Place: DPG Spring Meeting, Dresden, Germany
Ni-base superalloys are widely used in high-temperature applications, e.g. in turbine blades for jet engines of aeroplanes. In these applications, the materials have to perform at high temperature and high stress. Ni-base superalloys have a complex composition where one of the key ingredients is Re, which significantly improves the mechanical behaviour. Using density functional theory (DFT) calculations, we investigate the Re-Re interaction in Ni with a particular focus on the role of magnetism. The nearest neighbour Re-Re interaction in the nonmagnetic and in the ferromagnetic configuration exhibit a qualitatively different behaviour from strongly repulsive to weakly attractive. We show that this is mainly due to a decrease of the Ni magnetic moment in the vicinity of Re and discuss possible consquences for the clustering of Re in Ni-based superalloys. In a next step we investigate the mobility of Re in Ni in concentrated Ni-Re alloys. As a basis for our dynamical simulations, we use a cluster expansion (CE) to evaluate the energies of the binary Ni-Re and the ternary Ni-Re-vacancy system. DFT calculations are used to determine the effective cluster interactions (ECI) for the CE. We will also report on our progress of a CE for the diffusion barriers, which - when converged - enables us to predict diffusion in concentrated Ni-Re alloys from first-principles calculations.