A nano τ3 vacancy-ordered phase in the Al-Cu-Ni alloy system was synthesized with a composition close to Al70Cu15Ni15 by mechanical alloying a mixture of elemental powder in a high-energy ball mill by varying milling time from 10 to 100 hours. The stability of nano-crystalline τ3 vacancy-ordered phase was studied under thermal annealing in vacuum as well as in air. The X-ray diffraction and transmission electron microscopy techniques were employed for characterization of the milled and annealed samples. The powder after 100 h of milling was found to contain mostly nano τ3 phase with the partial ordering, and with crystallite sizes in the range of 10-20 nm along with a lattice strain of ~0.67 %. The milled powder, after annealing in vacuum at 700C for 60 h, revealed the formation of a strain-free and ordered τ3 phase with a crystallite size of 80 nm, indicating grain coarsening. It was interesting to note that the milled powder annealed in air at 700C for 60 h showed the formation of (Cu,Ni)Al2O4 type spinel phase with the lattice parameter of 8.1 Å and the lattice strain as 0.52 %. The average grain size of spinel phase was found to be ~ 40 nm.

Stability of Mechanically Alloyed Vacancy Ordered Phase in Al70Cu15Ni15 Alloy during Annealing. T.P.Yadav, N.K.Mukhopadhyay, R.S.Tiwari, O.N.Srivastava: Journal of Physics - Conference Series, 2010, 226[1], 012033