On the evolution of quasicrystalline and crystalline phases in rapidly quenched Al-Co–Cu–Ni alloy

The occurrence of stable decagonal quasicrystalline phase in Al–Co–Ni and Al–Cu–Co alloys through conventional solidification is well established. Earlier, we have studied the effect of Cu substitution in place of Co in the Al70Co15Ni15 alloy. Here we report the structural/micro-structural changes with substitution of Cu for Ni in rapidly solidified Al–Co–Ni alloys. The melt spun ribbons have been characterized using X-ray diffractometry, scanning and transmission electron microscopy. With an increase in Cu content in the melt spun Al70Co15CuxNi15−x (x = 0–15 at.%) alloys, the relative amount of the decagonal phase decreased up to 10 at.% of Cu. At this composition, the quaternary alloy showed the co-existence of decagonal quasicrystal and superstructure of τ3 vacancy ordered crystalline phases. The decagonal phase containing Cu showed more disordering than Al–Co–Ni alloys. The implication of the structural and microstructural changes due to Cu substitution in stable decagonal quasicrystals will be discussed.