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

Abstract

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 Mg 58.5Cu 30.5Y 11 alloy, when the sample is hold at T g + 20 K, is Mg 2Cu and a nanocrystallized phase. During continuous heating of the same sample, the main phases to crystallize are Mg 2Cu, MgY and Cu 2Y. The alloy Mg 55.5Cu 28.5Ag 5Y 11 has the best GFA parameters observed for Mg-based BMG (Δ T = 54° and γ = 0.415) and presents a single event for crystallization. The phases formed by holding the sample at T g + 20 K are the same than observed for the alloy without silver (Mg 2Cu and nanophase). During continuous heating of this sample the same phases as previously observed appear but with Ag 3Mg as extra phase. If ternary phases are present, they could correspond to tiny lines not refined, but they appear with a very low intensity. Mg 2Cu and Cu 2Y 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.