Constitution of the high-Al region of Al-Cu-Rh

Phase equilibria between 540 and 1010 °C were studied in Al-Cu-Rh alloys containing more than 50 at.% Al. Congruent equiatomic AlRh dissolves more than 40 at.% Cu and extends up to 58 at.% Al at the high-Cu part of its compositional range. High-temperature cubic C-Al5Rh2 (C-phase) dissolves up to 13 at.% Cu, “Al3Rh” (ɛ6-phase) up to 15 at.% Cu and Al9Rh2 up to 1.5 at.% Cu. The solubility of the third element in other binary Al-Rh and Al-Cu phases is below 0.5 at.%. Close to the high-Cu limit of the C-phase region the fcc C2-phase structurally related to the C-phase is formed. Stable decagonal phase (D1-phase) is formed below 1005 °C in a compositional range extending from Al65Cu16Rh19 to Al62Cu23Rh15, which shifts to higher Cu concentrations with decreasing temperature. An additional ternary phase forming around the Al70Cu20Rh10 composition below 660 °C was revealed. Partial 1010, 990, 900, 800, 700, 600 and 540 °C isothermal sections were determined.