Effects of finite temperature on the surface energy in Al alloys from first-principles calculations

Experimental measurement of surface energy is rather difficult at finite temperature. This work develops a first-principles method to estimate the effects of finite temperature on the surface energy of Al alloys. The surface energies of four planes, namely, (100), (110), (111) and (112) planes, have been calculated as a function of the finite temperature, as well as the interaction energies between the solute atoms and these surfaces. The uniform distribution (UFD) model is used to treat the distributions of solute atoms in investigating the microcrack nucleation mechanism. The results suggest that the four surface energies of pure Al decrease slightly with increasing the temperature. While Sn atom can drastically reduce the four surface energies of Al alloys at relatively high solute concentration, which obviously increases the probability of forming a new surface, inducing more microcracks in Al alloys. Interestingly, Cu atom can inhibit the microcrack nucleation of (100) and (111) surfaces by slightly increasing their surface energies. Microcracks in Al alloys prefer to nucleate along the (111) surface due to the lower surface energy. This work provides a valuable insight for further exploring the surface characteristics of Al alloys at finite temperature.