Crystallization kinetics and stress induced twinning/de-twinning

September 24, 2010

[1] Nucleation, growth and impingement modes deduced from isothermally and isochronally conducted phase transformations: Calorimetric analysis of the crystallization of amorphous Zr50Al10Ni40

F Liu et al

The crystallization kinetics of amorphous Zr50Al10Ni40, as measured by means of both isothermal and isochronal differential scanning calorimetry, were evaluated using a new procedure involving application of a modular analytical model to provide a complete description of the phase-transformation kinetics, in combination with a preceding analysis of the transformation-rate maximum. The power of detailed analysis of the position of the transformation-rate maximum, as a function of the transformed fraction, was demonstrated by identification of the operating impingement mode. On this basis, the kinetic parameters governing the crystallization kinetics could then be determined quantitatively using the modular analytical model. The crystallization governing mechanisms could be varied by appropriate control of the crystallization conditions. The results obtained are consistent with the microstructural evolution, as observed by transmission electron microscopy.

[2] Simulations of stress-induced twinning and de-twinning: A phase field model

S Hu et al

Twinning in certain metals or under certain conditions is a major plastic deformation mode. Here we present a phase field model to describe twin formation and evolution in a polycrystalline fcc metal under loading and unloading. The model assumes that twin nucleation, growth and de-twinning is a process of partial dislocation nucleation and slip on successive habit planes. Stacking fault energies, energy pathways (γ surfaces), critical shear stresses for the formation of stacking faults and dislocation core energies are used to construct the thermodynamic model. The simulation results demonstrate that the model is able to predict the nucleation of twins and partial dislocations, as well as the morphology of the twin nuclei, and to reasonably describe twin growth and interaction. The twin microstructures at grain boundaries are in agreement with experimental observation. It was found that de-twinning occurs during unloading in the simulations, however, a strong dependence of twin structure evolution on loading history was observed.

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