Fabrication and mechanical properties of bulk nanocrystalline intermetallic Mg2Si

Bulk nanocrystalline Mg2Si intermetallics (nano-Mg2Si) was prepared by using mechanically activated solid-state reaction plus hot-pressing. The influences of preparation conditions on phase formation, microstructures and mechanical properties of nano-Mg2Si were examined. The results indicated that impurity iron was favorable to toughness of bulk nano-Mg2Si samples. However, the iron was inclined to react with Si to form FeSi phase at the temperatures >= 480 degrees C, which will degenerate toughness of bulk nano-Mg2Si. Proper over-stoichiometry of Mg was found to be imperative in obtaining monolithic nano-Mg2Si. Although hot-pressing (under high pressure) at higher temperatures can lead to higher densification, the toughness of the samples hot-pressed at very high temperatures (T > 450 degrees C) degraded, which can be mainly ascribed to the formation of small amounts of FeSi and MgO phases. The fracture toughness of the high-density (relative density D similar to 98%) monolithic nano-Mg2Si (grain size d similar to 54 nm) reached 1.67 MPa m(1/2), which is superior to that of its conventional counterpart. (C) 2007 Elsevier B.V. All rights reserved.