The non-equilibrium phase transition theory of martensitic transformation

Abstract

A new triggering model of the martensitic transformation is presented. In this model martensitic transformation is thought to be triggered by coherent phonons, the ordering phonons emitted by a simulated emission process of phonons called the potential emission of coherent phonons attained by quenching. The thermodynamic basis of the present model is discussed briefly and the transformation process involving the stimulated emission of phonons and the formation of martensite is studied using a three-dimensional wave equation, Van der Pol's equation and Duffing's equation. The results are used to explain the main features of the martensitic transformation: the 'military' nature of the martensitic transformation (cooperative atomic movements), habit plane, mode softening, transformation plasticity, the reverse transformation on heating, etc. The emission ratio of coherent phonons in the quench process is given and is shown to be proportional to the cooling rate. The analogy between martensitic transformation and laser threshold is stressed. The analogy with the Landau theory of phase transformations and the difference between it and the present model are pointed out.