抄録
The paper consists of two parts. In part I, the disorder-order transformation of AB type superlattice was studied by postulating an elementary mechanism of atomic diffusion through vacancy, that is, the exchange of a vacancy and its neighbouring atom. The height of potential for the atomic migration was assumed to be a constant plus nearest neighbour energies of the atom. The kinetics of the ordering was treated in an approximation which is equivalent to the well known. Bethe Peierls’ approximation. This is described by five differential equations to determine five time dependent variables, three of which are concerned with vacancies. By solving these equations, it was shown that if an AB type alloy is quenched from a high temperature disordered state to a temperature somewhat below the critical temperature, and then annealed at that temperature, the following disorder-order transformation will exhibit a multiple-step character. In part II, this prediction was compared with the experimental results of Ni3Fe. It was found that the theory can describe at least qualitatively, each of the observed four stages of the disorder-order transformation at 490°C of this alloy. Namely, the first stage is the abrupt change in the state of imperfections, the second, the development of short range order without long range order, the third, the cooperative formation of long range order, and the fourth, the process to complete its long range order against the retarding effect of antiphase and imperfections.
