Ordering Kinetics and Diffusion in Some L12 Alloys

Abstract

AbstractA comparison is made of, ordering kinetics for Cu3Au, (Tc = 388 ° C), Ni3Mn (Tc = 500° C) Ni3Fe (Tc = 517°C) and Ni3Al (Tc = 1450 ° C), which all form the L12 superlattice, and these kinetics are correlated with diffusion data for the same alloys. Comparing different alloys, it is shown that for a fixed relaxation time for the establishment of order, the lower is the self-diffusivity, Ds, of the slowest-diffusing species, the higher the critical temperature, Tc, for the first appearance of order. Ni3A1, in particular, has an estimated Ds of about 5 orders of magnitude lower, on average, than the three other alloys. The implications of this inverse relation between Tc and Ds are discussed in relation to published models for diffusion in ordered alloys and ordering kinetics.