Simulation of the Tracer Diffusion, Bulk Ordering, and Surface Reordering in F.C.C. Structures by Kinetic Mean-Field Method

• Main Author: V. M. Bezpalchuk, R. Kozubski, A. M. Gusak
• Format: Article
• Language: English
• Published: G. V. Kurdyumov Institute for Metal Physics of the N.A.S. of Ukraine 2017-09-01
• Series: Успехи физики металлов
• Online Access: https://doi.org/10.15407/ufm.18.03.205

Tracer diffusion and ‘chemical’ (atomic) ordering processes in two face-centred cubic (f.c.c.) binary systems mimicking Ni3Al and FePt were simulated by means of the kinetic mean-field (KMF) method originally proposed by G. Martin in 1990. The systems simulated within the present work were modelled with fixed pair-interaction parameters and saddle-point energies adopted earlier via the comparison of Monte Carlo method modelling and experimental data. In a simulation of tracer migration as well as ordering, the focus was attracted to comparison of activation energies rather than pre-exponential factors of kinetic coefficients. Generally, the mean-field models cannot properly take into account correlation effect that could be important for the tracer diffusion especially for the B2 structures. However, at least for the f.c.c. structures, application of KMF to diffusion and ordering seems demonstrating very reasonable results qualitatively similar to those obtained in kinetic Monte Carlo (KMC) method and realistic experiments. Modelling of Ni- and Al-tracer diffusion in Ni3Al system shows higher diffusivity of Ni atoms as compared with Al ones that is attributed to easier intrasublattice diffusion channel for the Ni atoms in the L12-Ni3Al superstructure. Also, the obtained activation energy for the tracer Al atoms is higher, and its value is closer to activation energy of ordering kinetics. Computer experiments for the ordering kinetics showed that, in contrast to exchange mechanism, L12-type ordering kinetics is described via two relaxation times in case of the vacancy diffusion mechanism. Modelling of the discontinuous process of the surface-induced re-orientation of the monatomic Fe and Pt planes in thin FePt film was, in turn, a good test for the stochastic variant of the KMF (SKMF) method. The fact that implementation of the stochastic noise was needed to reproduce the process of a surface nucleation by KMF indicates the correctness of the method.