DIFFUSION OF COBALT, CHROMIUM, AND TITANIUM IN NI3AL

Diffusion studies of cobalt, chromium, and titanium in Ni3Al (gamma) at temperatures between 1298 and 1573 K have been performed using diffusion couples of (Ni-24.2 at. pct Al/Ni-24.4 at. pct Al-2.91 at. pct Co), (Ni-24.2 at. pct Al/Ni-23.1 at. pct Al-2.84 at. pct Cr), and (Ni-24.2 at. pct Al/Ni-20.9 at. pct Al-3.17 at. pct Ti). The diffusion profiles were measured by an electron probe microanalyzer, and the diffusion coefficients of cobalt, chromium, and titanium in gamma' containing 24.2 at. pct Al were determined from those diffusion profiles by Hall's method. The temperature dependencies of their diffusion coefficients (m2/s) are as follows: D(Co) = (4.2 +/- 1.2) x 10(-3) exp {-325 +/- 4 (kJ/mol)/RT} D(Cr) = (1.1 +/- 0.3) x 10(-1) exp {-366 +/- 3 (kJ/mol)/RT} and D(Ti) = (5.6 +/- 3. 1) x 10(1) exp {-468 +/- 6 (kJ/mol)/RT} The values of activation energy increase in this order: cobalt, chromium, and titanium. These activation energies are closely related to the substitution behavior of cobalt, chromium, and titanium atoms in the L1(2) lattice sites of gamma'; the cobalt atoms occupying the face-centered sites in the L1(2) Structure diffuse with the normal activation energy, whereas the titanium atoms occupying the cubic comer sites diffuse with a larger activation energy that includes the energy due to local disordering caused by the atomic jumps. The chromium atoms which can occupy both sites diffuse with an activation energy similar to that of cobalt atoms.