Creep Behaviors Of TiZrNiCuBe Bulk Metallic Glass

The bulk metallic glass has excellent mechanical properties as a new material.In this thesis,Ti₄₀Zr₂₅Ni₃Cu₁₂Be₂₀ bulk amorphous alloy?BAA?samples of as-cast,annealed and crystallines states,were selected as model materials.The tensile creep behaviors and their deformation mechanism have been studied.The nanoindentation creep tests of the BAA samples with different structural states have been performed to explore the nano-scale creep mechanism.The microstructure of the deformation and clamping regions of the Ti₄₀Zr₂₅Ni₃Cu₁₂Be₂₀ BAA were examined by transmission electron microscopy?TEM?after tensile creep tests.The ordered degree of BAA samples increases with increasing the applied creep stress and creep temperature.The degree of crystallization in the deformation zone is increasing and the nanocrystalline is precipitated in the deformation zone.The order of the microstructure of the annealed amorphous alloy was observed.The order of the microstructure was increased with the increase of the annealing temperature,and the nanocrystals with the size of 5 10 nm were localized.The samples of the crystallin e amorphous alloy were observed and the size of the precipitated nanocrystals was increased with the increase of the degree of crystallization.The tensile creep behavior of amorphous alloys was discussed by X-ray diffraction?XRD?curves.The results show that the main fracture mode of Ti₄₀Zr₂₅Ni₃Cu₁₂Be₂₀ amorphous alloy is brittle fracture.The creep process is mainly affected by local nonuniform shear stress.The effect of the applied load on the ordered degree of amorphous alloy is obvious.The morphology of the fracture surface was analyzed by scanning electron microscopy?SEM?,and the fracture surface showed a distinct amorphous brittle topography?river pattern?.With the increase of the stress and temperature,the number and density of the faulted r iver pattern also occurred Variety.When the conditions are 670 K,200MPa,the fracture occurs "droplet" situation.The fracture zone and the clamping zone were analyzed by differential scanning calorimetry?DSC?,and the degree of crystallization of the fracture zone and the clamping zone under different stress and temperature conditions was determined.The results show that the degree of crystallization of the material increases with the increase of external stress and temperature.When the external conditions are 670 K and 200 MPa,the degree of crystallization is the most serious.The nano-indentation creep behaviors and their mechanism of the annealed BAA samples were studied by nanoindenter,XRD,DSC and TEM.The ordered degree of the Ti₄₀Zr₂₅Ni₃Cu₁₂Be₂₀ BAA increases and the creep resistance gradually enhances with the increase in the annealing temperature.The as-cast BAA exhibits the worst creep resistance,whereas the BAA sample annealed at 320 ° C for one hour shows the best creep resistance.The XRD results show that the sample maintains its amorphous state after annealing process.TEM observations indicate that the sample does not crystallize with the increase in the annealing temperature,but the ordered degree increases.Additionally,a higher appl ied creep stress causes the worse creep resistance.The creep depth of the BAA samples,and the steady-state creep rate during the 300-second maximum load holding process increases with increasing the applied stressThe nanoindentation creep behavior of the crystalline amorphous alloy was analyzed by means of nanoindentation curve,XRD curve,DSC curve and TEM.The XRD curves show that the crystallization of the samples occurs after different degree of crystallization,and the DSC curves have their precise crystallization fraction.TEM and electron diffraction results show that the material appears a large number of nanocrystals after crystallization.The results of the nanoindentation creep curve show that the creep resistance of the material decreases with the increase of crystallinity under the same load condition.When the degree of crystallization is the same,the sample has a strong dependence on the external load.With the increase of the external load,the depth of the pressing head is increased,the creep displacement in the creep steady state stage increases and the steady creep rate increases.The nanoindentation creep behaviors and their mechanism of the crystallized BAA samples were studied by nanoindenter,XRD,DSC and TEM.XRD results revealed that the sample crystallized after heat treatment.TEM observations suggested that numerous nano-scale crystals appeared in the samples.For the case of the same maximum load,the increase in the crystallization volume fraction of the crystallized samples promots the creep resistance.Additionally,a higher maximum load results in a larger depth and a higher steady-state creep rate during load holding process.