Deformation behavior of Zr60.0Al15.0Ni25.0 metallic glass

The effect of thermal crystallization on viscous flow of supercooled liquid in Zr₆₀Al₁₅Ni₂₅ metallic glass was investigated. Zr₆Al₂Ni crystalline precipitates with ellipsoidal morphology appeared during thermal annealing and deformation at high temperatures. No significant difference in phase selection or morphology of crystalline precipitates was observed between non-deformed and deformed specimens. The viscous flow behavior is very sensitive to the strain rate and the stress–strain behavior can be classified into three types depending on the strain rate: stress overshoot mode, stable viscous flow mode with constant flow stress, and strain hardening mode. The strain hardening is caused by the precipitation of Zr₆Al₂Ni phase from supercooled liquid. The flow stress increased with increase in the crystallization ratio for specimens containing a volume fraction of Zr₆Al₂Ni phase higher than 10% although the stress showed no significant change with slight crystallization.     

Electron irradiation induced phase transformation in Zr66.7Cu33.3 and Zr66.7Pd33.3 metallic glass

Crystallization and phase selection in Zr_66.7Cu_33.3 and Zr_66.7Pd_33.3 metallic glass during thermal annealing and electron irradiation were examined. During thermal annealing an equilibrium C11_b–Zr₂Cu phase directly precipitated in the amorphous phase of Zr_66.7Cu_33.3 metallic glass while a thermal equilibrium C11_b–Zr₂Pd phase formed after icosahedral quasi-crystalline phase precipitation in Zr_66.7Pd_33.3 metallic glass. The amorphous phase was not stable under electron irradiation and metastable crystalline phases with face-centered cubic-based structure formed in both kinds of metallic glass by electron irradiation induced crystallization. The unique phase selection in electron irradiation induced crystallization is due to a change in the phase stability of crystal, quasi-crystal and amorphous phase under electron irradiation.     

Crystallization of amorphous Zr60Al15Ni25 alloy

The phase formation and crystallization kinetics during the thermal treatment of amorphous Zr₆₀Al₁₅Ni₂₅ alloy were investigated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). By lowering the isothermal annealing temperatures, it is revealed that the crystallization of the amorphous Zr₆₀Al₁₅Ni₂₅ alloy consists of a primary transformation followed by a polymorphic transformation, corresponding to the precipitations of hexagonal Zr₆Al₂Ni and the Zr₅AlNi₄ with a U₃Si₂-typed superstructure. The primary phase being Zr₆Al₂Ni rather than Zr₅AlNi₄ in the crystallization is because the latter has a complex structure and its formation requires the diffusion of Al and Zr atoms on a large scale.     

Influence of oxygen on the crystallization behavior of Zr65Cu27.5Al7.5 and Zr66.7Cu33.3 metallic glasses

The influence of oxygen on the crystallization behavior of Zr_65−xCu_27.5Al_7.5O_x (x=0.14, 0.43 and 0.82) and Zr_66.7−xCu_33.3O_x (x=0.14 and 0.82) metallic glasses has been studied. The supercooled liquid regime (ΔT_x) decreases with increase in oxygen content for the Zr–Cu–Al alloy, while it increases for the Zr–Cu metallic glass. In the case of the Zr–Cu metallic glass, the crystallization product (Zr₂Cu) is not influenced by the oxygen content, while in Zr–Cu–Al alloys the oxygen level has a strong influence on the crystallization sequence. At low oxygen level (x=0.14), the ternary glass crystallizes polymorphously to Zr₂(Cu,Al). At higher oxygen content, the ternary amorphous alloy crystallizes in two stages by primary crystallization into an icosahedral phase and subsequently to the stable Zr₂(Cu,Al) phase. Three-dimensional atom probe results have shown that the composition of the icosahedral and amorphous phases is close to Zr₇₅Cu₁₅Al₅O₅ and Zr₆₂Cu₂₄Al₁₄, respectively.     

Phase stability of amorphous and crystalline phases in melt-spun Zr66.7Cu33.3 alloy under electron irradiation

Effect of electron irradiation on structural change of Zr_66.7Cu_33.3 alloy was examined. Metastable nanocrystalline f.c.c.-Zr₂Cu phase precipitated from the amorphous phase by electron irradiation, while b.c.t.-Zr₂Cu phase was crystallized by thermal annealing. The crystalline b.c.t.-Zr₂Cu phase was transformed to the nanocrystalline f.c.c.-Zr₂Cu phase through the amorphous state during electron irradiation.     

