Temperature Coefficient for Twin Boundary Free Energy in 304 Stainless Steel: An Electron Microscope Study

Abstract

It has been recently shown that, as generally assumed, the coherent twin boundary free energy and the intrinsic stacking fault free energy in fee pure metals are approximately related by a factor of 2 at constant temperature, i. e.,In the case of pure metals, the temperature coefficient assumes a simple Gibbs form for a general interface (stacking fault or twin boundary):where S is the interfacial entropy per unit area of interface. It is noted in Eq. (2) that the temperature coefficient for an idealized pure metal is always negative. Thus, in the absence of interfacial adsorption of vacancies or impurities [assumed in Eq. (2)], the stacking fault and twin boundary free energies will increase with increasing temperature, and will be related by Eq. (1).In the case of multicomponent (alloy) systems, the temperature coefficient becomes a complex function of component entropy contributions, surface adsorption and desorption, and their temperature dependence: