Two-phase coexistence region in mechanically alloyed Cu-Fe: An X-ray absorption near-edge structure study

A new technique using the X-ray absorption near-edge structure (XANES) has been developed to simultaneously determine the compositions and phase fract ions of the two coexisting (f.c.c. and b.c.c.) supersaturated solid solutio ns in mechanically alloyed Cu100-xFex (x= 50-80) formed by ball milling und er cryogenic conditions. The XANES analysis indicates that throughout this region the two coexistent phases have almost identical composition, consist ent with that of the overall mixture. This represents a novel two-phase coe xistence representing a region of overlap in solubility rather than the nor mal miscibility gap. A mechanism is proposed to explain the nature of this two-phase region in terms of extended solubility induced by ball milling, t he free energies of the two phases including defect enthalpies, and nucleat ion and growth barriers for the b.c.c.-f.c.c. (and f.c.c.-b.c.c.) transform ation. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. A ll rights reserved.