Reaction diffusion and Kirkendall-effect in the nickel-aluminum system

Chem. diffusion coeffs. and heats of activation for diffusion in the Ni2Al (g), NiAl (d), and Ni3Al (e) intermetallic phases and the solid soln. of Al in Ni (z phase), were calcd. from layer growth expts. No finite diffusion coeff. for the NiAl3 (b) intermetallic phase could be calcd. The values of the diffusion coeffs. are dependent both on the method of calcn. and the type of diffusion couple. The heat of activation for diffusion in the g phase was 47 kcal./mole in the range 428-610 Deg. Heats of activation of 41, 12, and 48 kcal./mole were found for diffusion in the d, e, and z phases, resp., in the range 655-1000 Deg. Expts. with markers in the diffusion zone demonstrate a very pronounced Kirkendall effect. It appears that only Al atoms take an active part in the diffusion process during the formation of the b and g phases at .apprx.600 Deg. During the formation of the d, e, and z phases at higher temps. only Ni atoms are moving. It is suggested that the great stability of the intermetallic compds. in the Ni-Al system governs the Kirkendall effect. 20 references. [on SciFinder (R)]