Evolution of phases in Al–Pd–Co alloys

The Al68Pd14.6Co17.4 and Al69.8Pd13.8Co16.4 alloys were investigated after continuous cooling and/or annealing at 700 °C for 2000 h. In the investigation light microscopy, scanning electron microscopy including energy dispersive X-ray spectroscopy, X-ray diffraction, electron backscatter diffraction, and differential thermal analysis were used. In the as-annealed near-equilibrium conditions of the Al68Pd14.6Co17.4 and Al69.8Pd13.8Co16.4 alloys U + β + Al5Co2 and U + Al5Co2 were identified, respectively. The U-phase in a majority of investigated samples was found to consist of 2–3 mutations differing from each other in metal composition, but exhibiting the same crystal structure. The mutations showed compositional features of their parent phases (liquid, V, and β). ▪ ► Al–Pd–Co system was studied in non- and near-equilibrium states. ► Combinations of U, β and Al5Co2 phases were identified in the studied alloys. ► U-phase was observed as dominant phase. ► Non-equilibrium U-phase was found to consist of 2–3 compositional mutations. ► Mutations of U-phase exhibited compositional features of their parent phases.