Relative Interfacial Free Energy Measurements in Cu and Cu-Al Alloys

Measurements of gamma tb/gamma gb for Cu and Cu-A1 alloys utilizing transmission electron microscopy and selected-area electron diffraction techniques, and measurements of gamma SF for Cn-Al alloys from observations of extended dislocation nodes have shown that both gamma tb/gamma gb and gamma SF decrease with increasing atomic percent Al. Values of gamma tb = 26 erg/cm(2) and gamma gb = 730 erg/cm(2) at 700 degrees C were estimated by correcting previous experimental values of gamma gb for Cu. By assuming the value of gamma gb in Cu to be reduced by approximately 10% upon t'he addition of 16 at yo Al, the minimum value of the coherent twin boundary free energy over the range of alloying studied was estimated to be gamma tb = 12 erg/cm(2). Mean values of gamma tb/gamma gb - 0.031, 0.029, and 0.018 were measured for the Cu-5, 11, and 16 at yo A1 samples respectively corresponding to an equilibrium temperature of 700 degrees C. By plotting values of gamma tb/gamma gb as a function of misorientation, theta, between < 110 > directions for rotations about [100] for Cu and [110] for the Cu-Al alloys, a definite variation of grain boundary free energy with misorientation was established. The spread of histograms of gamma tb/gamma gb was also shown to be related to this variation in gamma gb with theta. Energy cusps were observed in the grain boundary free energy curves.