UNIFIED INTERPRETATION OF INTERNAL STRESS SUPERPLASTICITY MODELS BASED ON THERMALLY- ACTIVATED KINETICS

摘要

Three main theoretical models of internal stress superplasticity proposed by Greenwood and Johnson [Proc. R. Soc. A, 1965, 283, 403], Sherby el al. [Maler. Sci. Teclhnol., 1985, 1, 925], and Sato and Kuribayashi [Acta metall. mater., 1993, 41, 1759] have been expanded to include the temperature depen- dence of the average strain rate. It is revealed that the constitutive equations of these models are equivalent regarding the thermally activated kinetics, and that the apparent activation energy of internal stress super- plasticity is equal to l (where n is the stress exponent of isothermal power-law creep) times that of iso- thermal power-law creep. This theoretical prediction has been experimentally verified by the thermal cycling creep tests using the same temperature profiles with several equivalent temperatures in a Be par- ticle-dispersed Al matrix composite. The obtained apparent activation energy was 22 kJ/mol, which is ap- proximately l.'7 times that of isothermal creep.