STRAIN-INDUCED STRUCTURAL-CHANGES AND CHEMICAL-REACTIONS - II - MODELING OF REACTIONS IN SHEAR-BAND

The problem on strain-induced chemical reaction (SICR) and structural changes (SCs) in a thin layer inside the shear band is formulated and solved for large strains. It is analytically demonstrated that intense plastic deformation can accelerate chemical reactions. The phenomenon of reaction-induced plasticity (RIP), similar to transformation-induc ed plasticity at phase transitions is derived and modelled. A criterio n for athermal SICR is derived and distinctive points of the approach proposed at zero shear stresses and classical chemical thermodynamics are analysed. Two mechanisms are proposed for the experimentally obser ved positive effect of shear stresses on SC from the low temperature p hase to the high temperature phase. The first one is related to the ne cessity of fulfilment of the yield condition for the transforming mate rial. The second mechanism is connected with the additional heating du e to RIP. A kinetic criterion of chemical reaction is formulated. As a n example, the SICR in Ti-Si and Nb-Si mixtures is considered. It is s hown that the main reason for acceleration of reaction kinetics due to shear stress or strain is related to the increase of effective temper ature due to RIP. The increase of driving force due to shear stresses does not affect the kinetics. (C) 1998 Acta Metallurgica Inc. Publishe d by Elsevier Science Ltd. All rights reserved.