Formation of e/a-constant phases in the Ti–Zr–Ni–Cu system

Based on an optimized quasicrystal-forming composition Ti40Zr40Ni20 (numbers indicate at.%), e/a (valence electron per atom)-constant plane with e/a value of 1.2 and Ra (average atomic size)-constant plane with Ra value of 0.1474 nm are constructed in the Ti–Zr–Ni–Cu system, and a series of Ti–Zr–Ni–Cu alloys are designed along the intersecting line of the two planes. The experimental results showed that the single-phase quasicrystals can be obtained by the casting method at the compositions of Ti40Zr40Ni20 and Ti33Zr44Ni18Cu5, and a bulk glassy alloy is formed at the composition of Ti12Zr55Ni13Cu20. In the Ti3Zr60Ni12Cu25 and Zr60Ni10Cu30 alloys, the tI-(Zr,Ti)2(Cu,Ni) tetragonal phase becomes the dominant phase. Theoretical analysis revealed that the above three types of phases belong to a group of e/a-constant electronic compounds, and there exists close relationship in their local atomic structure, which is supported by the crystallization event of the Ti12Zr55Ni13Cu20 bulk metallic glass.