Magnesium silicide (Mg2Si) is a promising thermoelectric(TE) material with the advantages of lightweight, abundance of its constituent elements in nature, and high power generation efficiency at about 873 K. This material is expected to apply automobile application to reduce waste heat, however improvement of mechanical properties is required for practical applications. Especially, improvement of fracture toughness without reduction of TE properties becomes important issue. The purpose of this study is to improve of fracture toughness of Mg2Si by refinement of Mg2Si matrix and addition of secondary phases (Si3N4). In case of fine Mg2Si specimen, Young's modulus and fracture toughness are increased with decreasing grain size. They are reached at 118 GPa and 2.0 MPa√m, respectively. Mechanical properties of Mg2Si are also improved by incorporation of Si3N4 particles. These experimental results suggest that addition of secondary phase and refinement of grain size are effective to enhance mechanical properties of Mg2Si.
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