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 Al 70 Co 15 Ni 15 . Compositions corresponding to Al 70 Co 15-x Cu x Ni 15 and Al 70 Co 15 Cu x Ni 15-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 Al 70 Co 15-x Cu x Ni 15 , when all of the Co is replaced by Cu, the decagonal phase disappears and the only phase observed is the vacancy ordered phase. In Al 70 Co 15 Cu x Ni 15-x when the Cu concentration reaches a value of 10 at.%, the decagonal and crystalline phases coexist.