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

Abstract

Structural stability with respect to heat treatments of the Al-Co-Cu-Ni decagonal phase has been explored. Deca-gonal phases are stabilized in Al-Co-Cu-Ni alloys with Al(,;CoicCu,)) and Ah5)Coj, Nii5 as ternary end members. Characteristic features of this alloy series have been reported earlier. Both in the as-cast and rapidly soli-dified 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 A16.h5- Co1. Cu5, i:NijO and Al67Co15Cu5Nii() 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.