Studies Of Preparation And Thermal Stability Of High-plasticity Zr-based Bulk Metallic Glasses Designed By Quasicrystals

Bulk metallic glasses（BMGs）exhibit enticing prospects for applications in fields such as electronics,mechanics,chemistry,aerospace,and aviation due to their unique structure and excellent physicochemical properties.However,their application is significantly limited by the small critical size and poor room temperature plasticity.Furthermore,BMGs are prone to aging and crystallization during service due to changes in the internal atomic structure,leading to a severe deterioration in the structure and properties of the BMGs.The thermal stability of BMGs is a crucial issue that has garnered significant attention,impacting their application.In response to these challenges,there has been a special focus on the research related to the preparation of BMGs with high glass-forming ability,enhanced plasticity,and improved thermal stability.Previous studies have revealed that the icosahedral short-range order in the molten state is conducive to inhibiting crystallization and promoting the formation of an amorphous structure.However,it can also lead to the unevenness of the local structure of the BMG,thereby improving its plasticity.This study focuses on the Zr₄₀Ti₄₀Ni₂₀ icosahedral quasicrystal as the master alloy,employing a microalloying approach.By optimizing the addition of Be and Nb elements as alloying elements,the glass forming ability,mechanical properties,and thermal stability of the microalloyed(Zr₄₀Ti₄₀Ni₂₀)_100-xBe_x and((Zr₄₀Ti₄₀Ni₂₀)_100-xBe_x)_100-yNb_y systems were investigated using techniques such as X-ray diffraction,universal testing machine,scanning electron microscopy,and differential scanning calorimetry.Microstructure analyses of(Zr₄₀Ti₄₀Ni₂₀)_100-xBe_x system reveal that the addition of Be initially increases the glass-forming ability,reaching a maximum non-crystalline size of over 20mm when Be content reaches 28 at.%.Subsequently,two compositions with good glass-forming ability,(Zr₄₀Ti₄₀Ni₂₀)₇₆Be₂₄and(Zr₄₀Ti₄₀Ni₂₀)₇₂Be₂₈,were selected,and Nb element was added.Results show that the glass-forming ability of(Zr₄₀Ti₄₀Ni₂₀)₇₆Be₂₄initially increases and then decreases with Nb addition,and the critical size increases from10 mm to 11.25 mm at 6 at.%Nb content.On the other hand,the glass-forming ability of(Zr₄₀Ti₄₀Ni₂₀)₇₂Be₂₈ slightly decreases with the initial addition of Nb,but when Nb content reaches 12 at.%,the maximum non-crystalline size reaches 20 mm again.The elements Be and Nb change the topology and thermodynamic properties of the system due to their size difference and binding interaction difference with the main elements,thus improving the formation of amorphous alloys.Uniaxial compression experiments are conducted on(Zr₄₀Ti₄₀Ni₂₀)_100-xBe_x and((Zr₄₀Ti₄₀Ni₂₀)_100-xBe_x)_100-yNb_y systems,showing that the addition of Be improves the fracture strength and plastic deformation of(Zr₄₀Ti₄₀Ni₂₀)_100-xBe_x system.The alloy exhibits optimal comprehensive performance with a fracture strength of 2154 MPa and plasticity of14.6%when Be content is 24 at.%.Further addition of Nb to(Zr₄₀Ti₄₀Ni₂₀)₇₆Be₂₄ and(Zr₄₀Ti₄₀Ni₂₀)₇₂Be₂₈ leads to further enhancement in strength and plasticity,with((Zr₄₀Ti₄₀Ni₂₀)₇₂Be₂₈)₉₇Nb₃ amorphous alloy showing the best comprehensive mechanical properties,with strength and plasticity reaching 2846.0 MPa and 29.7%,respectively.The amorphous alloys designed based on icosahedral quasicrystals were found to precipitate crystalline phases with icosahedral quasicrystalline structures after a period of annealing,which indicates that(Zr₄₀Ti₄₀Ni₂₀)_100-xBe_x amorphous alloys designed based on quasicrystals may have a large number of short-range ordered clusters（e.g.,strong icosahedral short-range ordered structures and twisted icosahedral ordered structures）,and that a series of unstable weak polyhedral atomic clusters are possible.A series of unstable weak polyhedral atomic clusters,these heterogeneous structures provide nucleation points for the shear transition zone and prevent the extension of the shear band,which is the main reason for the high plasticity of amorphous alloys.After continuing to add the Nb element with positive mixing heat,phase separation may occur resulting in locally different chemical compositions and different atomic packing density structures,forming a non-homogeneous organization,further improving the plasticity of amorphous alloys.Thermal stability tests are conducted on(Zr₄₀Ti₄₀Ni₂₀)_100-xBe_x and((Zr₄₀Ti₄₀Ni₂₀)_100-xBe_x)_100-yNb_y systems,indicating that(Zr₄₀Ti₄₀Ni₂₀)₇₆Be₂₄ alloy has the highest crystallization onset apparent activation energy and peak apparent activation energy when the Be content is 24 at.%,reaching 266.74 k J·mol^-1 and 370.46 k J·mol^-1,respectively.At this point,the alloy exhibits the highest thermal stability with the largest energy barrier for crystallization and growth.After adding Nb,the crystallization onset apparent activation energy of((Zr₄₀Ti₄₀Ni₂₀)₇₆Be₂₄)_100-yNb_y metallic glasses increases,while the peak apparent activation energy decreases.As for((Zr₄₀Ti₄₀Ni₂₀)₇₂Be₂₈)_100-yNb_y amorphous alloy,the crystallization onset apparent activation energy initially increases and then decreases with the increase of Nb content,and the best thermal stability is achieved when Nb content is 3at.%,with crystallization onset apparent activation energy and peak apparent activation energy reaching 241.18 and 344.89 k J·mol^-1,respectively.The first crystallization peak of(Zr₄₀Ti₄₀Ni₂₀)_100-xBe_x and((Zr₄₀Ti₄₀Ni₂₀)_100-xBe_x)_100-yNb_y amorphous alloys are both controlled by three-dimensional growth governed by diffusion,but the nucleation rate varies.The addition of Be does not significantly change the nucleation rate,while the addition of Nb reduces the nucleation rate of((Zr₄₀Ti₄₀Ni₂₀)_100-xBe_x)_100-yNb_y metallic glasses.