THE GROWTH OF OMEGA-PHASE INCLUSIONS IN TI-20 AT PERCENT MO AND THE COMPETITION BETWEEN ELASTIC AND SURFACE ENERGIES

The growth of omega-inclusions during the annealing of Ti-20 at.% Mo at temperatures below 500-degrees-C was studied by small-angle X-ray scattering (SAXS). A time-scaling behavior of the structure function was observed, but the scaling function F(x) appeared to be different from the "universal" shape found for many decomposing binary systems. To explain this effect, a trapping of molybdenum at the surface of the omega-inclusions is proposed, which might be due to the strong lattice misfit between the omega-inclusion and the cubic matrix. Furthermore, the inclusion size R(t) was found to increase, in a first step, as R proportional t1/3 with annealing time t, but then to stabilize at a constant value R almost-equal-to 75 angstrom. This is interpreted as a coarsening process, progressively hindered by attractive elastic interactions between omega-precipitates.