Interdiffusion in ternary Ni3Al/Ni3Al-X diffusion couples with X=Cr, Fe, Nb and Ti

The γ′ single phase interdiffusion in selected pseudo-binary sections of the Ni3Al-X (X=Cr, Fe, Nb and Ti) ternary alloys was studied in temperature interval 1173–1533 K in order to assess the influence of the site-preference of components upon their diffusion rate. It was observed that (a) Higher fraction of Cr or Fe on Al sublattice leads to lower values of D̃XX(Ni). (b) Both Ti and Nb, preferring strongly the Al sublattice, show significantly lower interdiffusion coefficients than Fe and Cr. (c) The equation D̃XX(Ni)=D̃AlAl(Ni) holds for Ti and Nb, whereas the relation D̃XX(Ni)>D̃AlAl(Ni) is valid for Cr and Fe. (d) Activation enthalpy of Qii(j) shows a systematic decrease with increasing valence electron number of the alloying element i. (e) Nb shows a transient behavior Q—it has low values of diffusion coefficient compared to its site occupation but also a low activation energy.