Icosahedral phase stabilities in Al-Cu-Ru alloys

By examining a wide region of the Al-Cu-Ru phase diagram, a thorough analysis of the compositional and thermal stability of the icosahedral phase has been completed. The primary solidification product of rapid solidification was a topologically and chemically disordered icosahedral phase with an extensive compositional region. Crystallization through exothermic events of the as-solidified materials produced crystalline phases, without the formation of the face-centered-icosahedral (FCI) phase. However, the FCI phase does form at higher temperatures through an endothermic reaction, indicating that it is a stable phase of the system, but only at elevated temperatures. Of the alloys studied, the FCI phase field was found to encompass ${\mathrm{Al}}_{65}$ ${\mathrm{Cu}}_{23}$ ${\mathrm{Ru}}_{12}$, ${\mathrm{Al}}_{65}$ ${\mathrm{Cu}}_{20}$ ${\mathrm{Ru}}_{15}$, ${\mathrm{Al}}_{70}$ ${\mathrm{Cu}}_{20}$ ${\mathrm{Ru}}_{10}$, and ${\mathrm{Al}}_{70}$ ${\mathrm{Cu}}_{15}$ ${\mathrm{Ru}}_{15}$. The transformation to the FCI phase involves an intermediate approximant phase that is very similar to the FCI structure. Also, a cubic approximant containing atomic arrangements with local icosahedral symmetry similar to α-Al Mn Si was determined to exist near the FCI phase field.