New kinetic model for primary recrystallization of pure metals

In recrystallization experiments on pure metals, quite often the transformation rate observed at higher fractions transformed is distinctly smaller than predicted by the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model.^[1,2,3] Stimulated by recent experimental results, two important changes to the model are suggested: a nucleation rate related to the size of the interfacial area “recrystallized-deformed” present and an exponentially decreasing growth rate for each grain. The modified model still yields a sigmoidal curve for the fraction recrystallized. Yet, plotted in order to determine the Avrami exponent, it shows a very similar deviation as that found in experimental results. Further, it will be discussed how the dependence of the recrystallization process on temperature and magnitude of deformation can be incorporated into the model and what the physical reason for the slowing down of the growth rates of the individual grains might be.     

A theoretical model for the elevated temperature deformation of dispersion hardened metals

A theoretical model is presented to describe the elevated temperature (above 1/2T_m @#@) deforma-tion of dispersion hardened metals such as TD-nickel and SAP alloys. The model is based on two proposals: 1) Both dislocation glide and climb are influenced by matrix stresses at small, incoherent, second phase dispersed particles produced by surface tension effects at the particle-matrix interface. 2) Two concurrent processes may contribute to the elevated temperature deformation of polycrystalline dispersion hardened metals, dislocation motion and diffusion controlled grain boundary sliding. The model may explain the origins of high apparent activation enthalpies and large stress sensitivities which have been observed in dispersion hardened metals. It may also provide guidelines for optimization of elevated temperature strength.