Mg-based Metallic Glass Composites Research Articles

In situ formation of crystalline flakes in Mg-based metallic glass composites by controlled inoculation

In situ bulk metallic glass (BMG) composites generally contain a crystalline phase(s) that forms throughout the amorphous matrix during cooling from the melt. The presence of the crystalline phase in these materials is known to improve both ductility and toughness. In this study the nucleation and growth behaviour of crystalline α-Mg flakes during casting of a series of Mg–Cu–Y–Zn glass forming alloys were investigated. It was demonstrated that the α-Mg phase nucleates preferentially on the surface of micron-sized yttria (Y2O3) particles that form in the melt during casting and subsequently grow in preferential crystallographic directions to generate an intimate distribution of interwoven flakes throughout the amorphous matrix. High resolution transmission electron microscopy revealed that a thin (∼5nm) intermediate Cu layer forms at the particle–flake interface resulting in full coherency with both the particle and flake, thereby resulting in well-defined orientation relationships. The formation of this intermediate layer is argued to be the necessary precursor for nucleation of Mg flakes at the Y2O3 particles in a manner similar to that found for the preferential nucleation at TiB2 particles in conventional Al alloys. The overall effect of this intermediate layer is a reduction in the interfacial energy between the particle and nucleus, thereby lowering the thermodynamic barrier for nucleation. In general terms, inoculation controlled formation of a crystalline phase throughout an amorphous matrix in selected glass forming compositions may be a viable means of generating the desired two phase structure for generating high strength BMG composites exhibiting suitable ductility.

High-Strength Mg-Based Bulk Metallic Glass Composites with Remarkable Plasticity

Abstract The paper presents a novel porous, ductile, V particles reinforced, Mg-based metallic glass composite, exhibiting superior mechanical performance with up to 10 % compressive strain and 1100 MPa stress at room temperature. Indentation tests show that the addition of V particles can improve significantly the plastic deformation ability of the glass composites in local regions around the particles. Furthermore, during deformation process, the highly localized shear-banding of the infiltrated glassy matrix within the porous V particles induces an increase in temperature in local regions, where the dilating and softening behavior happen. The heated V particle regions become more effective “sites” for the initiation and arrest of shear bands in the surrounding amorphous matrix. We suggest that porous ductile particles might therefore preferably be used to toughen amorphous materials with stubborn brittleness.