1991 Volume 32 Issue 5 Pages 438-444
The annealing process of a Cu-39.2 at%Pt alloy has been studied by X-ray powder diffraction and electron microscopy. The alloy was first annealed at 853 K to promote ordering to L11, followed by annealing at various temperatures within the (A1+L11) region. It is found that the annealing process has different ways below and above a critical temperature (Tc). When the annealing temperature Ta is below Tc, A1 phase precipitates at boundaries between variants of L11 to form a coexisting state of (A1+L11). For Ta>Tc, L11 firstly disorders to A1, and subsequently L11 precipitates in the matrix of A1. The critical temperature corresponds thermodynamically to an order-disorder transformation temperature at which the free energy of A1 is equal to the one of L11. The annealing processes observed are explained by a simple approach using diagrams for free energy vs. degree of order and vs. composition.
