Studying On The Microstructure And Properties Of TiZrCuBe System Amorphous Composites By Semi-solid Isothermal Treatment

Amorphous composites have the advantages of high elastic limit,excellent corrosion resistance,high magnetic permeability,and can be used for semiconductor,but the shortcomings such as low plasticity,brittleness and brittle fracture are easy to occur.So this article adopts a semi-solid isothermal heat treatment(SSIT)and composition design to improve the plasticity of amorphous composites,and the main conclusions were as follows:This paper takes Ti-based amorphous composite Ti48Zr27Cu6Be14M5 as the research object,and prepares Ti48Zr27Cu6Be14Ta5,Ti48Zr27Cu6Be14Nb5,Ti48Zr27Cu6Be1414V5,Ti48Zr27Cu6Be14V5 and Ti48Zr27Cu6Be14Co5 by water-cooled copper mold method.Carry out semi-solid isothermal heat treatment,and Ta5,Nb5,V5 and Co5 are used as the codes of the four sets of samples,respectively.The semi-solid process is 900?,10 min.It is found that among the four groups of as-cast samples,Nb5 has the best plasticity,6.3%,and its yield strength is 1470.1MPa,only second to the worst plasticity of Co5 sample.After semi-solid treatment,Nb5 has a plasticity of 10.2%,only second to V5 sample,and its yield strength is not as good as that of V5,Co5 and Ta5 samples,while Co5 and Ta5 have poor plasticity,only 4.2%and 4.5%.Combining the comprehensive properties of as-cast and semi-solid samples,Nb5 is the best.The reason is that Co is an element that promotes the formation of amorphous,so that the solid phase rate of Co5 material is low,which mainly reflects the amorphous performance,high strength and poor plasticity.Ta promotes crystal formation,so the solid phase ratio of the Ta5 is high,but its plasticity is still poor.The main reason is that ?-Ti crystals containing Ta elements transform to a-Ti during the strain process,and a-Ti is difficult to slip,so the plasticity of Ta5 is poor.Taking Nb5 as the research object,setting 6 groups of temperature(680,750,850,900,950 and 1000?)and 4 groups of time(5,10,20 and 40 min)for semi-solid isothermal treatment,the results show:with the SSIT time is extended and the temperature rises,the crystal grains have a tendency to grow.At the same time,as the temperature of SSIT increases,the plasticity first increases and then decreases.When the temperature is 950? and the time is 10min,the best plastic value is 18.8%,which is an increase of 198.4%relative to the as-cast sample.Through the analysis of the microstructure,it is concluded that the evolution mechanism of the microstructure is:dendrite growth?dendrite arms connected,grid-like crystals?necking at the connection,partial fracture?formation of striped crystals and granular crystals?striped crystals and granular Crystal spheroidization?large crystals merging small crystals?crystals grow up.By adjusting the content of Nb element,explore its effect on the mechanical properties and microstructure of(Ti50.3Zr28.5Cu6.4Be14.8)100-xNbx,(x=0,1,3,5,7and 9),and the semi-solid process is 900?,10 min.It can be seen from the test results that as the Nb element content increases,the yield strength of the as-cast and semi-solid samples gradually decreases,and the plasticity gradually increases.The plasticity of as-cast Nb9 is 11.8%,and the plasticity of semi-solid Nb9 is 22.9%,an increase of 94%.The solid phase ratio of the as-cast and semi-solid samples increases with the increase of the Nb element content and the solid phase ratio of Nb9 is 42.62%,while the equivalent diameter of the semi-solid sample gradually decreases.Observing the morphology of the shear bands of the fractured samples,it is concluded that the number of shear bands in the semi-solid samples is large,dense,and densely distributed.The main reason is that the expansion of shear bands is blocked by the crystals,which lead to a series of evolution.The evolution characteristics,such as the proliferation,multiplexing,bifurcation,bending,and expansion direction deviation of the shear bands,promote the improvement of plasticity.In addition,a comparative analysis of the shear bands in different regions show that as the distance from the fracture surface increasing,the number of shear bands gradually decreases,the distribution density gradually decreases,and the evolution behaviors of the shear bands gradually weaken until disappear,revealing the non-uniform deformation and mechanism of uneven stress distribution.For the as-cast samples,the number of shear bands in the as-cast samples is small,the distribution is sparse,extending along a straight line,and the extension length is large.The research has concluded that the mechanism leading to the poor plasticity of the as-cast specimen is:the crystal cannot hinder the expansion of the shear band,and the shear band extends in a straight line by passing through the crystals or bypassing the edge of the crystals.The extension length is large,even unlimited expansion,and finally leads to the material low plasticity brittle fracture occurs.Semi-solid isothermal treatment can greatly improve the plasticity of materials.The main mechanism is that large-size crystals are obtained after processing.The crystals have the dual effect of being easier to produce shear bands and can well hinder the expansion of shear bands,which greatly improves the plasticity.