Again regarding the Al−Pd phase diagram

The Al−Pd phase diagram was experimentally reinvestigated in the region around the equiatomic composition. The high-temperature β-phase (CsCl-type structure) forming around AlPd transforms by cooling to a rhombohedral β′-phase, which only being metastable, strongly resists transformation to the stable low-temperature μ-phase (FeSi-type structure). The composition of the β-phase ranges between Al57.5Pd42.5 (at 949 °C) and Al45Pd55 (at 1315 °C). The highest existence temperature of the μ-phase is 745 °C at ∼Al52Pd48. The reaction β ↔ μ + δ occurs at 735 °C and Al53Pd47 composition; the reaction β ↔ μ + ν occurs (provisionally) at somewhat below 630 °C and ∼Al48Pd52 composition. No eutectoid decomposition of the ν-phase was observed down to 400 °C. A compositional continuity of the high-temperature complex ε6 and ε28 phases is argued.

► The constitution around AlPd is reinvestigated.
► The β′-phase forming by cooling from the high-temperature β-phase is metastable.
► Only the μ-phase corresponds to equilibrium below 745 °C.
► The β′-phase strongly resists its transformation to the μ-phase.