On transient layers as new phase domains in composite materials

Abstract

A model describing the development of transient layers as new phase domains in compositematerials is constructed under the assumption that the transient layers around (nano)particles are layers of the matrix material changed by the phase transformation and increase the effective volume of inclusions which become compound and consist of the nucleus (original particle) and the shell (transient layer of the new phase). As a result, the inclusion volume fraction increases, which, in turn, increases the particle influence efficiency. An example of spherical particles is used to consider the new phase development around an isolated particle and then, in the effective field approximation, around interacting particles in the composite material. The dependence of the compound inclusion radius on the external (averaged) strain is obtained for isotropic phases. Stability of the interphase boundaries depending on the parameters of the original inclusion material and the matrix phase materials is studied. The energy variations and the stress redistribution owing to the development of the new phase domains are considered in detail. It is shown that, in the case of an isolated inclusion, the development of a new phase may lead to a local energy decrease near the inclusions and, as a consequence, to a decrease in the stress concentration. At the same time, the formation of transient layers due to the phase transformation can result in an increase in the bulk modulus of elasticity as the effective shear modulus decreases.