Phases formation during heating of Mg-Cu-Ag-Y bulk metallic glasses

DSC and in-situ neutron diffraction have been used in order to find the phases formed under various heating treatments in the vicinity of the glass transition for Mg-based bulk metallic glasses (BMG). The first phase to crystallize in the Mg58.5Cu30.5Y11 alloy, when the sample is hold at Tg + 20 K, is Mg2Cu and a nanocrystallized phase. During continuous heating of the same sample, the main phases to crystallize are Mg2Cu, MgY and Cu2Y. The alloy Mg55.5Cu28.5Ag5Y11 has the best GFA parameters observed for Mg-based BMG (ΔT = 54o and γ = 0.415) and presents a single event for crystallization. The phases formed by holding the sample at Tg + 20 K are the same than observed for the alloy without silver (Mg2Cu and nanophase). During continuous heating of this sample the same phases as previously observed appear but with Ag3Mg as extra phase. If ternary phases are present, they could correspond to tiny lines not refined, but they appear with a very low intensity. Mg2Cu and Cu2Y produce the main intensity lines. The appearance of nanocrystals during crystallization in the glass transition region could be at the origin of the plasticity observed in these alloys.