Anomalous behavior of glass-forming ability and mechanical response in a series of equiatomic binary to denary metallic glasses

Abstract

Herein, we systematically investigated the impact of configuration entropy (CE) on the glass-forming ability (GFA) and mechanical response in a series of equiatomic binary Cu50Zr50 to denary (CuNiBeCoFe)50(ZrTiHfTaNb)50 metallic glasses (MGs) with similar atomic size difference and enthalpy of mixing. Interestingly, the senary (CuNiBe)50(ZrTiHf)50 MG with a medium CE of 1.79R exhibits the maximum GFA among the MGs, which means that higher CE by itself is not a sufficient condition for higher GFA, although it should be a major design parameter according to the confusion principle. The mechanical response analysis was comprehensively performed using nanoindentation test including statistical analysis of pop-in event to elucidate deformation dynamics of shear-avalanches, and the analysis result was compared with the intensive structure data obtained by high energy X-ray scattering analysis. The nanohardness and the Young's modulus (E) in MG with higher CE are shown to outwardly increase which is dominantly due to increased 3-atom connections of cluster polyhedra as well as lower fragility. However, the severe local structural irregularity and the compositional complexity in MG with higher CE promotes the manifestation of relatively chaotic behavior as well as the loss of MG's property inheritance, which results in the unexpected local softening of MG and ultimately modulating the response towards ductile deformation. Thus, the denary MG with the highest CE of 2.30R exhibits an abnormally low incremental rate in the cut-off values of strain burst size as well as measured E. Consequently, it can be concluded that the CE could be one of the crucial factors in designing an MG to alter its characteristics towards achieving desirable properties such as high GFA and enhanced plasticity. ？ 2019