Materials Science Forum, Vol.386-3, 235-244, 2002
Chemomechanical effects accompanying mechanochemical reactions and creep
Mechanochemical phenomena are often interpreted through the mechanochemical effect (MCE) manifesting itself by a change in the chemical reaction rate assisted by mechanical stresses in solids. However, as it was shown using non-equilibrium thermodynamics, there exists inevitably a conjugated cross-effect that I have called chemomechanical effect (CME). It manifests itself by a change in the mechanical state of a solid and plasticity increase due to the influence of chemical (electrochemical) reaction on its surface causing an additional dislocation flux. Earlier the existence of CME was directly confirmed by hardness measurements under the conditions of anodic polarization or crystalline material etching. Now we analyze CME relevant to the problems of creep and fracture in solids. For a quantitative description of MCE and CME and experimental verification, one should proceed from basic kinetic equations for the reaction rate and creep rate, respectively. To explain the mechanism of CME it is interpreted as the phenomenon caused by heterogeneous nucleation and action of new sources of dislocations resulting from heterogeneous surface dissolution. The role of surface conditions in plastization of a solid is discussed, and differences of CME from other surface effects (e. g., Rehbinder effect) are shown. The hew kind of stress corrosion called corrosion creep is demonstrated for Mg and Mg alloys as a consequence of CME and MCE autocatalitic interaction. The next problem will be to find CME in amorphous materials (e.g., metal glasses) where MCE has been already found experimentally.
Keywords:creep;dislocations;electrochemical kinetics;mechanochemical reactions;nonequilibrium thermodynamics