Atomic Redistribution in a Fe-Cr System in the Course of Mechanical Alloying and Subsequent Annealing

Abstract

Evolution of the structure and atomic distribution in Fe1−xCrx (x = 0.2, 0.3, 0.4 and 0.48) samples in the course of Fe and Cr elemental powder mechanical alloying (MA), as well as during the subsequent isochronous (4 hours) annealing in the 400 °C to 700 °C temperature range, has been studied using 57Fe Mossbauer spectrometry and X-ray diffraction with a focus on the short-range order (SRO). It was established that MA proceeds in one stage for x ≤ 0.3 or three consecutive stages for x > 0.3. The single-stage process is characterized by preferential penetration of Cr into the Fe matrix, while the three-stage process comprises diffusion of Cr into Fe as in the previous case, formation of Cr- and Fe-rich areas, and formation of homogeneous α-Fe(Cr) solid solution. The change in the MA mechanism occurs as Fe is saturated with Cr and is caused by the inversion of the mixing energy sign from negative to positive. For all samples with x ≤ 0.3 annealed at all temperatures and for x > 0.3 annealed at 400 °C, only a small trend toward SRO was observed (SRO parameter 0.3 annealed at temperatures > 400 °C are subjected to thermally induced decomposition, which is accompanied by chromium segregations to the grain boundaries.