Viscoplastic Forming of Mg Bulk Metallic Glasses in the Supercooled Liquid Region

Abstract

The Mg-Cu-rare earth (RE) alloys are produced under the form of amorphous cylindrical rods and characterized by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Their capacity to be deformed in the supercooled liquid regions (SLRs) is studied. In the SLRs, crystallization can occur and strongly affect the viscoplastic forming conditions. Consequently, the thermal stabilities of the glasses are studied, in particular in the case of a Mg-Cu-Gd glass for which the kinetics of crystallization are quantified and the associated populations of crystallites identified. By appropriate heat treatments, various fractions of crystallites are thus produced and the effects of crystallization on the viscoplastic properties in the SLR are discussed in relation to mechanical models developed for materials containing rigid inclusions dispersed in a viscous medium. Finally, the possible effect of deformation on crystallization kinetics is also considered.

High temperature deformation in a lanthanum based bulk metallic glass showing a pronounced secondary relaxation

“…Values of E act close to 300 kJ/mol can be estimated. This value is close to values reported for metallic glasses displaying similar glass transition temperatures, like for instance Mg-based bulk metallic glass [41] and remains lower than the activation energies measured for metallic glasses with significantly higher glass transition temperatures [28]. In other words, the activation energy E act appears to be not significantly influenced by the presence of β relaxation but more correlated to the glass transition temperature.…”

High Temperature Forming Maps of Various Bulk Metallic Glasses

“…The three following figures concern the Mg based BMG but they are typical of the procedure used to determine the thermoforming window for a given BMG. Additional information concerning the high temperature deformation of the investigated glasses can be found elsewhere [6,11,12]. Fig.…”