Zr-based Bulk Amorphous Alloys Research Articles

Effect of high temperature deformation on the deformation behavior and thermodynamic properties of a Zr-based bulk amorphous alloy

Zr 55.7 Cu 22.4 Ni 7.2 Al 14.7 alloy rods with a diameter of 3 mm were prepared by copper mold suction casting. The structure, thermodynamic properties and plastic deformation behavior of the specimens before and after compression in supercooled liquid region were studied by X-ray diffractometer (XRD), differential scanning calorimeter (DSC) and uniaxial compression machine (equipped with a high-temperature oven). The range of thermal forming process parameters was also discussed. The results show that the alloys have obvious glass transition and crystallization kinetics, and the crystallization activation energies obtained by the Kissinger and Ozawa equations are 297.1 kJ/mol and 294.9 kJ/mol, respectively. The amorphous alloys exhibit stress overshoot in low temperature region at high strain rates and deformation behavior of alloy softening in high temperature region at medium to high strain rates. Meanwhile, the viscosity of the alloy remains approximately constant at 740 K and 750 K, showing Newtonian fluid characteristic. It can be concluded that the optimal thermoplastic forming process ranges from 740 K to 750 K, 5 × 10 −4 s −1 to 5 × 10 −3 s −1 . The crystallization activation energies of the specimens after deformation are slightly higher than before, and they increase with the increase of strain rate. • Zr-based bulk amorphous alloy has a good thermodynamic stability, which facilitates thermoplastic forming. • The amorphous alloy shows superplastic deformability at high temperatures and strain rates. • The crystallization activation energies of the deformed specimens are higher than that of the undeformed. • The crystallization activation energies of the alloys after deformation increase with increasing strain rate.

Fast increase in ductility and strength of Zr-based bulk amorphous alloys induced by intermittent high-frequency vibration loading

Intermittent high-frequency vibration loading is introduced into the Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk amorphous alloy as an ultrashort time, easy-to-obtain, nondestructive physical method to adjust its atomic arrangement and shear deformation behavior. It is found that the method of intermittent high-frequency vibration loading can make the ductility and strength of the bulk amorphous alloys increase quickly within 4 s, increasing to 5.3% and 2240 MPa, respectively. And there is a mechanical power threshold of approximately 0.43 kJ/mol. Apart from the as-cast sample, when it is less than this threshold, with the increase of amplitude and pre-pressure, the relaxation enthalpy of IHF-treated samples increases, the ductility increases, but the compressive yield strength is basically unchanged, and there is basically no precipitation of nanocrystals at the same time. When it is greater than the threshold, as the amplitude and pre-pressure increase, the relaxation enthalpy decreases, nanocrystals precipitate, the ductility and the compressive yield strength begin to decrease. Both the increase in free volume content and the appearance of nanocrystals will lead to an increase in the critical stress of the first ejection event, thereby simultaneously increasing the ductility and yield strength. It is also found that the increase in free volume content is the main factor for the increase in ductility and strength, and the appearance of nanocrystals is a secondary factor. Our findings provide a new ultrashort time method for overcoming the strength-ductility trade-off dilemma.

Quasi-static and dynamic deformation behavior of Zr-based bulk amorphous alloy at cryogenic temperature

Quasi-static and dynamic compressive tests with a series loading rates were conducted on (Zr0.6336Cu0.1452Ni0.1012Al0.12)97Tm3 bulk amorphous alloy at cryogenic temperature. It is found that mechanical properties of the alloy such as yield strength and plasticity are obviously dependent on temperature and strain rate. The plastic strain of the specimens at 298 K and 77 K is 8.4% and 13.7% respectively under quasi-static load with strain rate of 1 × 10−4 s−1. Additionally, the dynamic mechanical properties of amorphous alloys at different strain rates were tested by split Hopkinson pressure bar(SHPB) to unveil the dynamic deformation behaviors at cryogenic temperature of 177 K and 77 K. Compared with the results of quasi-static compression, strain rate softening phenomenon can be observed under dynamic loading, but the compressive strength of specimens increases significantly with the decrease of temperature. Moreover, the specimens have no obvious plastic deformation under dynamic loading. Compared with room temperature, the improvement of quasi-static and dynamic compressive strength of the alloy at cryogenic temperature can be attributed to the strong interatomic binding force between the alloy elements.

Comparative studies on the corrosion behavior of some Zr-based amorphous alloys having different compositions in nitric acid medium

The corrosion studies were performed on different composition of Zr-based bulk amorphous ribbon alloys such as Zr55Cu30Ni5Al10, Zr60Nb2Cu20Ni8Al10, Zr59Nb3Cu20Ni8Al10, Zr57Nb5Cu20Ni8Al10 and Zr60Pd5Cu15Ni10Al10 alloys at room temperature. The amorphous nature of all the above mentioned alloys was confirmed by X-ray diffraction (XRD). The corrosion behavior was investigated using potentiodynamic polarization and weight loss analysis methods at room temperature. Surface morphology of these corroded samples were investigated by optical microscopy and scanning electron microscopy (SEM). The results of the investigations revealed the fact that Nb containing Zr-based bulk amorphous alloys shows better corrosion resistance among all the investigated alloys due to the presence of Nb2O5. The presence of Nb2O5 on the surface of Nb containing Zr-based bulk amorphous alloy after immersion in HNO3 medium was confirmed by X-ray photoelectron spectroscopy (XPS) techniques.

