TIME-EVOLUTION OF LONG-RANGE ORDERING IN CUAUPD TERNARY ALLOYS

Time-evolution of L1(0)-type ordering in CuAuPd ternary alloys at 573 K has been studied in terms of change in long-range order (LRO) parame ters S-i's determined experimentally by an electron diffraction techni que IKL-ALCHEMI. The results clearly show that the ordering rates are different among the three elements. In alloys of Cu50Au35Pd15 and Cu50 Au25Pd25, the LRO parameters of three elements S-i's are enhanced mono tonically with lime, showing inequality \S-Au\ > \S-Cu\ > \S-Pd\ in th e early stage, but \S-Pd\ greater than or equal to \S-Cu\ greater than or equal to \S-Au\ in the late stage. When the Cu content deviates fr om 50 at% to 45 at%, such as in Cu45Au40Pd15 and Cu45Au30Pd25, S-Au on ce increases and then slightly decreases after reaching a peak, while S-Pd and S-Cu continuously approach the equilibrium values. The oversh ooting of S-Au disappears in a less Cu-content alloy of Cu42.5Au42.5Pd 15. The master equation approach has been employed to understand the k inetic behavior as a function of the ordering energies V-ij's, the mob ilities of atoms W-i's and alloy composition. The ordering kinetics in CuAuPd alloys is thoroughly explained in terms of V-CuPd > V-CuAu > V -AuPd, and W-Cu, W-Cu > W-Pb.