<Emphasis Type="Italic">In situ</Emphasis> synthesis of TiC reinforced Cu<Subscript>47</Subscript>Ti<Subscript>34</Subscript>Zr<Subscript>11</Subscript>Ni<Subscript>8</Subscript> bulk metallic glass composites

In situ synthesized TiC particles and β-Ti dendrites reinforced Cu47Ti34Zr11Ni8 bulk metallic glass (BMG) composite ingots were prepared by the suction casting method.The ingots with diameters from 1 up to 4mm were successfully obtained. It was shown that introducing TiC micro-sized particles into the amorphous matrix did not disturb the glass forming ability (GFA) of the matrix,while the yield strength and ductility could be well improved.The phase constitution, microstructure and elements distribution in the composites were studied by OM, XRD, SEM and EDS.It was shown that the in situ synthesized TiC particles acting as heterogeneous nucleation sites promoted the precipitation of β-Ti dendrites, resulting in the formation of the TiC particles and β-Ti dendrites co-reinforced BMG composites. The compressive tests were employed to probe the yield strength and ductility of BMG composites.     

Effect of Ag addition on the thermal stability and glass-forming ability of Zr<Subscript>35</Subscript>Ti<Subscript>30</Subscript>Cu<Subscript>7.5</Subscript>Be<Subscript>27.5</Subscript> bulk metallic glass

The thermal stability and glass forming ability (GFA) of Zr35-xTi30Cu7.5Be27.5Agx (x = 0-10) alloys were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and ultrasonic techniques. We found that the addition of 1 at.% Ag can considerably enhance the GFA as indicated by an increase in the critical glass dimension from 15 mm in the Zr35Ti30Cu7.5Be27.5 alloy to 20 mm in the Zr34Ti30Cu7.5Be27.5Ag1 alloy. However, with the addition of more Ag the supercooled liquid region (△Tx) and y parameter (defined as Tx/(Tg+Tl)) drastically decreased from 155 K and 0.436 to 76 K and 0.363, respectively, resulting in a decrease in the GFA. Additionally, the elastic constant (the ratio of shear modulus to bulk modulus or Poisson’s ratio) was also used as a gauge to evaluate the GFA in Zr35-xTi30Cu7.5Be27.5Agx alloys.     

Mechanical, deformation and fracture behaviors of bulk metallic glass composites reinforced by spherical B2 particles

Ti_(45)Cu_(40)Ni_7Zr_5Sn_(2.5)Si_(0.5) alloys were prepared under various cooling rate conditions during solidification.The alloys exhibited different volume fractions of B2 particles with 0～40 vol%in an amorphous matrix.Monolithic bulk metallic glass of 1 mm diameter showed no macroscopic plasticity and exhibited the typical vein patterns in a maximum shear stress plane on the fracture surface.However,a bulk metallic glass composite containing the B2 particles revealed obvious plasticity(～5.6%)with a remarkable work-hardening behavior that resulted from a stress-induced martensitic transformation of the B2 particles.Moreover,the composite displayed the complicated fracture morphologies containing of three types of fracture features.Through detailed investigations on the microstructural evolution,mechanical,deformation and fracture characteristics,the influence of B2 particle on overall behavior of the TiCu-based bulk metallic glass composites was elucidated.     

Correlation between the glass-forming ability and activation energy of crystallization for Zr75−x Ni25Al x metallic glasses

The thermal stability and the kinetics of glass transition and crystallization for Zr_75?x Ni₂₅Al _x (x = 8–15) metallic glasses were investigated using differential scanning calorimetry (DSC) under continuous heating conditions. The apparent activation energy of glass transition rises monotonously with the Al content increasing; the activation energy of crystallization increases with Al changing from 8at% to 15at%, and then decreases with Al further up to 24at%, which exhibits a good correlation to the thermal stability and the glass-forming ability (GFA). The Zr₆₀Ni₂₅Al₁₅ metallic glass with the largest supercooled liquid region and GFA possesses the highest activation energy of crystallization. The relation between the thermal stability, GFA and activation energy of crystallization was discussed in terms of the primary precipitated phases.     

