Phase separation and sample size independence of fracture strength for (Mg0.585Cu0.305Y0.11)95Be5 bulk metallic glass

An (Mg0.585Cu0.305Y0.11)95Be5 bulk metallic glass (BMG) with high strength was fabricated by conventional Cu-mold casting method. The phase structure, thermal stability and microstructure of the BMG were investigated by using X-ray diffraction, differential scanning calorimetry, transmission electron microscopy and scanning electron microscopy. The results show that the quaternary (Mg0.585Cu0.305Y0.11)95Be5 BMG with 3 mm in diameter exhibits obvious glass transition Tg of 429 K and a wide supercooled liquid region ΔTx of 53 K. Meanwhile, the phase-separated regions characteristic of Cu–Y–Be glass containing nanometer CuY crystals are heterogeneously distributed in the Mg–Cu–Y glassy matrix in the as-cast samples. Under uniaxial compressive loading, the samples with 1, 2 and 3 mm in diameter show high strength up to 959, 955 MPa and 954 MPa, respectively. The sample-size independence of fracture strength was for the first time found in the Mg-TM–RE metallic glasses. The effects of Be addition on phase separation and mechanical properties for Mg–Cu–Y alloy system were discussed.