Microstructural analysis of Zr55Cu30Al10Ni5 bulk metallic glasses by laser surface remelting and laser solid forming

The crystallization behavior of Zr₅₅Cu₃₀Al₁₀Ni₅ bulk amorphous alloy during laser solid forming (LSF) was analyzed. Since laser surface remelting (LSM) is a key process for the LSF, the crystallization behavior of as-cast Zr₅₅Cu₃₀Al₁₀Ni₅ bulk metallic glasses (BMGs) during LSM was also investigated. It was found that the amorphous state of the as-cast BMGs was maintained when they were repeatedly remelted four times in a single-trace LSM, and as for the LSF of Zr₅₅Cu₃₀Al₁₀Ni₅ bulk amorphous alloy, the crystallization primarily occurred in the HAZ between the adjacent traces and layers after the two layers were deposited. The as-deposited microstructure exhibited a series of phase evolutions from the molten pool to the HAZ as follows: the amorphous → NiZr₂–type nanocrystal + amorphous → NiZr₂–type equiaxed dendrite + amorphous → Cu₁₀Zr₇–type dendrite + NiZr₂–type nanocrystal. Among these microstructural patterns, the NiZr₂–type nanocrystals and equiaxed dendrites primarily formed from the rapid solidification of the remelted liquid in the laser processing process, and the Cu₁₀Zr₇–type dendrites in the HAZ primarily formed by the crystallization of pre-existed nuclei in the already-deposited amorphous substrate.     

Crystallization behavior of the Zr63Al7.5Cu17.5Ni10B2 amorphous alloy during isothermal annealing

The crystallization behavior of Zr₆₃Al_7.5Cu_17.5Ni₁₀B₂ amorphous Alloy was studied by means of scanning differential calorimetry (DSC), X-ray diffraction (XRD), and transmission electron microscopy (TEM). A single stage transformation of the amorphous phase forming a Zr₂Cu-type crystalline phase was observed. Kinetics for such single stage crystallization was analyzed by means of Johnson–Mehl–Avrami equation and discussed regarding to the value of Avrami exponent. In addition, the cube of crystal size presents a linear relationship with isothermal annealing time. This indicates that the crystallization process of Zr₆₃Al_7.5Cu_17.5Ni₁₀B₂ amorphous alloy belongs to thermally activated process of Arrhenius type. From the HRTEM analysis, small amount of Zr₂Cu-type crystals in the nano-scale dimension (10–20 nm) were observed to precipitate from the amorphous matrix upon the early stage of isothermal annealing the amorphous alloy at the temperature between the glass transition (T_g) and the onset crystallization temperature (T_x).     

Structural and calorimetric evolutions of mechanically-induced solid-state devitrificated Zr60Ni25Al15 glassy alloy powder

A single phase of glassy Zr₆₀Ni₂₅Al₁₅ alloy powder was synthesized by mechanically induced solid-state reaction (MISSR) technique. The MISSR was performed in a room-temperature high-energy ball mill, using a mechanical alloying method. Whereas the glass transition temperature of the obtained glassy alloy is 681 K, the melting and liquidus temperatures are 1179 K and 1256 K, respectively. The mechanically alloyed Zr₆₀Ni₂₅Al₁₅ glassy powders maintain its unique disordered structure through a large supercooled liquid region (99 K). It, however, transforms into a mixture of Zr₅Ni₄Al and Zr₆NiAl₂ crystalline phases at 780 K with a large enthalpy change of crystallization of −81.8 J/g. The possibility of devitrification of the synthetic glassy phase upon increasing the ball milling time was investigated. The results have shown that the glassy powder obtained after 173 ks of milling is subject to heavy lattice imperfections and tends to transform into a metastable-big cube phase after further ball milling times (216–259 ks). After 446 ks of milling, a complete glassy-metastable phase transformation is achieved and the end-product of this stage of milling is nanocrystalline big-cube powders which have a lattice constant of 1.2282 nm. The big-cube Zr₆₀Ni₂₅Al₁₅ phase transforms into the same crystalline mixture of Zr₅Ni₄Al and Zr₆NiAl₂ phases at 799 K with an enthalpy change of transformation of −73.7 J/g. As the milling time increases (720 ks), the obtained big-cube phase can no longer withstand against the shear and impact stresses that are generated by the milling media and surprisingly transformed into a new metastable phase of nanocrystalline fcc- Zr₆₀Ni₂₅Al₁₅. The lattice constant of this metastable phase was calculated and found to be 0.45449 nm. The fcc-metastable phase transforms into a mixture of Zr₅Ni₄Al and Zr₆NiAl₂ crystalline phases at rather a high temperature, as high as 901 K with a heat change of transformation of −24.4 J/g. The reported metastable phase here is new and has never been, so far as we know, reported for ternary Zr-Ni-Al system, or its binary phase relations.     

