Study On Microstructure And Mechanical Properties Of Five Element Zr Based Amorphous Alloys

Zr-based amorphous alloys can easily obtain a larger size because of its wider supercooled liquid region and higher glass formation ability.However,the room temperature tensile plasticity of Zr-based amorphous alloys is almost zero,which severely prevent their further application as a structural material.In this thesis,five-element amorphous alloy Zr₅₀Al₅Ni₁₅Cu₁₅Co₁₅ were prepared as the basic research components,then tailored the ratio of Co/Ni and Co/Cu in Zr₅₀Al₅Ni₁₅Cu₁₅Co₁₅alloys to form the alloy system.The copper roll spinning method and vacuum annealing were used to manufacture the amorphous alloy and nanocrystalline alloys.By X-ray diffraction（XRD）,differential scanning calorimetry（DSC）,scanning electron microscope（SEM）and transmission electron microscope（TEM）,the microstructure,supercooled liquid region,the ability of amorphous formation and tensile mechanical properties of the materials were analyzed.The effects of alloy composition,annealing temperature,time and ribbon thickness on the microstructure and tensile mechanical properties of the alloy were revealed,the main conclusions are as follows:（1）All 21～74μm ribbons are amorphous structure with typical room temperature brittleness.The Cu Zr and Co Zr phases precipitated on the amorphous substrate after vacuum annealing.Under the same annealing temperature and time,the thinner the ribbons are,the greater the tensile strength and plasticity are.The tensile strength and plasticity decrease with the increasing annealing temperature.The tensile strength decreases first and then increases with the rising thickness,while the tensile plasticity increases first and then decreases.When the ribbon,annealed at 513°C for 1800 s,is 21μm in thickness,the alloy exhibit good comprehensive mechanical properties.Its tensile strength is 1104.76 MPa,and the tensile plasticity at room temperature reach 8.4%.（2）The structure of the samples does not change after partial substitution of Ni element by Co,and all the samples show amorphous characteristics,and the center position of diffuse peak does not shift significantly.After annealing,plastic Cu Zr phase and Co Zr phase precipitate on the amorphous matrix,forming the composite structure of amorphous and nanocrystalline.With the decrease of Ni content,the transition temperatures of glassy alloy do not change,but the crystallization temperatures shift to a higher region,which leads to the increase of the width of the supercooled liquid region and the decrease of the tensile strength at room temperature.The tensile strength of the samples increases first and then decreases with the gradual increase of ribbon thickness,and the overall tensile plasticity shows an increasing trend.（3）The structure of the samples are amorphous,drawing a typical amorphous diffuse scattering peak.After annealing treatment,Cu Zr and Co Zr nanocrystals precipitated in Zr₅₀Al₅Ni₁₅Cu_15-xCo_15+x（x=2,4,6 at%）ribbons,forming an amorphous and nanocrystalline composite structure.With the decrease of Cu content,the glass formation temperature T_g and the initial crystallization temperature T_x move to a higher temperature,and the width of the supercooled liquid region is almost the same,while the tensile strength of the alloy decreases first and then increases.After annealing,the tensile strength and tensile plasticity of the alloy with different Cu content decrease first and then increase with the gradual increasing thickness.