Self- and impurity diffusion of Ni, Ga, Ge, Ti, Nb and Bin the L1(2)-type intermetallic compound Ni3Al

Self- and impurity diffusion of Ni, Ga, Ge, Ti Nb and B was investigated in Ni3Al single and polycrystals. Ni self-diffusion was investigated applying two techniques of profile detection. At high temperatures profiles were obtained by an improved serial sectioning technique, while at low temperatures and small diffusion coefficients, respectively, concentration profiles were determined by secondary ion mass spectrometry (SIMS). It is concluded from the present data that Ni diffusion occurs via nearest-neighbour jumps of only thermal vacancies in the Ni-sublattice. Because of the lack of a suitable Al-tracer, Al-diffusion in the compound was simulated by investigating the diffusion behaviour of Ti, Nb, Ge and the homologous element Ga, which are preferentially located on Al sites. The difference in the observed enthalpies Q(Ga) and Q(Ni) agrees well with the predicted energy of antisite defect formation of Al in the Ni-sublattice (44.4 kJ mol(-1)). Therefore, it is most likely that diffusion of Ga occurs via nearest-neighbour jumps using Ni-vacancies in the Ni-sublattice. A lower diffusivity of Ti and Nh in comparison to Ga and Ge combined with a slightly enhanced activation enthalpy is observed. The smaller activation enthalpy and the 3 to 4 orders of magnitude higher diffusivity of the B atoms indicate that B diffuses interstitially in the L1(2)-type Ni3Al lattice. The still relative high value of Q(B) of such an interstitial mechanism is attributed to the strong asymmetrical occupancy of the two energetically different types of octahedral interstitial sites in Ni3Al by the B atoms and the diffusion path resulting from the corresponding structural and energetical conditions.