Understanding the glass-forming ability of Cu50Zr50 alloys in terms of a metastable eutectic

Interest in finding binary alloys that can form bulk metallic glasses has stimulated recent work on the Cu-Zr system, which is known to show glass formation over a wide composition range. This work focuses on copper mold casting of Cu50Zr50 (at.%), and it is shown that fully amorphous rods up to 2-mm diameter can be obtained. The primary intermetallic phase competing with glass formation on cooling is identified, and the glass-forming ability is interpreted in terms of a metastable eutectic involving this phase. Minor additions of aluminum increase the glass-forming ability: with addition of 4 at.% Al to Cu5oZr50, rods of at least 5-mm diameter can be cast fully amorphous. The improvement of glass-forming ability is related to suppression of the primary intermetallic phase.