27Al nuclear magnetic resonance and relaxation was applied to the study of the effects of ball milling upon the long-range order of face-centered cubic Li2 Ni3Al as well as to the subsequent microscopic re-ordering process through annealing. Structural changes due to the mechanical treatment were correlated with the appearance of a strong magnetization in the disordered phase. In the absence of significant Fe contamination, this magnetic property was attributed to the existence of magnetic moments of the order of 0.23μB localized at the Ni sites. 27Al nuclear magnetic resonance spectra in both the ordered and the disordered phase were presented. The random distribution of atoms combined with the magnetic properties in the disordered phase cause a substantial broadening of the 27Alnuclear magnetic resonance line. The linewidth was proportional to the fractional change of disorder and was therefore used to monitor the ordering transformation as a function of annealing time and temperature. The changes of spin-lattice relaxation rates (T1-1) and Knight shifts during transformation were also examined. The overall ordering behavior as observed by nuclear magnetic resonance was described in terms of a stretched exponential for the time dependence of the untransformed fraction, implying a time-dependent transformation rate. The activation energy of the Ni vacancy migration mechanism responsible for the transformation was determined to be E = 1.8eV. The average distance covered by the atoms during the ordering was estimated by means of a simple random-walk model.

NMR Study of Ordering Kinetics in Ni3Al Alloys. Scherrer, P., Dimitropoulos, C., Borsa, F., Rubini, S.: Physical Review B, 1998, 57[17], 10462-9