Thermal stability and crystallisation behavior of newly developed Cu–Zr–Ag–Ti–Ni multicomponent bulk metallic glass

Abstract

A comprehensive understanding of the thermal stability of multicomponent bulk metallic glasses (MBMGs) is imperative for their possible technological applications. In this study, new MBMGs, Cu39Zr42Ag9Ti10 and Cu32Zr39Ag8Ti9Ni12, were developed employing a multilayer perceptron neural network, intelligently expanding the binary Cu50Zr50 BMG. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses were used to confirm the amorphous nature of the as-cast alloys. The crystallisation kinetics of the alloys were investigated using differential scanning calorimetry (DSC) under isochronal conditions at different heating rates coupled with microstructural analyses tools. The thermal attributes suggest that glass transition and crystallisation are more sluggish in the case of Cu32Zr39Ag8Ti9Ni12 compared to Cu39Zr42Ag9Ti10. The local activation energies (Eα) and the Avrami exponent (nα) indicate a diffusion-controlled crystallisation mechanism for both alloys. The nucleation rate of the crystalline phase(s) is relatively lower for Cu32Zr39Ag8Ti9Ni12, indicating sluggish crystallisation. Moreover, the rate of change of nα becomes much slower for Cu32Zr39Ag8Ti9Ni12 MBMG during the later stages of crystallisation owing to higher undercooling and, thus, a higher required driving force for the growth of nucleated phases. The free volume of Cu32Zr39Ag8Ti9Ni12 remains smaller at both room and elevated temperatures, pointing towards its better glass forming ability. XRD and TEM analyses of the crystallised alloys suggested progressively increasing precipitation of the topologically disordered Cu10Zr7 phase from Cu42Zr48Ag10 to Cu32Zr39Ag8Ti9Ni12 MBMG, potentially aiding in its increased thermal stability.