On the estimation of SRO effects on surface segregation

The free-energy concentration expansion method (FCEM) is introduced and app lied to the elucidation of short-range order (SRO) effects on surface segre gation in alloys. This statistical-mechanical analytical approach, based on the Ising model Hamiltonian energetics, is verified by Monte Carlo (MC) si mulations. In particular, calculations performed for the (100) surface of f ee solid solution show that the FCEM agrees with MC results much better tha n the Bragg-Williams (BW) theory, including the prediction of an increase i n equilibrium segregation level with temperature, associated with SRO/segre gation competition. FCEM is quite accurate and simple to apply, demanding m uch less computational effort compared to MC simulations or the cluster var iation method. It can replace the corresponding BW formulae in theoretical evaluation of various surfaces as well as bulk phenomena, allowing systemat ic studies of SRO effects in alloys.