Effect of Cu substitution in Al–Co–Ni decagonal quasicrystals

A stable decagonal phase has been observed in both as-cast and rapidly solidified Al–Co–Ni and Al–Co–Cu alloys, which form in the composition range of 15–20 at.% Co and 10–15 at.% Ni or 15–20 at.% Cu. In the present investigation, copper was substituted for Co and Ni in Al70Co15Ni15. Compositions corresponding to Al70Co15−xCuxNi15 and Al70Co15CuxNi15−x were investigated. It is found that when the copper concentration reaches a value of 5 at.%, the disorder marker, i.e. the streaking along the 111,113 rows becomes predominant. For Al70Co15−xCuxNi15, when all of the Co is replaced by Cu, the decagonal phase disappears and the only phase observed is the vacancy ordered phase. In Al70Co15CuxNi15−x when the Cu concentration reaches a value of 10 at.%, the decagonal and crystalline phases coexist.