Scripta METALLURGICA Vol. 6, pp. 203-208, 1972 Pergamon Press, Inc. Printed in the United States TEMPERATURE COEFFICIENT OF TWIN-BOUNDARY ENERGY: THE DETERMINATION OF STACKING-FAULT ENERGY FROM THE COHERENT TWIN-BOUNDARY ENERGY IN PURE F.C.C. METALS L.E. Murr Department of Materials Science University of Southern California Los Angeles, Calilornia 90007 (Received January I0, 1972) The measurement of the coherent twin boundary energy for pure f. c. c metals has been of considerable interest for more than two decades as a possible means for determining the stacking-fault energy through the simple relationship YSF -=" 2Ytb; where ~F is the stacking- fault energy, and Ytb is the coherent twin boundary energy. This relationship obtains from the simple geometrical consideration that intrinsic and extrinsic stacking faults in f. c. c. metals are ideally regarded as twin boundaries separated by one or two (Iii) planes respectively. While there have been numerous attempts to calculate YSF from values of ~b measured as ratios of Ytb/Vgb or ~b/FS at high temperature (where the grain boundary energy, ~b' and the surface free energy, F S, have been determined as an absolute (average) value by the method of zero creep), none have produced values of 7SF in agreement with the more acceptable (and direct) room temperature measurements of YSF from stacking-fault nodes using the electron microscope. The reason for this disagreement, as pointed out by several investi gators (i-3), has been the implicit or deliberate assumption that the temperature coefficients of twin or stacking-fault energies are negligible. The concept of temperature coefficient is implicit in the Gibbs fundamental equation (4) for an interface considered as a homogeneous phase (5) -d y = s dT ÷ where 7 is the interracial free energy, S is the interracial entropy, I'. is the number of i moles of the ith component per unit area of the interface, ~i is the associated chemical potential, and T is the temperature. }'or a single-component system (a pure metal), Eq. (i) becomes simply / % - d(-r~l = s (z) V 203