On The Microstructure And Properties Of Zr-Co Based Alloys Prepared By Rapid Solidification

With the rapid development of science and technology,the properties of materials,such as strength,hardness,plasticity and toughness,are being put forward to higher requirements in many fields.Most of intermetallics not only possess a lot of excellent performances,such as high hardness,high strength and corrosion resistance,but also can be prepared into single crystal,polycrystalline or amorphous bulk materials.Therefore,there is great potential in preparing new high performance materials on the base of intermetallic compounds.However,the uses of intermetallics are being limited because of the poor plasticity and the difficult of forming.It is needed to carry out the related research.In this work,Zr-Co based alloys became the research subject because of the wide application prospect in the fields of biomaterials and nuclear reactor structural materials.Taking high purity Zr,Co,Al and Fe as raw materials,Zr-Co-(Al)alloys and Zr-Co-Al-Fe alloys were prepared by using rapid solidification technology.The effects of components on the microstructure and properties of Zr-Co based alloys,the deformation behaviors and strengthening-toughening mechanisms of Zr-Co-(Al)alloys,the thermostability of amorphous Zr-Co-Al-Fe alloys were investigated systematically using optical microscopy,X-ray diffractometer,scanning electron microscopy,transmission electron microscopy,synchrotron radiation high-energy X-ray diffraction and superconducting quantum interference device.The results can be drawn as folowing:The effects of components on the microstructure and properties of ZrCo based alloys are distinct.The microstructure of Zr50-x/2Co50-x/2Alx(x=0～10 at.%)alloys changed from B2 single phase to multi-phases of B2,Zr5Co7Al3 intermetallics and amorphous with the increasing of Al content,resulting in the increasing hardness and poor plasticity and ductility.Zr49Co49Al2 alloy possesses excellent comprehensive mechanical properties,and the ultimate compressive strength,hardness and compressive plastic strain were 2.26GPa,406 HV and over 50%respectively.The GFA of Zr56Co28-xAl16Fex(x=1,2 at.%)alloys is excellent.Zr56Co27A116Fe and Zr56Co26Al16Fe2 BMGs also possess good comprehensive mechanical properties,and the yield strength and UCS of these alloys were over 1.90 GPa and 2.1 GPa respectively,and the plastic strain exceeded 11%.The pronounced significant work-hardening behavior of Zr50Co50and Zr49Co49Al2 alloys occurred in the process of compression,which attributed the excellent room temperature plasticity and strength.With increasing the content of Al,the room temperature plasticity and strength of Zr50-x/2Co50-x/2Alx alloys decrease associated with the decreasing of work-hardening behavior of these alloys.At liquid Nitrogen temperature,Zr50-x/2Co50-x/2Alx alloys also possess good comprehensive mechanical properties,and the strength and plasticity increased compared to room temperature.The UCS of Zr49Co49Al2 alloy increased by 1 GPa,and the plasticity of Zr45Co45Al10 alloy increased to 20.89%,which is about 4 times of room temperature value.From the research above,we can see that the strengthening mechanisms of Zr50-x/2Co50-x/2Alx alloys at room temperature are combination of solution strengthening of Al element,precipitation strengthening of Zr5CO7Al3 intermetallics and amorphous,work-hardening and martensite strengthening.With increasing the content of Al,the effects of solution strengthening and precipitation strengthening increased,but the effects of martensite strengthening decreased.The population of slip system is unchanged when Zr50-x/2Co50-x/2Alx alloys were compressed at room temperature,and the remarkable enhancement of ductility is due to the transformation-induced plasticity associated with deformation-induced B2 to B33 martensite.The thermostability of amorphous Zr-Co-Al-Fe alloys has been done and it has been found out that the glass transition and crystallization behavior of Zr56Co28-xAl16Fex(x=1,2)BMGs are related with the heating rate,and Tg、Tx、Tp1、Tp2 and △T shifted to high temperature with increasing heating rate.Thus the crystallization behavior shows obvious dynamic effect.The minor substitution of Fe to Co element can improve the GFA.However,it also decreased the apparent activation energy,and promoted the crystallization process,and decreased the resistance to crystallization and thermostability.