抄録
The superlattice formation of Ni3Fe in steady temperature annealings (at 500°C, 480°C and 460°C) was studied by direct observation of the heat of evolution and by measurement of specific heat on heating after each treatment. The multiple-step character of formation process of this superlattice disappeared gradually by lowering the temperature of anneal. All results are plotted on the same internal energy-temperature plane. The diagram is well explained by our theoretical treatment of the process which divides the process into two steps, with and without the long range order. But there was found a process of the third type, which remains after the second process has been completed. This becomes more distinct when the annealing temperature is lowered. For instance, when the disordered specimen was rapidly cooled to 460°C, and annealed at this temperature, it was observed that the development of order looks as though it reaches an apparent saturation after about 80 hours annealing. But, measurements of specific heat on heating of the corresponding specimen showed that the internal energy of the specimen is about 170 cal/atom higher than that of true equilibrium state at 460°C. This type of process, which has a relaxation time of the order of a month, will presumably be related to the antiphase problem. The nucleation and antiphase problems in superlattice are also discussed. The specimen which was quenched from 700°C shows an anomalous generation of heats between 230°C and 420°C on heating. This will be an important phenomenon for the formation process of this superlattice.
