Steady state products in the Fe–Ge system produced by mechanical alloying

Abstract

Prolonged mechanical alloying of elemental blends and mechanical milling of individual intermetallics of the same chemical composition in the Fe–Ge system lead to the same steady state. The phase composition of this steady state was investigated in the entire composition range using a conventional XRD technique. A map reflecting the steady-state phase composition for the different chemical composition was constructed. Mechanical alloying and grinding form products of the following composition (in sequence of increasing Ge content): α (α 1) bcc solid solution, α+β-phase (Fe 2− x Ge), β-phase, β+FeGe(B20), FeGe(B20), FeGe(B20)+FeGe 2, FeGe 2, FeGe 2+Ge, Ge. The incongruently melting intermetallics Fe 6Ge 5 and Fe 2Ge 3 decompose on milling. Fe 6Ge 5 produces a mixture of the β-phase and FeGe(B20) while Fe 2Ge 3 produces a mixture of the FeGe(B20) and FeGe 2 phases. These facts are in good agreement with a model that implies local melting as mechanism for new phase formation during mechanical alloying. The stability of the FeGe(B20) phase, which is also an incongruently melting compound, is explained as a result of the highest density of this phase in the Fe–Ge system.