A combination of experimental techniques and molecular dynamics (MD) computer simulation is used to investigate the diffusion dynamics in Al80Ni20 melts. Experimentally, the self-diffusion coefficient of Ni is measured by the long-capillary (LC) method and by quasielastic neutron scattering. The LC method yields also the interdiffusion coefficient. Whereas the experiments were done in the normal liquid state, the simulations provided the determination of both self-diffusion and interdiffusion constants in the undercooled regime as well. The simulation results show good agreement with the experimental data. In the temperature range 3000 K≥ T ≥ 715 K, the interdiffusion coefficient is larger than the self-diffusion constants. Furthermore the simulation shows that this difference becomes larger in the undercooled regime. This result can be refered to a relatively strong temperature dependence of the thermodynamic factor Φ, which describes the thermodynamic driving force for interdiffusion. The simulations also indicate that the Darken equation is a good approximation, even in the undercooled regime. This implies that dynamic cross correlations play a minor role for the temperature range under consideration.

The diffusion of 63Ni and 114mIn in the intermetallic L12 phase Ni3Al is measured in the temperature range from 900 to 1200 °C and for compositions between 73.5 and 77 at% Ni in steps of 0.5 at%. The In isotope serves as a substitute for 26Al. The usual serial sectioning method is applied using a precision parallel grinder. There is only a weak concentration dependence of the diffusion coefficient at temperatures > 950 °C but it gets stronger with decreasing temperature. There is a minimum of the diffusion coefficient at 76 and not at 75 at% Ni as may be expected. The diffusion of 63Ni in Ni3Al and in pure Ni is comparable. The same is true for the diffusion of 114mIn in Ni3Al. Very likely the diffusion of 63Ni is by a normal vacancy mechanism and the diffusion of 114mIn by In antisite atoms in the Ni sublattice. The D 0*‐values are for In (and probably for Al as well) considerably higher than for Ni. This could be due to a higher entropy term. As a consequence of the considerably larger D 0*‐values of In an intersection of the two linear Arrhenius plots for Ni and Al is observed at about 950 °C for all concentrations except Ni76Al24. This fits well to interdiffusion investigations where at higher temperatures Al is found to be the faster component, and Ni at lower temperatures.

No abstract

No abstract

No abstract