An Absolute Determination of the Extrinsic and Intrinsic Stacking Fault Energies in AgIn Alloys

Abstract

AbstractObservations have been made of extrinsic‐intrinsic node pairs, and of a hitherto unreported fault pair. It is shown that a simple estimate of the ratio of extrinsic to intrinsic stacking fault energy (γe/γi) cannot be made from the inscribed radii of node pairs, and that earlier qualitative results that γe/γi > 2, or more, are invalid. The simple geometry of the new fault pair facilitates a straight forward absolute determination of both γe and γi. Contrary to published results, γe and γi have been found to be approximately equal. For the present alloys, γe/γi = 1.09 ± 0.1 (for the electron —atom ratio e/a = 1.15) and γe/γi = 1.03 ± 0.1 (for e/a = 1.23). Good absolute agreement has been obtained between γi determined from the fault pairs, and from the observation of extended three‐fold nodes. It is concluded that extrinsic faults are rarely observed because of a high impedance to their formation arising from the co‐operative glide which is necessary, but that, once formed, the extrinsic fault energy is closely the same as the intrinsic.