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.     

Influence of pulsing current on the glass transition and crystallizing kinetics of a Zr base bulk amorphous alloy

Based on the thermal analysis, the influence of pulsing current on the glass transition and crystallizing kinetics of Zr41.3Ti14.2CU12.8Ni10.3Be21.4 bulk amorphous alloy has been studied. The obtained results show that after the Zr41.3Ti14.2CU12.8Ni10.3Be21.4 bulk amorphous alloy was pretreated by high-density pulsing current at low temperature, its glass transition temperature Tg, the initial crystallizing temperature Tx and the corresponding exothermic peak of crystallization Tpi were reduced. But the temperature range of supercooled liquid △T=Tx-Tg is almost the same. The calculated results with Kissinger equation show that the activation energy of glass transition of the alloy pretreated is reduced significantly, while the activation energy of crystallization is basically unchanged. The influence of pulsing current on the glass transition and crystallization of theZr41.3Ti14.2CU12.8Ni10.3Be21.4 bulk amorphous alloy is believed to be related with the structure relaxation of the glass caused by the current.     

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.     

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.     

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.     

A Ti–Zr–Cu–Ni–Co–Fe–Al–Sn amorphous filler metal for improving the strength of Ti–6Al–4V alloy brazing joint

Ti_(50)Zr_(27)Cu_8Ni_4Co_3Fe_2Al_3Sn_3(at%) amorphous filler metal with low Cu and Ni contents in a melt-spun ribbon form was developed for improving mechanical properties of Ti–6Al–4V alloy brazing joint through decreasing brittle intermetallics in the braze zone. Investigation on the crystallization behavior of the multicomponent Ti–Zr–Cu–Ni–Co–Fe–Al–Sn amorphous alloy indicates the high stability of the supercooled liquid against crystallization that favors the formation of amorphous structure. The Ti–6Al–4V joint brazed with this Ti-based amorphous filler metal with low total content of Cu and Ni at 1203K for 900s mainly consists of α-Ti, β-Ti,minor Ti–Zr-rich phase and only a small amount of Ti_3Cu intermetallics, leading to the high shear strength of the joint of about 460 MPa. Multicomponent composition design of amorphous alloys is an effective way of tailoring filler metals for improving the joint strength.     

Preparation of Al<Subscript>72</Subscript>Ni<Subscript>8</Subscript>Ti<Subscript>8</Subscript>Zr<Subscript>6</Subscript>Nb<Subscript>3</Subscript>Y<Subscript>3</Subscript> amorphous powders and bulk materials

Amorphous Al₇₂Ni₈Ti₈Zr₆Nb₃Y₃ powders were successfully fabricated by mechanical alloying. The microstructure, glass-forming ability, and crystallization behavior of amorphous Al₇₂Ni₈Ti₈Zr₆Nb₃Y₃ powders were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). The isothermal crystallization kinetics was analyzed by the Johnson–Mehl–Avrami equation. In the results, the supercooled liquid region of the amorphous alloy is as high as 81 K, as determined by non-isothermal DSC curves. The activation energy for crystallization is as high as 312.6 kJ·mol?1 obtained by Kissinger and Ozawa analyses. The values of Avrami exponent (n) imply that the crystallization is dominated by interface-controlled three-dimensional growth in the early stage and the end stage and by diffusion-controlled two- or three-dimensional growth in the middle stage. In addition, the amorphous Al₇₂Ni₈Ti₈Zr₆Nb₃Y₃ powders were sintered under 2 GPa at temperatures of 673 K and 723 K. The results show that the Vickers hardness of the compacted powders is as high as Hv 1215.     

Effect of Nb on the corrosion behavior of continuous bulk metallic glass-coated steel wire composites

(Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5)_100?xNb_x (at%, x=0 and 8) bulk metallic glasses (BMGs) were coated on the surface of Q195 steel wires by a continuous coating process. The potentiodynamic polarization tests of these BMGs were conducted in 3.5wt% NaCl aqueous solution. It is found that the addition of 8at% Nb into Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 alloy results in the improvement of corrosion resistance with the pitting potential of ?52 mV, the open circuit potential of ?446 mV, and the corrosion current density of 9.86×10?6 mA/cm2. This may be attributed to that Nb is beneficial to passivate and stabilize Zr and Ti.     

Effect of proton irradiation on structure relaxation of Zr<Subscript>41.5</Subscript>Ti<Subscript>14.9</Subscript>Cu<Subscript>12.6</Subscript>Ni<Subscript>10.5</Subscript>Be<Subscript>20.4</Subscript> bulk metallic glass

Effects of proton irradiation on structure re-laxation of Zr_(41.5)Ti_(14.9)Cu_(12.6)Ni_(10.5)Be_(20.4) bulk metallic glass areinvestigated by means of X-ray diffraction, differential scan-ning calorimetric and electronic resistance measurements.The results show that, at 203 K, the structure ofZr_(41.5)Ti_(14.9)Cu_(12.6)Ni_(10.5)Be_(20.4) bulk metal glass is relaxed obvi-ously by proton irradiation with the energy and the dosebeing of 160 keV and 1.65×10~(16) ions/cm~2, respectively. How-ever, Zr_(41 .5)Ti_(14.9)Cu_(12.6)Ni_(10.5)Be_(20.4) bulk metallic glass becomesmore steady amorphous state under two conditions, one isthat the energy and the dose are 160 keV and 1.1×10~(15)ions/cm~2, respectively. Another is that the energy and thedose are 120 keV and 6.5×10~(15) ions/cm~2, respectively.     

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.     

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.     

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.     

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.     