Centimeter-sized Ti-based bulk metallic glass with high specific strength

Based on the quaternary Ti₄₁Zr₂₅Be₂₉Al₅ glassy alloy with a critical diameter of 7 mm reported not long ago, an obvious enhancement of glass-forming ability (GFA) has been realized in this alloy by the addition of Cu element. A series of (Ti₄₁Zr₂₅Be₂₉Al₅)_100?xCu_x (x=0, 2, 5, 7, 9, 11 at%) glassy alloys have been developed and some of them can be cast into one-centimeter diameter fully glassy rods by copper mold suction casting. It has been found that Cu addition could stabilize the liquid phase and suppress the crystallization, resulting in improvement of the GFA of the alloy. The addition of Cu also increases the compressive strength of the alloy and the (Ti₄₁Zr₂₅Be₂₉Al₅)₉₁Cu₉ glassy alloy possesses a specific strength (defined as yield strength/density) of 4.13×10⁵ Nm/kg, which is much higher than most other reported centimeter-sized bulk metallic glasses. The present result suggests that the newly developed (Ti₄₁Zr₂₅Be₂₉Al₅)₉₁Cu₉ glassy alloy is a good candidate for structural applications because of its good glass-forming ability and mechanical properties.     

Stable structure of Zr49Cu44Al7 metallic glass matrix composite with CuZr phase under high pressure up to 40.8 GPa

Ternary Zr₄₉Cu₄₄Al₇ metallic glass matrix composite rods with CuZr nano-phase, exhibiting an elastic strain of 1.6% and a high strength of 1.78 GPa, have been manufactured. The structural evaluation of the ternary metallic glass matrix composite under high pressure has been investigated using angle dispersive X-ray diffraction with a synchrotron radiation source. The investigation shows that the amorphous matrix structure is stable under pressures up to 40.8 GPa at room temperature. No pressure induced CuZr nano-phase disappearing or growing was detected. According to the Bridgeman equation of state, the bulk modulus B ₀ =115.2 GPa has been obtained.     

Rolling-induced microstructure change in Zr_（65）Al_（7.5）Ni_（10）Cu_（12.5）Ag_5 bulk metallic glass

The microstructures and free-volume evolutions of as-cast and pre-annealed Zr65Al7.5Ni10Cu12.5Ag5 bulk metallic glasses during rolling deformation have been investigated. No phase transformation is detected in the as-cast/rolled specimen. However,the structural stability of the glass against plastic deformation is worse after pre-annealing,indicated by nanocrystallization in preannealed/rolled specimens with large deformation degrees. Moreover,with increasing deformation degree,the free-volume content in a pre-annealed/rolled specimen increases at a lower average rate than that in an as-cast/rolled specimen.     

Dendritic and spherical crystal reinforced metallic glass matrix composites

Zr-based bulk metallic glass matrix composites (BMGMCs) with a composition of Zr_60.0Ti_14.7Nb_5.3Cu_5.6Ni_4.4Be_10.0 (at%) were fabricated by an innovative process, i.e., semisolid processing plus Bridgman solidification. Different morphologies, distributions, and volume fractions of the crystalline phases can be achieved by tailoring the withdrawal velocity. The largest fracture strain of Zr_60.0Ti_14.7Nb_5.3Cu_5.6Ni_4.4Be_10.0(at%) composites with the withdrawal velocity of 1.0 mm/s was found to be 16.7%. The mechanism of plasticity improvement is mainly attributed to the interpenetrated structure of the crystalline phase, which greatly confines the rapid propagation of shear bands.     

Mechanism of Ag and Al on improving the glass forming ability of CuZr-based alloys

By a mean field theoretical computation, the equilibrium distributions of additional Ag and Al in the crystalline phase of CuZr-based alloys were determined to occupy the two sublattices of the B2 structure randomly. With the molecular dynamics technique, the effects of Ag and Al on the enthalpy difference (ΔH) between the supercooled melt and the crystalline phase were evaluated. The improved glass forming ability of Cu₄₅Zr₄₅Al₁₀and Cu₄₅Zr₄₅Ag₁₀ can be attributed to their remarkably smaller ΔH than that of CuZr. The calculated diffusion coefficients are more sensitive to the atomic weight of the component atoms than to their interaction strength. As the component atom with the largest mass, the additional Ag increases the viscosity of the supercooled melt significantly and the experimentally stronger glass formation ability of Cu₄₅Zr₄₅Ag₁₀ than Cu₄₅Zr₄₅Al₁₀ can be well understood.     

