Flow Behavior Of Zr₃₅Ti₃₀Cu_8.25Be_26.75 Amorphous Alloy At High Temperature And High Strain Sate

Amorphous alloys have many advantages such as high strength,hardness and elastic limit because of no dislocation and grain boundary defects,and are widely used in aerospace industry,sports goods,medical devices and so on.At present,many amorphous alloys with strong glass forming ability have been developed,and their mechanical and chemical properties at room temperature have been extensively explored.However,the plastic formability and flow behavior of amorphous alloys in the supercooled liquid region at higher temperatures and higher strain rates compression conditions are still unclear.In this paper,Zr₃₅Ti₃₀Cu_8.25Be_26.75 amorphous alloy is selected as the research object,and the following research is carried out systematically.Firstly,the samples of amorphous alloy Zr₃₅Ti₃₀Cu_8.25Be_26.75 were prepared by electric furnace melting and copper die casting,and the samples were tested by X-ray diffractometer?XRD-7000?to ensure that the samples structure were completely amorphous.The glass transition temperature,crystallization temperature and width of the supercooled liquid region of Zr₃₅Ti₃₀Cu_8.25Be_26.75 amorphous alloy were determined by differential scanning calorimetry.Isothermal crystallization tests were carried out on the samples by differential scanning calorimeter,and the crystallization rules of Zr-based amorphous alloys were obtained.It was found that the crystallization incubation time of Zr-based amorphous alloys was more than 20 min at 673 K and below;when the temperature was higher than 673 K,the crystallization incubation time was shortened sharply;when the temperature was 713 K,the crystallization time was shortened to 5.5 min.Based on the temperature and incubation time,the Time-Temperature-Transformation?TTT?curve was established.Secondly,in order to study the flow behavior of Zr₃₅Ti₃₀Cu_8.25Be_26.75 amorphous alloys at high temperature and high strain rate in the supercooled liquid region,Zwick/Roell?Zwick Z020?mechanical property testing machine was used to conduct compression experiments at high temperature?¹.2T_g?and high strain rate(¹0⁰ s^-1).The results show that the flow behavior of Zr₃₅Ti₃₀Cu_8.25Be_26.75 amorphous alloy is sensitive to temperature and strain rate,that is,with the decrease of temperature and the increase of strain rate,the flow stress of amorphous alloy increases monotonously,and its deformation behavior changes from equilibrium Newtonian flow to non-equilibrium non-Newtonian flow.It is also found that the strain rate sensitivity coefficient of amorphous alloys decreases first?minimum 0.06?and then increases?maximum 0.70?with the increase of strain rate,indicating that the superplasticity of amorphous alloys disappears first and then recovers with the increase of strain rate.The main reason is that the larger the strain rate is,the larger the generation rate of the free volume inside the amorphous volume is,but the annihilation rate of the free volume is more stable.Therefore,as the strain rate increases,the residual free volume content of the amorphous first decreases and then increases.The results of differential scanning calorimetry?Perkin-Elmer,DSC-7?and transmission electron microscopy?TEM,TECNAI?show that the trend of free volume change of amorphous alloys is consistent with that of strain rate sensitivity coefficient.Then in order to accurately characterize the influence of temperature and strain rate on the flow stress of amorphous alloy,the constitutive model of high-temperature and high-strain rate compression deformation of amorphous alloys was constructed.Compared with experimental data and model prediction data,it was found that the fitting result of Fictive Stress Model was deviated greatly,and the error was more than 50%.Therefore,the fitting of Maxwell-Pulse constitutive model under high-strain rate compression was carried out.The results show that the predicted values of Maxwell-Pulse constitutive model are in good agreement with the experimental values,and the accuracy is over 90%.In addition,Maxwell-Pulse constitutive model can not only describe the Newtonian flow and non-Newtonian flow of amorphous alloys,but also accurately reflect the stress-strain relationship of amorphous alloys under high temperature and higher strain rate deformation conditions,indicating that the Maxwell-Pulse constitutive model has better applicability when the amorphous alloy is deformed at high temperature and high strain rate.Finally,the flow behavior and constitutive model obtained above are verified by two-cup extrusion experiment and DEFORM-2D finite element simulation.The height of the upper and lower cups predicted by the finite element method is almost the same as the height of the upper and lower cups obtained by the actual experiment.At the same time,the load-stroke curves calculated by the model have good repeatability with the actual load-stroke curves,which proves the accuracy of the constitutive model.Meanwhile,the ratio of upper cup height to lower cup height increases first and then decreases with the increase of strain rate,which is consistent with the rule that the plasticity of amorphous alloy decreases first and then increases with the increase of strain rate,which verifies the accuracy of the flow law of amorphous alloy obtained previously.