Pressure Effects on Structural Relaxation of La-Al-(Cu, Ni) Bulk Metallic Glass

In this study, La62.0Al15.7(Cu0.5Ni0.5)22.3 bulk metallic glasses (BMGs) were prepared by copper mold casting method, and the effects of the pressure treatment up to 5.0 GPa at room temperature on structural relaxation were investigated by X-ray diffraction (XRD) and differential scanning calorimeter (DSC). The results showed that structural relaxation occurred with changes of the glass transition temperature (Tg) and the onset of primary crystallization (Tx1). Both increased with increasing of applied pressure up to 4.0 GPa beyond which they decreased. The enthalpy changed at the glass transition temperature regime showed that the reduction of the free volume caused by the HP treatment can be interpreted by the activation volumes of the flow defects. Furthermore, the HP treatment also influenced the crystallization sequence of the BMG.