The diffusion coefficients of Pt and Mo in Ni and Ni3Al(γ′) were determined (figure 24) by using Hall's method and diffusion couples. The temperature dependences were described by,

DPt(γ′)(m2/s) = 7.8 x 10-4exp[-323(kJ/mol)/RT]

DMo(γ′)(m2/s) = 2.3 x 102exp[-493(kJ/mol)/RT]

DPt(Ni)(m2/s) = 3.5 x 10-5exp[-280(kJ/mol)/RT

DMo(Ni)(m2/s) = 1.3 x 10-4exp[-283(kJ/mol)/RT]

From this study, the following mechanism of diffusion in Ni3Al was proposed: the diffusion of Pt atoms which substituted at Ni-sites (α) occurred mainly by random jumps from α- to α-sites through the vacancies on α-sites. The Mo atoms which substituted at Al-sites (β) jumped to α-sites with local disordering, and then diffused randomly through α-sites.

Diffusion of Platinum and Molybdenum in Ni and Ni3Al. Minamino, Y., Yoshida, H., Jung, S.B., Hirao, K., Yamane, T.: Defect and Diffusion Forum, 1997, 143-147, 257-62

Table 21

Arrhenius parameters for diffusion in Ni3Al

Figure 24

Diffusion of Mo and Pt in Ni3Al

White circles, Pt; black circles, Mo