Time-evolution of long range ordering in CuAuPd ternary alloys

Time-evolution of L1₀-type ordering in CuAuPd ternary alloys at 573 K has been studied in terms of change in long-range order (LRO) parameters S_i's determined experimentally by an electron diffraction technique IKL-ALCHEMI. The results clearly show that the ordering rates are different among the three elements. In alloys of Cu₅₀Au₃₅Pd₁₅ and Cu₅₀Au₂₅Pd₂₅, the LRO parameters of three elements S_i's are enhanced monotonically with time, showing inequality |S_Au| > |S_Cu| > |S_Pd| in the early stage, but |S_Pd| ≥ |S_Cu| ≥ |S_Au| in the late stage. When the Cu content deviates from 50 at% to 45 at%, such as in Cu₄₅Au₄₀Pd₁₅ and Cu₄₅Au₄₀Pd₁₅, S_Au once increases and then slightly decreases after reaching a peak, while S_Pd and S_Cu continuously approach the equilibrium values. The overshooting of S_Au disappears in a less Cu-content alloy of Cu_42.5Au_42.5Pd₁₅. The master equation approach has been employed to understand the kinetic behavior as a function of the ordering energies V_ij's, the mobilities 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_Au > W_Pd.