Corrosion behavior of Zr–Cu–Ni–Al bulk metallic glasses in chloride medium

Polarization and passivation behavior of three Zr-based BMGs, i.e. Zr_58.3Al_14.6Ni_8.3Cu_18.8, Zr₅₈Al₁₆Ni₁₁Cu₁₅ and Zr_57.5Al_17.5Ni_13.8Cu_11.3 were investigated in 3% NaCl aqueous solution. Electrochemical investigations were carried out by potentiodynamic polarization method at room temperature. The corroded sample surfaces were examined using scanning electron microscope having energy dispersive spectroscopy (EDS) attachment. The results of the present investigation revealed that Zr₅₈Al₁₆Ni₁₁Cu₁₅ and Zr_57.5Al_17.5Ni_13.8Cu_11.3 BMGs having relatively larger supercooled liquid region (ΔT_x) and pitting overpotential (η_pit) values exhibit low corrosion current density (i_corr) and corrosion penetration rate (CPR) values.     

Solid state amorphization and crystallization in Zr66.7Pd33.3 metallic glass

We observed quasicrystal-to-amorphous-to-crystal (Q–A–C) transition in Zr_66.7Pd_33.3 metallic glass. The unique disordering–ordering phase transition was induced by 2 MeV electron irradiation at 298 K. Electron irradiation can induce not only the solid-state amorphization but also crystallization of a glassy structure under the same irradiation conditions. The Q–A–C transition can be explained by change in the phase stability of crystal, quasicrystal and amorphous phases by electron irradiation induced atomic displacement.     

Thermal stability and crystallization of Zr–Al–Cu–Ni based amorphous alloy added with boron and silicon

The amorphous Zr_65−x−yAl_7.5 Cu_17.5Ni₁₀Si_xB_y alloy ribbons, x=1–4 and y=1–2, with 0.1 mm thickness were prepared by melt spinning. The thermal properties and microstructure development during the annealing of amorphous alloys were investigated by the combination of differential thermal analysis, differential scanning calorimetry, X-ray diffractometry, and TEM. Both of the glass transition temperature and the crystallization temperature for Zr_65−x−yAl_7.5 Cu_17.5Ni₁₀Si_xB_y alloys increases with the silicon and boron additions and reaches 674 and 754 K, respectively for Zr₆₀Al_7.5 Cu_17.5Ni₁₀Si₄B₁ alloy. The highest T_rg (0.62) and γ value (0.43) occurred at the Zr₆₀Al_7.5Cu_17.5Ni₁₀Si₄B₁ alloy. In addition, the Zr₆₀Al_7.5Cu_17.5Ni₁₀Si₄B₁ alloy was revealed to have the highest activation energy of crystallization (about 370 kJ/mol as determined by the Kissinger plot). This value is about 20% higher than the activation energy of crystallization for the Zr₆₅Al_7.5Cu_17.5Ni₁₀ based alloy (314 kJ/mol). In parallel, the alloy 4Si1B also performs a longer incubation time at higher isothermally annealing temperature. All of the evidence implies that Zr₆₀Al_7.5 Cu_17.5Ni₁₀Si₄B₁ alloy exhibits the highest thermal stability among those alloys in this study. The crystallization behavior for the alloy 4Si1B isothermally annealed at the supercooled temperature region for different time has also been examined by TEM and discussed.     

Nanocrystallization of Zr61Al7.5Cu17.5Ni10Si4 metallic glass

The primary nanocrystallization behavior and microstructural evolution of the Zr₆₁Al_7.5Cu_17.5Ni₁₀Si₄ alloy during annealing were investigated by isothermal differential scanning calorimetry, X-ray diffractometry and transmission electron microscopy. During continuous heating of the 4Si and the base (contains no Si) amorphous alloys at a heating rate of 10 K/min, the saturation point of nucleation for the 4Si amorphous alloy occurs at a crystallization fraction of 78%, which is significantly higher than 65% for the base alloy, implying that these metalloid atoms would extend the nucleation stage and refine crystalline particles. The sequence of crystallization phase from the amorphous matrix for the isothermally annealed 4Si amorphous alloy at 703 K is observed to be Zr₂Cu and Zr₂Ni at the early stage, Zr₃Al at an intermediate stage, and Zr₂Si at the final stage. Moreover, enrichment of Si atoms at the interface between Zr₂Cu crystal and the amorphous matrix is detected. This may result in increasing the thermal stability of the remaining amorphous phase and retardation of the crystal growth of Zr₂Cu particles.     

