The Deformation Behavior And Strengthening And Toughening Mechanism Of Zr-Co(-Al) Alloy

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 and high strength.It has great application prospect in the field of preparing new high strength materials.However,the ductility of most intermetallic compounds is poor at room temperature.It is necessary to improve the toughness and strength of the intermetallic compounds to improve comprehensive properties.In this paper,Zr-Co based alloys with intrinsic plasticity became the research subject.Taking high purity Zr,Co and Al as raw materials,Zr-Co（-Al）alloys were prepared by using suction casting technology for water-cooled copper mould.The effects of components and preparation process on the microstructure and properties of Zr-Co（-Al）alloys,the deformation behaviors and strengthening-toughening mechanisms of Zr-Co（-Al）alloys were investigated systematically using metallographic microscope,microhardness meter,X ray diffractometer,electronic universal testing machine,scanning electron microscope and transmission electron microscope.At the same time,the phase stability,elastic properties and electronic structure of B2 and B33 phase ZrCo were calculated by first principles.The results can be drawn as folowing:The microstructures and properties of Zr-Co（-Al）alloys were significantly affected by the components and preparation process.The microstructure of Zr_50-x/2Co_50-x/2Al_x（x=0,4,5,6,7,8）alloys changed from B2 single phase to multi-phases of B2 and Zr₅Co₇Al₃ intermetallics with the increasing of Al content,resulting in grain refinement,increasing strength and hardness,and decreasing plasticity and ductility.The ultimate compressive strength ofφ2 mm andφ3 mm Zr_46.5Co_46.5Al₇ alloy bars are about 1820 MPa and 1787 MPa respectively,and the ultimate failure strain are more than 25%.Therefore,Zr_46.5Co_46.5Al₇ alloy bars have excellent comprehensive compressive mechanical properties.The larger cooling rate could increase the solid solubility of Al element,decrease the content of the second phase at grain boundary,and reduces the yield strength of the alloy due to the micro-defects.Zr₅₀Co₅₀ alloys have a stable work hardening index during compression,which attributed the excellent compressive plasticity and strength.The work hardening index of Zr_50-x/2Co_50-x/2Al_x（x=4,5,6,7）alloys are higher inⅠregion and decreased inⅡregion,but they can still show a certain degree of uniform plastic deformation.The strengthening and toughening mechanisms of Zr_50-x/2Co_50-x/2Al_x（x=0,4,5,6,7,8）alloys are combination of fine grain strengthening,solution strengthening,second phase strengthening,dislocation strengthening,microcrack toughening,work hardening,deformation induced martensite transformation and transformation induced plasticity.The formation energy indicates that B33 ZrCo is more stable than B2 ZrCo under different pressure.The elastic properties of B2 and B33 ZrCo increase with increasing pressure.The calculated results of the universal anisotropy index and Zener anisotropy index show that B2 and B33 phases are anisotropic.Furthermore,the electronic structures under high pressure show that the electronic densities of states（DOS）at the Fermi level decrease and the charge distribution changes,resulting in a decline in the structural stability for B2 and B33 ZrCo compounds.