Improvement of Mechanical Properties of Zr-Based Bulk Amorphous Alloys by High Temperature Heat Treatment

Zr-based bulk amorphous alloys which were heat-treated from 673 to 1073 K were investigated, and compressive fracture mechanisms related with improvement of mechanical properties were investigated by observing how the type, size and volume fraction of crystalline particles which is generated during the heat treatment affected the fracture mode. The Zr-based bulk amorphous alloys contained nano-sized crystalline particles showed excellent mechanical properties of compressive fracture strength over 2.0 GPa and compressive plastic strain of approximately 1%. The fracture modes of the alloys are changed depending on the heat treatment temperature and their microstructure. When the alloy is heat-treated at 673 K, the nano-sized Zr2Cu particles are generated in amorphous matrix. According to the observation of fractured specimens, in the alloy heat-treated at 673 K, the fine and elongated vein patterns were well developed. The heat treatment temperature increased above Tx, the Zr2Cu particles as well as complex crystalline particles are consist in the heat-treated alloy, which lead to the brittle fracture and the alloy show the low strength of 605 MPa. In the fractured surface of the alloy, large cleavage facets were evenly developed. When the heat treatment temperature up near Tm, the size of Zr2Cu and complex crystalline particles increased to approximately 1 μm and the volume fraction of complex crystalline particles increased up to 52.3%. As the size of crystalline particles change, the size of facet decreased similarly to the size of crystalline particles. Zr-based bulk amorphous alloys which were heat-treated from 673 to 1073 K were investigated, and compressive fracture mechanisms related with improvement of mechanical properties were investigated by observing how the type and size of crystalline particles which is generated during the heat treatment affected the fracture mode. The fracture modes of the alloys are changed depending on the heat treatment temperature and their microstructure. When the alloy is heattreated at 673 K, the nano-sized Zr2Cu particles are generated in amorphous matrix. According to the observation of fractured specimens, in the alloy heat-treated at 673 K, the fine and elongated vein patterns were well developed. The heat treatment temperature increased near Tg, the Zr2Cu particles as well as complex crystalline particles are consist in the heat-treated alloy, which lead to the brittle fracture and the alloy show the low strength of 605 MPa. In the fractured surface of the alloy, large cleavage facets were evenly developed. When the heat treatment temperature up near Tm, the size of Zr2Cu and complex crystalline particles increased to approximately 1 μm.

Strain dependence of diffusion in Zr-based bulk amorphous alloy

We evaluated the effect of strain on the diffusion process of amorphous alloys related to the strain mode in both as-cast and plastically deformed Zr-based bulk amorphous alloy. Experimental investigations of the diffusion process and the elemental distributions in the amorphous alloy were performed by secondary ion mass spectrometry after annealing at 523 K following 30% plastic deformation by multiple cold rolling. Mathematical modeling analyses show an inhomogeneous sequence of the diffusion process by effective strain. The compressive strain near the surface of the deformed amorphous alloy retards ∼13.7% of the diffusion process compared to the as-cast amorphous alloy. The combined experimental and mathematical analyses results reveal that the diffusion process of bulk amorphous alloys can be changed by strain variation and can be adjusted by controlling the effective strain during deformation.

Correlation between Electrical Resistivity and the Structural Evolution of Zr-Based Bulk Amorphous Alloys

The electrical resistivity of three kinds of Zr-based bulk amorphous alloys as a function of continuous increasing temperature was measured by the direct current four-probe method. Combining with Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis, the correlation between the electrical resistivity and structural evolution of these amorphous alloys has been demonstrated. The experimental results showed that three amorphous alloys all had a small negative temperature coefficient of resistivity (TCR<-10-4 K-1) before crystallization. Little change of the electrical resistivity related with the glass transition process was observed, while the electrical resistivity decreased sharply once the crystallization occurred. The onset of crystallization determined by the electrical resistivity measurement was far lower than that by DSC. The different stages of crystallization behavior could be evidently identified by the change of the electrical resistivity.

High-Temperature Sliding Wear Behavior of Zr-Based Bulk Amorphous Alloys

Bulk metallic glasses (BMGs) and their coatings are very attractive for tribological applications because of their high hardness. However, the frictional heat at the contact surfaces causes several effects such as oxidation, viscous flow, and nanocrystallization in the amorphous alloys. High-temperature wear testing offers an excellent way to characterize these effects and transitions in wear mechanisms. In this article, dry sliding wear behavior of the Zr-based BMG (Zr64.13Cu15.75Ni10.12Al10) is investigated in the temperature range of 293 K (room temperature) to 673 K. The wear surfaces showed indications of surface oxidation, viscous flow, formation of a protective layer, and abrasive wear, depending on the wear testing temperature. The Zr-based BMG exhibited the lowest wear rate of 9.7 × 10−4 mm3 m−1 associated with the formation of the protective surface layer at 473 K. With wear testing near glass transition temperature (574–673 K), the profuse crystallization of the surface seemed to change the wear mechanism to abrasive wear, resulting in the breaking of the protective layer and a high wear rate.