Electron-irradiation-induced nano-crystallization in quasicrystal-forming Zr-based metallic glass

Phase selection in electron-irradiation-induced crystallization and crystal-to-amorphous-to-crystal (C–A–C) transition at 298 K in quasicrystal-forming Zr–Pt metallic glass alloys were investigated. Two types of f.c.c. nano-crystalline precipitates were formed in amorphous Zr₈₀Pt₂₀ and Zr_66.7Pt_33.3 alloys under electron irradiation; such unique nano-crystalline structures were not observed during thermal annealing. It was inferred that unique phase selection in electron-irradiation-induced crystallization and thermal crystallization can be explained by the large negative chemical mixing enthalpy (ΔH_chem) in Zr–Pd and Zr–Pt alloys.     

Phase equilibrium in the Cu–Ni–Zr system at 800 °C

The isothermal cross-section through the ternary Cu–Ni–Zr phase diagram at 800 °C was constructed by means of diffusion couples and equilibrated alloys. Two ternary phases Cu_20–40Ni_40–60Zr₂₀ and Cu_20–25Ni_60–65Zr₁₅ exist in the system at this temperature. Most of the Cu–Zr and Ni–Zr binary intermetallic phases show large solubility range extending to the ternary region and the solubility ranges are determined. Although Cu₁₀Zr₇ and Ni₁₀Zr₇ binary phase have the same crystal structure oC68, both phases did not form complete solid solution phase. Electron Microprobe analysis was used to determine the phase composition.     

Effect of Ta on glass formation,thermal stability and mechanical properties of a Zr52.25Cu28.5Ni4.75Al9.5Ta5 bulk metallic glass

The effect of Ta on glass-forming ability, crystallization behavior and mechanical properties of Zr_52.25Cu_28.5Ni_4.75Al_9.5Ta₅ bulk metallic glass (BMG) is investigated. The solubility of Ta in the Zr-base BMG alloy depends on the arc melting conditions. 3.2 at.% Ta dissolve in the alloy inducing an increase of about 20 K in both glass transition temperature and crystallization temperature of the BMG. However, Ta does not significantly change the extension of the supercooled liquid region. The remaining Ta particles in the master alloy may induce a composition-segregation layer around the particles upon subsequent casting. This further induces the crystallization of Zr₂Cu that deteriorates the ductility of the samples. The compressive strength and ductility of the as-cast 3 mm diameter Zr_52.25Cu_28.5Ni_4.75Al_9.5Ta₅ samples are improved in comparison with the Zr₅₅Cu₃₀Ni₅Al₁₀ BMG alloy. The fracture plane of the present alloy has an angle of 31–33° with respect to the stress axis, which remarkably deviates from the maximum shear stress plane. The improvement of the mechanical properties and the peculiar fracture feature for the Zr_52.25Cu_28.5Ni_4.75Al_9.5Ta₅ BMG alloy can be attributed to the effect of dispersed Ta particles.     

Influence of powder size on the crystallization behavior during laser solid forming Zr55Cu30Al10Ni5 bulk amorphous alloy

The Zr₅₅Cu₃₀Al₁₀Ni₅ bulk metallic glasses (BMGs) were prepared using laser solid forming (LSF) process from the plasma rotating electrode process (PREP) powder. The effect of the powder size on the crystallization behavior of the remelted zone (RZ) and heat affected zone (HAZ) was investigated. It was found that the as-prepared powders were composed of the amorphous phase and Al₅Ni₃Zr₂-type phase. The RZ mainly kept the amorphous state after LSF. The residual Al₅Ni₃Zr₂-type phase could be observed in RZ only if the powder size was larger than 106 μm. Meanwhile, the NiZr₂-type nanocrystals at the boundary of RZ primarily formed from the solidification of remelted liquid. With the increase of the powder size, the lower overheating temperature and shorter existing time of the molten pool enhanced the heredity of Al₅Ni₃Zr₂ clusters and other intermetallic clusters in remelted alloy melt, which decreased the thermal stability of the already-deposited layer. The volume fraction of crystallization in the deposit increased with the increase in powder size. There was no crystallization occurred in the HAZ between the adjacent tracks and layers for the deposit prepared by the powder with the size range of 53–75 μm. However, the wide crystalline band with Al₅Ni₃Zr₂-type faceted phase, CuZr-type dendrite, CuZr₂-type spherulite and NiZr₂-type nanocrystal were observed in the entire HAZ for the deposit prepared by the powder with the size range of 106–150 μm. The finer powder was benefit to prepare the BMGs by LSF.     

