Sublimation, chemical decomposition, and melting inside an elastoplastic material: General continuum thermodynamic and kinetic theory

General thermodynamic and kinetic approaches for sublimation inside an elastoplastic material are developed for large strains. Various conceptual problems related to the effect of irreversible plastic deformation and dissipation, path-dependence of the appearance of a critical nucleus, and the presence of large strains are considered. Two transformation paths are studied: nucleation via homogeneous transformation in the nucleus of fixed mass and nucleation via continuous interface propagation. For both paths, the expressions for the thermodynamic driving forces and activation energies are derived. The activation energy is equal to the negative driving force for the appearance of a nucleus maximized with respect to nucleus mass and minimized over the nucleus shape, transformation path, and position. This definition corresponds to the principle of the minimum of transformation time and reduces to the traditional one in the limit of elastic materials. An Arrhenius-type kinetic equation for nucleation time and kinetic nucleation criterion are formulated. Algorithms for the determination of the critical nucleus are suggested. After appearance of the nucleus via homogeneous transformation, the possibility of its growth should be checked. Growth may occur by further sublimation or by mechanical expansion without phase transformation due to mechanical instability. Because the driving force for forward and reverse transformations maybe different, several scenarios are possible. The nucleus can grow, disappear, or be arrested; in the last case, it represents a stable rather than a critical nucleus. It is demonstrated that with small modifications, our approach to sublimation can be applied to chemical decomposition and melting inside an elastoplastic material. In the accompanying paper (Levitas and Altukhova, 2012) we will apply the developed theory to nucleation of a spherical gas bubble inside an elastoplastic material.

► General thermodynamic and kinetic approach for sublimation in elastoplastic material.
► Concept of a critical nucleus inside elastoplastic material and its path-dependence.
► Growth of a critical nucleus via interface propagation and mechanical instability.
► Chemical decomposition and melting inside elastoplastic materials.
► Arrhenius-type kinetic equation and principle of the minimum of transformation time.