Abstract
Metastable Zr100x Alx alloys have been formed by ball milling of elemental Zr and Al powders: supersaturated hcp solid solution for x≤15, and an amorphous phase for x≥17.5. Enthalpy-composition curves for both phases were determined by measurements of the enthalpy of transformation to equilibrium. A cusp indicating the crossover of these two curves is observed near the critical composition for amorphization. Our results indicate that phase formation by ball milling in Zr-Al is determined by polymorphous constraints and not by nucleation and growth under metastable two-phase equilibrium.