Effects of density difference of constituent elements on glass formation in TiCu-based bulk metallic glasses

Glass formation is generally favored by a large atomic size mismatch among constituent elements,which usually leads to large density differences among them as well.During melting,elemental segregation occurs due to Stokes’ law and then inevitably affects glass formation.In this paper,such effects on glass-forming ability in a TiCu-based alloy system have been demonstrated.In the bulk glassforming composition Ti43Cu42Hf14Si1,macroscopic segregation of Si was observed in the as-melted ingots and silicon was completely depleted in the as-cast rods.In another Ti33Cu47Ni8Zr11Si1 alloy,nevertheless,the effects of density differences among the constituent elements were less severe.It was also confrmed that using proper pre-alloys could be an effective way in alleviating the side effects of the elemental segregation.     

Effects of crystallization on corrosion behaviours of a Ni-based bulk metallic glass

The effects of microstructure change on the corrosion behaviours of Ni₅₅Nb₂₀Ti₁₀Zr₈Co₇ bulk glass-forming alloy were investigated in 1 mol/L HCl and 0.5 mol/L H₂SO₄ solutions. Different microstructures of the Ni-based alloy were achieved by annealing the bulk glassy rod prepared by copper mould casting. The microstructure, grain size, grain distribution, and phase composition were characterized. Electrochemical behaviours of the Ni-based alloy were revealed by static immersion and anodic potentiodynamic polarization tests. It is indicated that the corrosion behaviours of the Ni-based bulk glass-forming alloy are related to its microstructures, while the fully crystallized alloy exhibits a relatively lower corrosion resistance than those of the amorphous states.     

Synthesis,structure and mechanical properties of Zr-Cu-based bulk metallic glass composites

The unusual glass-forming ability (GFA) of the Zr₄₈Cu₃₆Ag₈Al₈ alloy and the high ductility of the Zr₄₈Cu₃₆Ag₈Al₈ metallic glass-matrix composites containing Ta powder were reported. The bulk metallic glass rod with a diameter of 25 mm was successfully synthesized using copper mold casting for the Zr₄₈Cu₃₆Ag₈Al₈ alloy. High GFA of this alloy was found to be related to a large supercooled liquid region and a quaternary eutectic point with low melting temperature. The bulk metallic glass matrix composites were prepared by introducing extra Ta particles into the Zr₄₈Cu₃₆Ag₈Al₈ melt. The composites consist of Ta particles homogenously distributed in the Zr₄₈Cu₃₆Al₈Ag₈ metallic glass matrix. The optimum content of Ta powder is 10at% for the composite with the highest plasticity, which shows a plastic strain of 31%.     

Compositional dependence of thermal and elastic properties of Cu-Ti-Zr-Ni bulk metallic glasses

Starting from the quaternary Cu₄₇Ti₃₄Zr₁₁Ni₈ alloy, the compositional dependence of thermal and elastic properties of Cu-Ti-Zr-Ni alloys was systematically investigated. Quaternary Cu-Ti-Zr-Ni alloys can be cast directly from the melt into copper molds to form fully amorphous strips or rods with the thickness of 3–6 mm. The evidence of the amorphous nature of the cast rods was provided by X-ray spectra. The measured glass transition temperature (T_g) and crystallization temperature (T_x) were obtained for the alloys using differential scanning calorimetry (DSC) at the heating rate of 20 K/s. In the results, the differences between the glass temperature and the crystallization temperature (ΔT_x=T_x-T_g) are measured with values ranging up to 33–55 K. The reduced glass transition temperature (T_rg), which is the ratio of the glass temperature to the liquidus temperature (T_l), is often used as an indication of the glass-forming ability of metallic alloys. For the present Cu-Ti-Zr-Ni alloys, this ratio is typically in the range of 0.5838–0.5959, characteristic of metallic alloys with good glass-forming ability. The elastic constants for several selected alloys were measured using ultrasonic methods. The values of the elastic shear modulus, bulk modulus, and Poisson’s ratio were also given.     

Work toughening effect in Zr_（41）Ti_（14）Cu_（12.5）Ni_（10）Be_（22.5） bulk metallic glass

Work hardening is a well-known phenomenon occurring in crystalline metals during deformation,which has been widely used to increase the strength of metals although their ductility is usually reduced simultaneously. Here we report that the plastic strain of Zr41Ti14Cu12.5Ni10Be22.5 (at.%) bulk metallic glasses has been increased from 0.3% for the as-cast sample to 2.5%-8.0% for samples that have experienced pre-deformation under constrained conditions. The pre-deformed glassy alloys possess more free volume and abundant introduced shear bands,which are believed to promote the activation of shear bands in post-deformation and result in an increase in plasticity. The orientation of the pre-introduced shear bands relative to the loading direction will affect the deformation behavior of pre-deformed samples. The present results show that pre-deformation of this glassy alloy will result in work toughening. This work toughening effect can be removed by isothermal annealing at a sub-Tg (glass transition) temperature,which causes annihilation of free volume and healing of shear bands.     

Annealing crystallization and catalytic activity of ultrafine NiB amorphous alloy

Annealing crystallization of ultrafine NiB amorphous alloy prepared by the chemical reduction method was studied by DTA, XRD and XAFS techniques. The XRD and XAFS results have revealed that the crystallization process of ultrafine NiB amorphous alloy proceeds in two steps. First, ultrafine NiB amorphous alloy is crystallized to form metastable nanocrystalline Ni₃B at an annealing temperature of 325℃. Second, the nanocrystalline Ni₃B is further decomposed into crystalline Ni at 380℃ or higher tempera ture, the local structure around Ni atoms in resultant product is similar to that in Ni foil. It was found that the catalytic activity of nanocrystalline Ni₃B for benzene hydrogenation is much higher than that of ultrafine NiB amorphous alloy or crystalline Ni. The result indicates that the active sites of nanocrystalline Ni₃B for benzene hydrogenation are composed of both Ni and B with proper geometry configuration.     

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.