Interdiffusion and thermotransport in engineering materials

In this research in Part A (Macroscopic Description), (1) the Hall method (HM) (specifically designed for determining the interdiffusion coefficient at the low and high composition limits of the corresponding interdiffusion composition profile) is further developed in order to be applied to the whole composition profile resulting in the Extended Hall method (EHM); (2) A comparative study of the HM, EHM, Boltzmann-Matano (BM) and Sauer and Freise (SF) methods is performed using composition profiles generated by computer simulation. The results clearly indicate that the HM/EHM technique is only applicable when the interdiffusion coefficient is constant (i.e. independent of composition) or almost constant at the low composition regions. In all other cases, the BM and SF methods give the best agreement with the input interdiffusion function even at the ends of the composition profiles. In Part B ((Microscopic Description) of this thesis, the thermodynamic and thermophysical properties of the liquid Ni-Al alloys are studied over a wide temperature and concentration range by using molecular dynamics (MD) simulations. The calculations are performed by using equilibrium molecular dynamics simulation in conjunction with the Green-Kubo formalism and one of the most reliable embedded-atom method potentials for this system developed by Purja and Mishin. For an equi-atomic liquid Ni-Al alloy, the calculations are also executed on another potential. The results permit the description of the temperature and concentration dependence of the thermodynamic factor for interdiffusion. Furthermore, the simulations permit analysis of the heat of transport in thermotransport. It is possible to estimate the contributions of Onsager off-diagonal terms for the temperature and concentration range under consideration. Accordingly, in the presence of a temperature gradient, our simulation results for all the considered models of liquid Ni-Al alloys predict consistently Ni and Al to migrate to the cold and hot ends, respectively. Meanwhile, the highest value, about 1.1 ± 0.1 eV, of the reduced heat of transport is observed for Ni₂Al₂ alloy model and it slightly decreases towards Al-rich and Ni rich compositions. The results agree well with previous published experimental and simulation data where available.