STRAIN-INDUCED STRUCTURAL-CHANGES AND CHEMICAL-REACTIONS - I - THERMOMECHANICAL AND KINETIC-MODELS

Strain-induced chemical reactions were observed recently (Nesterenko e t al., Appl. Phys. Lett., 1994, 65(24), 3069; Metall. Met. Trans. A, 1 995, 26, 2511) in experiments in the shear band in both Ti-Si and Nb-S i mixtures. Reactions can start in the solid slate or after melting of at least one component. One of the aims is to find theoretically, whe ther there are possible macroscopic mechanisms of mechanical intensifi cation of the above and other chemical reactions due to plastic shear in the solid stale. Continuum thermodynamical theory of structural cha nges with an athermal kinetics, which includes martensitic phase trans formations, plastic strain-induced chemical reactions and polymorphic transformations, is developed at finite strains. The theory includes k inematics, criterion of structural change and extremum principle for d etermination of all unknown variable parameters for the case with negl ected elastic strains. Thermodynamically consistent kinetic theory of thermally activated structural changes is suggested. The concept of th e effective temperature is introduced which takes into account that te mperature can vary significantly (on 1000 K) during the chemical react ions under consideration. The theory will be applied in Part II of the paper for the description of chemical reactions in the shear band. (C ) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All r ights reserved.