Alloy aging as a multiscale effect within the nanocomposite theory

Within the theory of finely dispersed nanocomposites, the dependence of the effective Young's modulus on the absolute size of the reinforcing particles is obtained. Two cases of controlling/changing the effective Young's modulus at a constant relative volume fraction of reinforcing particles are considered. The first is the disintegration of reinforcing particles into smaller ones, followed by diffusion throughout the volume of the matrix. In this case, the effective modulus of the nanocomposite increases. The second one is the agglomeration of reinforcing particles into larger ones. In this case, the effective modulus of the nanocomposite decreases. These patterns seem to be universal and independent of heat treatment technology. It can be assumed that the agglomeration or decomposition of the reinforcing particles depends on the choice of a heat treatment technology for a nanocomposite. It is important to emphasize that the selected heat treatment technology is to be such that during the heat treatment no phase transitions occur either in the material of the reinforcing particles or in the matrix material. It is necessary to eliminate the appearance of phase transitions, since the new phase represents a field of defects, in particular, the field of substitutional dislocations. For such processes, the gradient theory of a defect-free medium is no longer valid. It is necessary to build models of defective environments that are more complex. Therefore, this article does not consider the criteria for choosing a heat treatment technology. The question remains open that, along with the gradient generalization of the theory of composites, a nonlinear generalization is possible. Indeed, unlike ceramics, which retain physical linearity almost until destruction, metal composites exhibit plasticity over a large range of deformations. However, generalization to physical nonlinearity, and even more so to plasticity, is complicated by the fact that there is still no generally accepted theory for constructing a stress-strain curve even for homogeneous materials.