Stable quasicrystalline phase in Al-Cu-Fe-Cr coating materials

Transmission electron microscopy (TEM) studies have been carried out on magnetron-sputtered coatings in the Al-rich region of the Al-Cu-Fe-Cr quasicrystalline phase field, focusing on the composition that exhibited the best tribological performance among a group of sputtered coatings. The size of the particles in the as-deposited coating is around 10 nm. The TEM experiments on annealed coatings (450 °C for 6 hours+400 °C for 7 hours) revealed that the material is composed of a decagonal quasicrystalline phase with a periodicity of 1.24 nm along the unique axis and a hexagonal crystalline phase, with a=2.48 nm and c=1.24 nm. These results show that a thermodynamically stable quasicrystalline phase exists in the Al-Cu-Fe-Cr alloy system, in addition to previously reported microcrystalline structures and orthorhombic and monoclinic approximants. The hexagonal phase is a crystalline approximant of the decagonal phase, structurally related to hexagonal crystalline phases previously reported in Al-Mn and Al-Cr-Ni quasicrystalline alloys.