Strain rate response of a Zr-based composite fabricated by Bridgman solidification

Zr_58.5Ti_14.3Nb_5.2Cu_6.1Ni_4.9Be_11.0 bulk metallic glass matrix composites, containing β-Zr dendrites, were fabricated by Bridgman solidification at the withdrawal velocity of 1.0 mm/s through a temperature gradient of ～45 K/mm. Subjected to the increasing compressive strain rates, the monotonic increasing and decreasing were obtained for the maximum strength and the fracture strain, respectively. The results show that high strain rate may induce the insufficient time for the interaction between shear bands and the crystalline phase, and early fracture occurs as a result. The fractographs are consistent with the mechanical properties, and the failure mode of the present Zr-based composites is in agreement with the frame of the ellipse criterion.     

Bulk metallic glass rings prepared by a modified water quenching method

Bulk metallic glass rings have the potential applications as annular gasket and active solder in special fields. The bulk metallic glass ring of Zr_1.2Ti_13.8Cu_12.5Ni_10.0Be_22.5 with the outer diameter, the inner diameter, and the thickness of 38, 36, and 5 mm, respectively, was prepared by using a special shaped quartz tube water quenching method. The mechanical properties along the whole cross section were investigated by a nanoindentation method, and no evident variation of the Young's modulus and hardness was found, further indicating the single amorphous structure. Amorphous ring and tube-shape parts with different dimensions can be produced by this method.     

Formation and mechanical properties of Zr-based bulk metallic glass composites with high oxygen levels

Zr-based bulk metallic glass(BMG) composites with in situ formed Y 2 O 3 particle reinforcements were synthesized by proper additions of Y to ultrahigh-oxygen-containing glass-forming alloy precursors.Microstructures,thermal stabilities,and mechanical properties of the composites were investigated.Glass formation was greatly enhanced by Y additions in the alloys and the resultant particles were homogenously distributed in the glassy matrix,allowing for the fabrication of oxide dispersion strengthened BMG composites.The compressive strength and hardness increased by 10% and 20%,respectively,with the introduction of Y 2 O 3 particles.These results are significant for the design and production of Zr-based BMGs and BMG composites with improved properties using commercial high-oxygen content raw materials under industrial conditions.     

Revisiting Al-Ni-Zr bulk metallic glasses using the ＇cluster-resonance＇ model

Six series of alloys,namely,Ni3Zr6Alx,Ni3Zr7Alx,Ni4Zr9Alx,Ni3Zr8Alx,Ni3Zr9Alx and Ni3Zr10Alx (x=1,1.5,2,3) were designed in this work and the bulk metallic glass (BMG) formation of these compositions was investigated by copper mold suction casting. A centimeter-scale BMG sample was obtained for the Ni4Zr9Al2 (Al13.3Ni26.7Zr60 in atomic percent) composition. The thermal glass parameters for this BMG were determined to be ΔTx = 68 K,Trg = 0.579,and γm = 0.689. Using the ’cluster-resonance’ model for glass formation an optimal BMG composition was determined using the cluster formula [Ni3Zr9](Al2Ni1).     

Formation and biocorrosion behavior of Zr-Al-Co-Nb bulk metallic glasses

Ni-and Cu-free Zr-Al-Co-Nb glassy alloys with different Nb and Co contents were synthesized by melt spinning and copper mold casting.The effects of Nb addition to partially replace Co in the Zr55Al20Co25 glassy alloy on the glass-forming ability,thermal properties,in-vitro biocorrosion behavior and surface wettability of the metallic glasses were investigated.Although addition of Nb up to 5 at.% slightly decreased the supercooled liquid region and the glass-forming ability(GFA),the alloys could be casted in a bulk glassy rod form with diameters up to 3mm.The Zr-Al-Co-Nb glassy alloys were spontaneously passivated with low passive current densities in phosphate buffered saline and Hanks’ solution.Substitution of "toxic" Co by Nb is effective in improved the corrosion resistance of the Zr-Al-Co glassy alloy.Water contact angle measurements showed that Nb addition increased the hydrophilicity of the glassy alloys,which may enhance cell adhesion of the alloys in biomedical applications.     

