The method of zero creep of small-diameter 304 stainless steel wires coupled with scanning and transmission electron (shadowgraphic) microscopy of grain boundary-surface intersection grooves was used to measure average values for the surface free energy and the grain boundary free energy at 1060, 1160, 1260 and 1360C, from which the temperature coefficients of the specific interfacial free energies were measured to be -1.760 and -0.890mJ/m2C. respectively. Mean values of the coherent twin boundary free energy/grain boundary free energy ratios were determined for low-torque twin-grain boundary intersections in thin foils of 304 stainless steel, using transmission and diffraction electron microscopy. They were 0.016, 0.017, 0.024 and 0.024 for 910, 985, 1060 and 1180C, respectively. From these data, the temperature coefficient of the twin boundary free energy was determined to be 0.007mJ/m2C. By assuming the temperature coefficients measured at elevated temperatures to be linearly extendable to room temperature, the 25C-values of the surface and grain-boundary energies were expected to be 3975 and 1670mJ/m2, respectively. The room-temperature value of the stacking-fault free energy was determined to be 20mJ/m2. Differences in sign of the temperature coefficients of surface and grain boundary free energies, compared with the temperature coefficient of the twin boundary free energy, suggested the existence of phenomenologically different segregation thermodynamics at these interfaces.

Measurement of Interfacial Free Energies and Associated Temperature Coefficients in 304 Stainless Steel. L.E.Murr, G.I.Wong, R.J.Horylev: Acta Metallurgica, 1973, 21[5], 595-604