Stability of an Ordered phase under Rapid Heating

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Down quenching in a common operation employed in materials science and technology communities both to investigate the kinetics of phone transition and to realize new structural and functional properties. In the present study, we focused on the reverse operation, namely the up-quenching operation, and we attempted to clarify the stability and phase transition kinetics of a low temperature ordered phone both theoretically and experimentally. Particular focuses were placed on ; (1) phase transition behavior below an above the spinodal disordering temperature, and (2) detection and interpretation of Retro effect. We first performed the theoretical calculations based on Cluster Variation Method and Path Probability Method and suggested that the spinodal disordering in a common phenomenon for an order-disorder system of first-order transition. Further theoretical studies based on the Phase Field Method clarified the microstructural evolution kinetics of Anti phase boundary during the relaxation process, and by combining with the FLAPW electronic structure calculations, more realistic calculations for the microstructural topology of Anti Phase boundary was performed for Fe-Pd system. The present experimental investigations are classified into two major categories. One is the detection of spinodal disordering temperature for Ni-Mo system and the other is the clarification of the mechanism of Retro effect for Cu-Au system. For the former, anomaly was detected for both the electrical resistivity and the coefficient of thermal expansion when the heating rate is accelerated. For the latter, combined with Laser Microscopy, the evolution and devolution of the surface morphology is carefully observed upon heating and cooling. We concluded that the Retro effect is associated with internal stresses originated from the constraint due to the discontinuity of grain boundaries.