204 Solid-State Synthesis of Mg_2Si Intermetallic Compound via Powder Metallurgy Process

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The solid-state synthesis of Mg_2Si intermetallic by Powder Metallurgy (P/M) processing has been discussed in this study. Fist of all, the influences of the particle characteristics of input raw materials, such as Mg and Si powder, and the compacting conditions on the behavior in forming Mg_2Si were investigated. The surface oxide films of raw powder, in particular MgO, causes to prevent the reaction between Mg and Si because of its thermal stability. After destroying such oxide films, the increase of the contacting area of both powders is effective on the progress of the reaction of Mg with Si to synthesize Mg_2Si. Considering these results, bulk mechanical alloying (BMA) process, which assists to refine the elemental mixture powder and to break the surface oxide films by cyclic plastic works such as extrusion and compaction processes, was employed. For example, when using Mg/Si composite powder via BMA process with the cycle number over 100 cycles, the temperature in synthesizing Mg_2Si is about 473K, and is shifted to the extremely low temperature range. Via route of BMA over 300cyles on Mg-33.33mol%Si mixture powder, Mg_2Si fine particles of 30-100nm in diameter were in-situ formed during BMA process.
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