  Ordering processes in fcc-alloys with composition A_3B (like Cu_3Au, Cu_3Pd,
CoPt_3 etc.) are investigated by Monte Carlo simulation within a class of
lattice models based on nearest-neighbor (NN) and second-neighbor (NNN)
interactions. Using an atom-vacancy exchange algorithm, we study the growth of
ordered domains following a temperature quench below the ordering spinodal. For
zero NNN-interactions we observe an anomalously slow growth of the domain size
L(t) \sim t^\alpha, where \alpha \sim 1/4 within our accessible timescales.
With increasing NNN-interactions domain growth becomes faster and \alpha
gradually approaches the value 1/2 as predicted by the conventional
Lifshitz-Allen-Cahn theory.
