  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
Al70 Co15Ni15 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 (XRD),
Scanning and transmission electron microscopy (SEM & TEM). With an increase in
Cu content in the melt spun Al70 Co15Cux Ni15-x (x=0 to 15) alloys, the
relative amount of the decagonal phase decreased up to 10 at% of Cu. At this
composition the quaternary alloy showed the coexistence of decagonal
quasicrystal and superstructure of tau 3 vacancy ordered crystalline phases.
The decagonal phase containing Cu showed more disordering compared to Al-Co-Ni
alloys. The implication of the structural / microstructural changes due to Cu
substitution in stable decagonal quasicrystal will be discussed
