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

Abstract A new technique using the X-ray absorption near-edge structure (XANES) has been developed to simultaneously determine the compositions and phase fractions of the two coexisting (f.c.c. and b.c.c.) supersaturated solid solutions in mechanically alloyed Cu 100− x Fe x ( x =50–80) formed by ball milling under cryogenic conditions. The XANES analysis indicates that throughout this region the two coexistent phases have almost identical composition, consistent with that of the overall mixture. This represents a novel two-phase coexistence representing a region of overlap in solubility rather than the normal miscibility gap. A mechanism is proposed to explain the nature of this two-phase region in terms of extended solubility induced by ball milling, the free energies of the two phases including defect enthalpies, and nucleation and growth barriers for the b.c.c.–f.c.c. (and f.c.c.–b.c.c.) transformation.