Phase-separation kinetics of a multicomponent alloy

Phase separation kinetics of multicomponent 350-grade maraging steel has be en investigated on both recrystallized as well as cold-worked specimens by small-angle x-ray scattering, wide angle x-ray scattering, and transmission electron microscopy at two different temperatures, viz. 430 degrees C and 510 degrees C, for different aging times. Unlike previous observations, at both the temperatures, dynamical scaling behavior is observed at the early stages of phase separation accompanied by diffuse interface of the secondar y phases. Porod exponents have been found to be greater than 4. At late sta ges, the precipitate-matrix interface becomes sharp - the Pored exponent is close to 4 but clear deviation from the dynamical scaling behavior is evid ent. At 430 OC, the phase separation is attributed to the formation of an o rdered omega phase through a mechanism involving chemical ordering and the omega-like lattice collapse in the bcc structure. Time (t) dependent popula tion averaged precipitate radius follows t(1/5) power law indicating cluste r diffusion mechanism of Binder-Stauffer type for the entire range, 30 min- 72 h, of aging time. At 510 degrees C,the phase separation is attributed to the formation of Ni-3(Ti,Mo) with DO24 structure through the process of nu cleation and growth. Average precipitate radius follows t(1/3) Lifshitz-Sly ozov power law for the entire range, 5 min-18 h, of aging time. The system, despite being multicomponent and complex, appears to follow two distinct t ime-temperature-transformation corves. As far as the effect of cold work on phase-separation behavior is concerned, it has been found that cold work f acilitates the growth of the precipitates. Also, it narrows down the size d istribution and enforces strong spatial correlation of the precipitates. Co ld working the material is found to be detrimental to the dynamical scaling behavior.