Composition Design Of Metallic Glasses Based On Compounds With Low Melting Entropy

Elevating the glass forming ability（GFA）of metallic glasses and developing novel metal glass systems have long been focal points of interest for researchers.Elucidating the roles of thermodynamics and kinetics in glass formation facilitates the identification and preparation of suitable glass-forming materials for various scenarios.Studies have shown that glass formation is determined by thermodynamics and dynamics Thus,comprehending the interplay between thermodynamics and kinetics,and identifying crucial and practical criteria for assessing glass forming ability will undoubtedly provide a fresh perspective on the understanding of glass formation.In this study,we first selected the Zr₂Ni-Ti₂Ni pseudo-binary system,known for its multiple eutectic and intermetallic compound features,as the subject of investigation.The influence of thermodynamic and kinetic factors on glass formation was explored,with the thermodynamic parameter focusing on the melting entropyΔS_m and the kinetic parameter on the liquidus viscosityη_Tl.The results revealed that within the Zr₂Ni-Ti₂Ni system,compositions exhibiting excellent glass forming ability possess low melting entropy and high liquidus viscosity,with an increase in melting entropy accompanying a decrease in viscosity.The viscosity data obtained by different test methods are unified,a strong correlation between melting entropy and liquidus viscosity in metallic glass systems was unveiled.This correlation manifests as an increase in glass-forming ability with higher viscosity and decreased melting entropy.This study demonstrated that both eutectic compositions and intermetallic compounds with low melting entropy exhibit high glass forming ability,thus underscoring the significance of thermodynamics in glass formation.Expanding the study to encompass various glass-forming systems,including small molecular glasses,network glasses,and oxide glasses,and utilizing the reduced melting entropy parameterΔS_m/beads expressing molecular structural information,revealed the persistent strong correlation between reduced melting entropy and liquidus viscosity.In order to further explain the phenomenon that the GFA of the compounds in the Zr₂Ni-Ti₂Ni system is better than that near the eutectic point,the fundamental characteristics of intermetallic compound glasses were investigated.Several binary systems,including Cu-Zr,Ni-Zr,and Cu-Hf,were systematically studied,showing that compounds with excellent glass forming ability exhibit low melting entropyΔS_m,more negative excess melting entropyΔS_m-exc,and low enthalpy of formationΔH_f as thermodynamic features.Dynamic analysis through molecular dynamics simulations was conducted to study the kinetic parameters of intermetallic compound glass transitions.The results indicated that well-formed intermetallic compound glasses possess relatively slow melt dynamics.The disparity in the dynamic relaxation timesτbetween Cu₅₀Zr₅₀ and Cu₁₀Zr₇ in the Cu-Zr system,despite their corresponding GFA characteristics,highlights the undeniable role of thermodynamics in glass formation.A comprehensive comparison of the critical shear rate R_v and the thermodynamic parameters such as melting entropyΔS_m,enthalpy of fusionΔH_m,and melting temperature Tm confirmed that the influence of low melting entropy on intermetallic compound glass formation is fundamental,identifying it as a characteristic feature of intermetallic compounds that facilitates glass formation.Relying on the key role of melting entropy in glass formation and the basic characteristics of compound metallic galsses,intermetallic compounds were chosen as initial materials for metallic glass composition design,and a new scheme of metallic glass design was established.For instance,utilizing the intermetallic compounds Cu₅₀Zr₅₀ and Cu₁₀Hf₇,known for their low melting entropy characteristics,as initial phases,the glass composition design was carried out by considering the lever rule with balanced weight factors based on low melting entropy,low excess melting entropy,and low enthalpy of formation.The results showed that the ternary alloy Cu_52.1Zr_38.05Hf_9.85,designed based on excess melting entropy,possessed a composition range and GFA highly similar to the best-reported glass forming material Cu₅₀Zr₄₀Hf₁₀.With an increase in the amount of the parent alloy,incorporating the compound Cu₁₀Zr₇,which also features low melting entropy,led to the discovery of a new ternary composition,Cu_54.85Zr_39.34Hf_5.81,exhibiting outstanding GFA within the ternary system,with a critical size approaching 1.5 mm.This design approach significantly improved the efficiency of glass composition determination for achieving compositions with excellent GFA compared to traditional metal glass composition design.In order to elucidate the underlying mechanisms of low melting entropy guiding glass formation,the research focus has been further directed towards the vibrational entropy and excess vibrational entropy characteristics of crystalline materials.Taking intermetallic compounds in the Cu-Zr system as the research subject,molecular dynamics simulation methods were employed to investigate the vibrational entropy characteristics of various intermetallic compounds.This study revealed the correlation between the glass-forming ability（GFA）,melting entropy,and the crystalline vibrational entropy and excess vibrational entropy of intermetallic compounds,highlighting the influence of high vibrational entropy（or low-frequency atomic vibration modes）on the formation of amorphous systems.The present study establishes a direct relationship between the crystalline structural features of materials and GFA,proposing vibrational entropy as a new criterion for glass formation.