region. and the cr
eep rate depends on the crystallographic texture of the material. The valid
ity of the model is experimentally verified using polycrystalline zinc whic
h is a typical metal having large anisotropy in thermal expansion. The calc
ulated strain rates using the texture information and the isothermal creep
equation agree quantitatively well with the experimental results. The appar
ent activation energy of thermal cycling creep reveals 1/n (n: stress expon
ent of isothermal creep) of that of isothermal creep, which is one of the c
haracteristics of internal stress superplasticity. Except for the factors a
ttributable to the material geometry, the thermal cycling creep equation in
the polycrystalline material is identical to that in a metal matrix compos
ite. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All r
ights reserved.