Structural stability of Al–Co–Cu–Ni decagonal phase

Structural stability with respect to heat treatments of the Al–Co–Cu–Ni decagonal phase has been explored. Decagonal phases are stabilized in Al–Co–Cu–Ni alloys with Al ₆₅Co ₁₅Cu ₂₀ and Al ₇₀Co ₁₅Ni ₁₅ as ternary end members. Characteristic features of this alloy series have been reported earlier. Both in the as-cast and rapidly solidified condition they form decagonal phases. From a knowledge of the differential thermal analysis plots of the alloys, and on the basis of earlier studies, two compositions Al _68.85Co ₁₅Cu _6.15Ni ₁₀ and Al ₆₇Co ₁₅Cu ₈Ni ₁₀ were selected. Samples were annealed at 900 °C for 435 h for the as-cast alloy of the former composition and at 450 °C for 65 h for the rapidly solidified alloy of the latter one. Only for the latter composition, were samples ion milled prior to TEM investigations. In both samples, we observed a lowering of symmetry in the 10-fold diffraction patterns with annealing.