Study On Superplasticity And Crystallization Kinetics Of Cu-Zr-Al Based Amorphous Alloys

Amorphous alloys have great potential for application in many fields because of their excellent and unique properties.Cu-Zr based amorphous alloys have excellent properties such as high glass forming ability,high thermal stability and so on.However,the room temperature brittleness and strain softening of amorphous alloys limit its application in the engineering field,and molding of amorphous alloys by superplasticity can effectively develop its application value.To achieve the superplastic processing of amorphous alloys,the deformation rules of amorphous alloys in the supercooled liquid region should be mastered,and the structural changes and performance changes of amorphous alloys in the process of environmental heat and external force should be effectively controlled.In this article,the deformation behavior of(Cu₄₃Zr₄₈Al₉)₉₈Y₂ bulk amorphous alloys in supercooled liquid region was studied by high temperature compression test.The effects of temperature and strain rate on the deformation behavior of bulk amorphous alloys were analyzed.The effects of different deformation conditions on the microstructure of(Cu₄₃Zr₄₈Al₉)₉₈Y₂ amorphous alloys were analyzed by X ray diffraction?XRD?and transmission electron microscopy?TEM?,and the effects of superplastic deformation on the mechanical properties and thermal properties of amorphous alloys were systematically studied.The thermodynamics of(Cu₄₃Zr₄₈Al₉)_?100-x?Y_x?x=1,2,3?amorphous alloys were tested by differential scanning calorimetry.And the non-isothermal and isothermal crystallization kinetics of(Cu₄₃Zr₄₈Al₉)_?100-x?Y_x?x=1,2,3?amorphous alloys were calculated and analyzed.The study of superplastic deformation behavior of(Cu₄₃Zr₄₈Al₉)₉₈Y₂ amorphous alloys shows that brittle fracture occurs when the deformation temperature of(Cu₄₃Zr₄₈Al₉)₉₈Y₂amorphous alloy is 713 K and the strain rate is>5×10^-33 s^-1.The alloy presents a different state in different deformation conditions,and the‘dividing line'is the boundary between the deformation conditions of the Newtonian flow and the non-Newtonian flow state.When the temperature and the strain rate are above the‘dividing line',the(Cu₄₃Zr₄₈Al₉)₉₈Y₂ amorphous alloys are in the state of non-Newtonian flow.And when the temperature and the strain rate are below the‘dividing line',the(Cu₄₃Zr₄₈Al₉)₉₈Y₂ amorphous alloys are in the state of Newtonian flow.(Cu₄₃Zr₄₈Al₉)₉₈Y₂ alloys have more obvious structural transformation under higher temperature or lower strain rate.The compressive strength of samples after deformation is slightly lower than that of as cast state,while it still retains the high strength characteristics of the cast state.With the increase of temperature or the decrease of strain rate,the crystallization temperature T_x decreases,the range of supercooled liquid zone narrows,and the enthalpy of heat release decreases.It will be in a crystallised state when the temperature is above 733 K and the strain rate is?1×10^-33 s^-1.Amorphous alloys are suitable for superplastic processing when they reach the state of Newtonian flow and do not crystallise.The appropriate processing parameters of(Cu₄₃Zr₄₈Al₉)₉₈Y₂ amorphous alloys is below the‘dividing line';when the temperature is above 733 K,the strain rate must be>1×10^-33 s^-1.The study of the non-isothermal and isothermal crystallization kinetics of(Cu₄₃Zr₄₈Al₉)_?100-x?Y_x?x=1,2,3?amorphous alloys shows that under non-isothermal conditions,the T_g,T_x and T_p move towards high temperature along with the increase of heating rate.The kinetic effect is obvious,and the dynamic effect of crystallization is more obvious than that of glass transition.The change of Y content has an effect on the crystallization kinetics of amorphous alloys.When x=2,the nucleation and growth process is easier than that of x=1.With the increase of Y content?x=3?,nucleation and growth of grains become difficult.With the increase of?,the local Avrami exponent n???of(Cu₄₃Zr₄₈Al₉)_?100-x?Y_x?x=1,2,3?amorphous alloys decreases with the increase of?.And in the early stage,the value of n is larger than 4,which means the fast crystallization rate and increasing crystal amount.And in the later stages,n is between 2 and 4,the crystallization rate is reduced,and the crystallization is slow.Under isothermal condition,the incubation period of(Cu₄₃Zr₄₈Al₉)_?100-x?Y_x?x=1,2,3?amorphous alloys were shortened with the increase of temperature.The change speed of volume fraction of three kinds of amorphous alloys in the crystallization process slow down with the decrease of holding temperature,and the activation energy will decrease with the increase of crystallization volume fraction.By calculating the Avrami index of n,the crystallization of three kinds of amorphous alloys are three-dimensional growth controlled by diffusion.Influenced by the content of Y,the crystallization of(Cu₄₃Zr₄₈Al₉)₉₉Y₁ and(Cu₄₃Zr₄₈Al₉)₉₇Y₃ are mainly accompanied by the growth of grains that increase with nucleation rate,and the crystallization of(Cu₄₃Zr₄₈Al₉)₉₈Y₂is mainly accompanied by the growth of grains that decrease with nucleation rate.