On Cr and Si Redistribution in (Fe,Cr,Si)75C25 Nanocomposites: Mechanosynthesis and Annealing

Abstract

Phase analysis of nanocrystalline alloys with a composition of (Fe\(_{{0.97-x}}\)Cr_xSi_0.03)₇₅C₂₅ (x = 0.05 and 0.10) in the states after mechanical synthesis (MS) and subsequent annealings was performed by X-ray diffractometry, Mössbauer spectroscopy, and magnetic measurements. Mechanical synthesis forms ~46–58 vol % X-ray amorphous phase (XAP), ~30–39 vol % χ-carbide, and only ~9–11 vol % cementite. Mechanically synthesized carbides are doped not only with chromium, but also with silicon. During annealing in the temperature range T_ann = 400–500°C, all silicon is released from carbides and dissolved in ferrite. Crystallization of the XAP occurs in two stages. The first stage (T_ann < 500°C) is characterized by the formation of carbides from the Si-depleted regions of the XAP. At the second stage (T_ann ≥ 500°C), the residual XAP decomposes into ferrite and cementite with a higher Cr concentration than in cementite formed both at the first stage of XAP crystallization and during MS. Further increase in T_ann leads to a more uniform distribution of chromium atoms in cementite.