Effect of the addition of Ag on the strengthening of Al3Li phase in Al-Li single crystals

Abstract

The variation of the critical resolved shear stress as a function of aging condition has been measured in ternary Al- similar to (1.9-2.0) wt% Li- similar to 0.4 wt% Ag single crystals and has been analyzed using the same version of order-hardening theory as in our previous work in binary single crystals. The result showed that the antiphase boundary energy of the Al3Li lattice on {111} definitively increases from about 0.118 J/m(2) in binary crystals to 0.125 +/- 0.012 J/m(2) in ternary crystals, in good agreement with the analysis of the transition behavior from shearing to looping and of the dislocation pair spacings. A strong segregation tendency of Ag into the Al3Li lattice is believed to be responsible for this increment. Our previous result of gamma(apb) (0.118 +/- 0.006 J/m(2)) in binary crystals is, although unlikely from the recent suggestion of Nembach, the best value one can obtain from the recent knowledge of order-hardening theory. This is slightly larger than that (about 0.100 J/m(2)) obtained from the analysis of the transition from shearing to looping and somewhat larger than the result (about 0.085 J/m(2)) of the first-principles calculation. Three factors are discussed as principal causes of a possibility of an overestimation of gamma(apb) on applying order-hardening theory. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.