Effects of ion irradiation on Zr52.5Cu17.9Ni14.6Al10Ti5 (BAM-11) bulk metallic glass

Bulk metallic glasses are intriguing candidates for nuclear applications due to their inherent amorphous structure, but their radiation response is largely unknown due to the relatively recent nature of innovations in bulk metallic glass fabrication. Here, microstructural and mechanical property evaluations have been performed on a Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ bulk metallic glass (BAM-11) irradiated with 3 MeV Ni⁺ ions to 0.1 and 1.0 dpa at room temperature and 200 °C. Nanoindentation hardness and Young's modulus both decreased by 6–20% in samples irradiated at room temperature, with the sample irradiated to 1.0 dpa experiencing the greatest change in mechanical properties. However, no significant changes in properties were observed in the samples irradiated at 200 °C, and transmission electron microscopy showed no visible evidence of radiation damage or crystallization following ion irradiation at any of the tested conditions. These results suggest that BAM-11 bulk metallic glass may be useful for certain applications in nuclear environments.     

Room-temperature mechanically induced solid-state devitrifications of glassy Zr65Al7.5Ni10Cu12.5Pd5 alloy powders

The high-energy ball milling technique was employed for synthesizing a single phase of glassy Zr₆₅Al_7.5Ni₁₀Cu_12.5Pd₅ alloy powder, using a room-temperature mechanical alloying method. Whereas the glass transition temperature of the obtained glassy alloy is 683 K, the crystallization temperature is 783 K. The mechanically alloyed Zr₆₅Al_7.5Ni₁₀Cu_12.5Pd₅ glassy powders maintain their unique disordered structure through a large supercooled liquid region (100 K). The possibility of devitrification of the synthetic glassy phase upon increasing the ball milling time was investigated. The results have shown that the glassy powder that is obtained after 173 ks of milling is subjected to numerous lattice imperfections and tends to transform into a metastable big-cube phase after further ball milling (259–432 ks). After 540 ks of milling, a complete glassy–metastable phase transformation is achieved and the end-product of this stage of milling is nanocrystalline big-cube powder that has a lattice constant of 1.2293 nm. As the milling time increases (720 ks), the obtained big-cube phase can no longer withstand the shear and impact stresses that are generated by the milling media and is transformed into a new metastable phase of nanocrystalline fcc-Zr₆₅Al_7.5Ni₁₀Cu_12.5Pd₅. The fcc-metastable phase transforms into a mixture of Zr₂Cu and Zr₆NiAl₂ crystalline phases at rather high temperature, as high as 993 K.     

Thermal and mechanical properties of Cu60−xZr25Ti15Nix bulk metallic glasses with x=0, 1, 3, 5, 7, 9 and 11 at.%

Systematic investigation on thermal and mechanical properties of Cu_60?xZr₂₅Ti₁₅Ni_x bulk metallic glasses with x = 0, 1, 3, 5, 7, 9 and 11 at.% points out that monolithic Cu₅₃Zr₂₅Ti₁₅Ni₇ and Cu₅₁Zr₂₅Ti₁₅Ni₉ bulk metallic glasses containing optimum Ni content of 7 and 9 at.% are effective to enhance both thermal stability of amorphous structure up to 716 K and plastic strain of 2.4% at room temperature. This indicates that a selection of additional elements such as Ni by considering a mixing enthalpy to the constituent elements is very important to control the thermal stability and plasticity. Moreover, it is believed that the addition of minor Ni can be a trigger to form the chemical heterogeneity upon solidification. Such chemical heterogeneity formed by the selection of the minor elements has a strong influence to cause the oscillation of the shear stress by wavy propagation of the shear bands thus leading the improvement of macroscopic plasticity of the bulk metallic glasses.     

Glass forming ability and stability: Ternary Cu bearing Ti,Zr, Hf alloys

Four Cu bearing alloys of nominal composition Zr₂₅Ti₂₅Cu₅₀, Zr₃₄Ti₁₆Cu₅₀, Zr₂₅Hf₂₅Cu₅₀ and Ti₂₅Hf₂₅Cu₅₀ have been rapidly solidified in order to produce ribbons. All the alloys become amorphous after melt-spinning. In the Zr₃₄Ti₁₆Cu₅₀ alloy localized precipitation of cF24 Cu₅Zr phase can be observed in the amorphous matrix. The alloys show a tendency of phase separation at the initial stages of crystallization. The difference in crystallization behavior of these alloys with Ni bearing ternary alloys can be explained by atomic size, binary heat of mixing and Mendeleev number. It has been observed that both Laves and Anti-Laves phase forming compositions are suitable for glass formation. The structures of the phases, precipitated during rapid solidification and crystallization can be viewed in terms of Bernal deltahedra and Frank–Kasper polyhedra.