Fabrication of bulk glassy Zr41Ti14Ni8Cu12.5Be22.5Fe2 alloy by water quenching

A glassy Zr₄₁Ti₁₄Ni₈Cu_12.5Be_22.5Fe₂ rod with a diameter of 9 mm was successfully produced by water quenching. The effects of iron addition on thermal stability and hardness of Zr₄₁Ti₁₄Ni₈Cu_12.5Be_22.5Fe₂ bulk amorphous alloy were investigated by XR D, DSC and microhardness test. It is found that the full annealing would enhance the strength of the alloy significantly. The cause of the increase in hardness was analyzed and the formation mechanisms of the bulk amorphous alloy are discussed.     

Effects of gravity field on glass forming ability in ZrTiCuNiBe alloy

The solidification and glass forming ability of Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 bulk glassy forming alloy is investigated by Bridgman unidirectional solidification at different growth velocities under different gravity field orientations. Large differences in glass formation, undercooling and crystallization morphology on different solidification conditions have been found and discussed from the point of view of gravity induced convection. The results are useful for understanding the nucleation and growth in the melt and glass formation mechanism in the alloy.     

块状金属玻璃Zr55Cu30Al10Ni5的微压痕尺寸效应

基于Drucker-Prager屈服准则,建立了适用于描述压敏材料的低阶应变梯度塑性(CMSG)理论. 通过ABAQUS自定义材料子程序(UMAT),构造了CMSG理论本构计算的有限元格式,并对块状金属玻璃Zr₅₅Cu₃₀Al₁₀Ni₅的圆锥压痕实验响应进行了数值模拟分析. 计算结果与实验数据相吻合,表明该理论可以很好地描述金属玻璃的弹塑性行为. 在此基础上,研究了不同压深下的载荷位移曲线和硬度,计算结果显示该材料的硬度随着压痕深度的增大而减小,表明基于Drucker-Prager屈服准则的CMSG理论可以预测金属玻璃Zr₅₅Cu₃₀Al₁₀Ni₅在微米尺度下表现出来的尺寸效应现象. 此外,通过分析不同摩擦因数下材料的载荷位移曲线,表明摩擦力对该材料微压痕响应的影响可以忽略不计.     

Atomic packing and short-to-medium range order evolution of Zr-Pd metallic glass

A larger-scale Zr₇₀Pd₃₀ alloy system has been simulated using molecular dynamics (MD) to investigate structure evolution in Zr₇₀Pd₃₀ metallic glass. The simulated pair distribution function of Zr₇₀Pd₃₀ metallic glass agrees well with the experimental results. Voronoi polyhedron analysis indicates that the icosahedra are not randomly distributed in space, but form characteristic intercrossed icosahedral clusters with medium-range order. Intercrossed icosahedral clusters are the dominant local configurations in Zr₇₀Pd₃₀ metallic glass and probably cause the quasicrystalline phase discovered in Zr₇₀Pd₃₀ metallic glass.     

Transitions of amorphouscrystalline-amorphous in bulk metallic glass under HP and HT

In-situ SR-XRD measurements revealed that the crystallization process in Zr₄₁.2Ti₁₃.8Cu_12.5Ni₁₀Be_22.5 bulk metallic glass is significantly different from that in traditional glasses. Subsequent heating at 10 GPa converts the sample from amorphous phase into the metastable fcc phase and then leads to the fcc phase back to the amorphous phase, indicating that there exists ‘reversible’ phase transition phenomena in the material under high pressure and high temperature.     

Eutectic reaction and cored dendritic morphology in yttrium doped Zr-based amorphous alloys

The microalloying effect of yttrium on the crystallization behaviors of (Zr_0.525Al_0.10Ti_0.05Cu_0.179Ni_0.146)_100-x Y_x, and (Zr_0.55Al_0.15-Ni_0.10Cu_0.20)_100-x Y_x (x=0, 0.4, and 1, thus the two alloy systems were denoted as Zr52.5, Zr52.5Y0.4, Zr52.5Y1, and Zr55, Zr55Y0.4, Zr55Y1, respectively) was studied. Transmission electron microscopy (TEM) results suggested that the crystalline phases were different in the two Zr-based alloys and with different yttrium contents. ZrNi-phase and Al₃Zr₅ phase precipitations can be well explained by the mechanisms of nucleation and growth. Al₃Zr₅ phase is mainly formed by a peritectic-like reaction, while ZrNi-phase by a eutectic reaction. The contents of elements Y, Al, and Ti may dominate the reaction types. The orientation relationship between Y₂O₃ particles and Al₃Zr₅ phase is also discussed.