Thermodynamic And Kinetic Behaviors Of TiZr-Based Amorphous Alloys

Amorphous alloys have been widely noticed in the field of engineering structural materials with promising applications due to their excellent mechanical properties such as high hardness,high elastic limit and high specific strength,which are limited by their critical casting dimensions.Amorphous alloys are thermodynamically substable,so it is important to improve the thermal stability and retard the crystallization rate of amorphous alloys to promote the application of amorphous alloys.In this paper,the glass formation ability,thermal stability and crystallization kinetics of TiZr-based alloy are investigated by thermodynamic and kinetic methods.In this paper,Ti32.8Zr30.2Cu9Ni5.3Be22.7 alloy is used as the basis,and different alloy systems are formed by adjusting the types and proportions of added elements.The bulk alloy specimens were prepared by the copper mold casting method.The structure and properties of the alloy specimens were characterized by X-ray diffractometer,Differential Scanning Calorimetry,Transmission Electron Microscope and universal mechanical testing machine,respectively.The research content and the results obtained of this paper include:The glass forming ability of Ti32.8Zr30.2Cu9Ni5.3Be22.7 alloy and its mechanism were investigated.The results show that the crystallization driving force ΔGl-x of Ti32.8Zr30.2Cu9Ni5.3Be22.7 alloy is only 1.6 kJ/mol and the brittleness index is D*=45.2,which is an amorphous alloy with ultra-high glass-forming ability.The presence of a strong short-and medium-range ordered structure in the supercooled liquid of the alloy indicates that the ultra-high glass-forming ability is the result of the synergistic effect of thermodynamics and kinetics.The kinetic behavior of the supercooled liquid phase and the high-temperature melt was analyzed by the Angell brittleness concept and the kinetic equations,which revealed the existence of a "fragile-strong"transition in the alloy.Based on the Ti32.8Zr30.2M14.3Be22.7 alloy,the Ti32.8Zr30.2Cu9M5.3Be22.7(M=Fe,Co,Ni),Ti32.8Zr30.2Fe9M5.3Be22.7(M=Co、Ni、Cu)and Ti32.8Zr30.2(FeCoNiCu)14.3Be22,7 series alloys were formed by changing the type and proportion of added elements and replacing each other with Cu,Fe,Co and Ni elements of almost the same atomic size.The effect of microalloying on the glass forming ability of amorphous alloy was investigated.The results show that microalloying can not only increase the energy barriers that need to be overcome for the nucleation and growth of the crystalline phase in Ti32.8Zr30.2M14.3Be22.7 alloys,making the process of nucleation and growth of the crystalline phase more difficult,but also improve the bonding force between the atoms of the constituent elements and give the alloy a relatively stable supercooled liquid phase.The Ti63-xZrxCu9Ni5.3Be22.7 series alloy compositions were obtained by adjusting the atomic ratios of Ti and Zr elements on the basis of Ti32.8Zr30.2Cu9Ni5.3Be22.7 alloy.The glass forming ability of Ti63-xZrxCu9Ni5.3Be22.7 series alloys was explored using thermodynamics and crystallization kinetics.The results show that when the atomic ratio of Ti and Zr elements is infinitely close to 1:1,the values of crystallization activation energy Ex and Ep of this series of alloys reach the maximum and are higher than the glass transition activation energy Eg.Therefore,when the atomic ratio of Ti and Zr elements in the alloy is infinitely close to 1:1,this series of amorphous alloys has the most excellent glass formation ability.The characteristic temperature parameters and the heating rate basically show a positive correlation trend,indicating that the glass transition and crystallization processes of Ti63-xZrxCu9Ni5.3Be22.7 alloys are affected by the heating rate and show obvious kinetic characteristics.The effect of post-treatment on the glass transition and mechanical properties of Ti32.8Zr30.2Cu9Ni5.3Be22.7 alloy was investigated by annealing treatment.The intrinsic relationships between the thermal stability and crystallization kinetics of the as-cast alloy and the alloy after the annealing treatments were investigated.The results show that the thermomechanical stability of Ti32.8Zr30.2Cu9Ni5.3Be22.7 alloy is significantly enhanced after heat treatment,indicating that annealing treatment can improve the thermomechanical stability of amorphous alloys.As for the crystallization kinetics,the glass transition activation energy of Ti32.8Zr30.2Cu9Ni5.3Be22.7 alloy was significantly reduced after annealing and gradually increased with the increase of annealing time,indicating that different annealing treatment conditions can lead to different glass transition changes.As for the mechanical properties,the compressive strength of Ti32.8Zr30.2Cu9Ni5.3Be22.7 alloy increased with the increase of annealing time.The elastic modulus,Young’s modulus and shear modulus also increased to different degrees,with the increase of elastic modulus reaching 1.2%,shear modulus reaching 7.6%and Young’s modulus reaching 7%.The trend of positive correlation between the characteristic temperature parameters and the heating rate indicates that the glass transformation and crystallization processes of both as-cast and annealed Ti32.8Zr30.2Cu9Ni5.3Be22.7 alloys are influenced by the heating rate,showing obvious kinetic properties.