Concentration distribution of elements and variation in phase composition during solid-solution decomposition in Fe-Cr-Co alloy

Abstract

In the present work, we analyze the changes in chemical and phase composition in the decomposition of metastable supercooled hightemperature α solid solution in the alloy Fe + 31 wt % Cr + 23 wt % Co. Permanent magnets based on Fe-Cr-Co alloys are still widely used in industry, although they cannot match the properties of the latest alloys of rareearth metals with 3d metals. The explanation for their con� tinued use is that Fe-Cr-Co alloys combine satisfac� tory physicochemical and mechanical properties with low cost. In Fe-Cr-Co alloys, a highly coercive state arises as a result of the decomposition of the α solid solution into two amorphous phases: α1 and α2 (1). Moreover, some evidence suggests that Fe-Co-Cr alloys treated in the highly coercive state contain three magnetic phases: ferromagnetic, antiferromagnetic, and super� paramagnetic (2, 3). The coexistence of ferromagnetic and antiferromagnetic phases in magnetically ordered systems is the fundamental condition for the appear� ance of anomalies in most physical properties. Exam� ples include the anomalies of thermal expansion noted in Fe-Co-Cr alloys in (3). The contradictory data regarding the phase state of Fe-Co-Cr alloys prompts further study. The decomposition of the supersaturated solid solution is simulated by the Monte Carlo method, using the Metropolis criterion. The interaction energy is calculated by means of Material Studio 3.2 software, selected on the basis of the results in (4). The simula� tion of the isothermal decomposition of Fe-Cr-Co alloys was described in (5, 6). The alloy composition is chosen on the basis of detailed data regarding the for� mation of its phase state and microstructure (1, 7). The algorithm employed permits the construction of distributions of iron, chromium, and cobalt in the region considered. As an example, the chromium and cobalt distributions in the final microstructure after decomposition at 660°C are shown in Fig. 1. In contrast to the chaotic distribution of chromium and cobalt in the initial microstructure, the amplitude and wavelength of the concentration distribution are