Intermetallics in the Zr–Al diffusion zone

Solid-state diffusion reaction between Zr and Al was studied in the temperature range 838–898 K employing bulk diffusion couples. The intermetallic phase ZrAl3 forms in the diffusion zone in all the diffusion couples in planar morphology. A second layer of Zr2Al3 forms in addition, at and above 873 K in the diffusion zone. The formation of ZrAl3 as the first phase was rationalised on the basis of the Modified Effective Heat of Formation (MEHF) model. The driving forces for formation of Zr2Al3 and ZrAl2 at the Zr/ZrAl3 interface were evaluated. The appearance of Zr2Al3 in preference to ZrAl2 at higher temperatures is attributed to the higher driving force for its formation at the Zr/ZrAl3 interface. The temperature dependence of growth of ZrAl3 phase layer was determined. The activation energy (Qk) for growth of ZrAl3 is 188.2±2.5 kJ/mol and the pre-exponential factor (k0) is 2.9−0.35+0.55×104 ms12.