Effect of cast process and microalloying on the fracture toughness of Zr-based bulk amorphous alloys

In order to clarify the effects of tilt- or suction-cast processing and microalloying of minor Si on the three-point bending fracture toughness of the Zr-based bulk metallic glasses (BMGs), the tilt-cast and suction-cast Zr53-based and Zr48-based BMGs with and without Si were studied. The results revealed that the tilt-cast specimens present much better fracture toughness than the suction-cast counterparts as a result of their lower degrees of residual porosity. In addition, the microalloying of Si to 0.75at.% in these BMGs would impose negative effects on their fracture toughness. The highest fracture toughness of 120MPam was achieved for the tilt-cast Zr53Cu30Ni9Al8. Moreover, the morphology of fracture surface, the calculated fracture energy, and the Poisson’s ratio show the similar trend to prove that the tilt-cast Zr-53 BMG without Si possesses the best fracture toughness among these BMGs in this study.

Stable reflectivity of bulk metallic glass mirrors for ITER optical diagnostic through an irradiation-induced self-recovery mechanism

Reflection mirrors or first mirrors for ITER diagnostic are subjected to intense irradiations that deteriorate the reflectivity of the diagnostic mirrors. In the present study, the reflective optical properties of bulk metallic glasses Co61.2B26.2Si7.8Ta4.8, Zr65Al7.5Ni10Cu17.5 and Zr63.7Al9.0Ni27.3 after being exposed to hydrogen sputtering and helium erosion were compared to those of polycrystalline Mo and W. Surface structure and specular reflectivity of the mirrors were characterized before and after the exposures. Compared to polycrystalline Mo, W and Zr-based bulk amorphous alloys Zr65Al7.5Ni10Cu17.5 and Zr63.7Al9.0Ni27.3, no significant changes in specular reflectivity were observed for the mirror made from the Co–B-based bulk amorphous alloys Co61.2B26.2Si7.8Ta4.8 after the exposures. The initial surface crystallization of the bulk metallic glasses after a short influx of ions is shown to reverse to amorphization upon further bombardments, unveiling an erosion-induced self-recovery amorphization mechanism that guarantees stable surface structures and henceforth stable reflectivities.

The Effect of Purity of Zirconium Material on Mechanical Properties and Microstructure of Zr-Based Bulk Metallic Glass

Series of rod samples of Zr55Al10Ni5Cu30 alloy were prepared by magnetic suspend melting and copper mold suction casting method using 99.9wt% high purity zirconium and 99.4wt% low purity sponge zirconium respectively, the effect of purity of zirconium material on mechanical properties and microstructure of Zr-based bulk metallic glass were investigated. The result shows that high purity material alloy could enhance the thermal stability and glass forming ability of Zr-based bulk amorphous alloy, compression fracture surface analysis indicate that the vein patterns density increase with the material elements purity increase, the average compressive fracture strength is increased to 8.52% than that of low purity samples.

Surface modification of Zr-based bulk amorphous alloys by using ion irradiation

Surfaces of the [Zr 0.65Cu 0.18Ni 0.09Al 0.08] 98M 2 (M = Er and Gd) bulk amorphous alloys were modified by irradiation with energetic singly charged argon (Ar +) ions. Samples of both the alloys were irradiated with 2.17 × 10 17 argon ions of 10 keV energy. As cast and ion irradiated samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Mechanical properties like Vicker's hardness, nanohardness, elastic modulus and elastic recovery were measured. Considerable increase in elastic modulus and hardness was observed because of ion irradiation in these alloys. The ion irradiated samples of the [Zr 0.65Cu 0.18Ni 0.09Al 0.08] 98Er 2 alloy showed better properties as compared to [Zr 0.65Cu 0.18Ni 0.09Al 0.08] 98Gd 2 alloy. CuZr 2 phase was detected in ion irradiated alloys by XRD and confirmed by EDS. The range of Ar + ions was found to be approximately 9.3 ± 5.4 nm in both alloys.

Dynamic tensile response of Zr-based bulk amorphous alloys: Fracture morphologies and mechanisms

Plate impact experiments were conducted to examine the dynamic tensile response of Zr-based bulk amorphous alloys (BAAs) having a nominal composition of Zr56.7Cu15.3Ni12.5Nb5.0Al10.0Y0.5. The experimental configuration used in our work permitted soft recovery of the samples to allow a careful examination of the fractured samples along with real-time measurements of the sample free-surface velocity (FSV) histories. Tensile loading was preceded by elastic compressive loading to peak stresses in the 3.6 to 6.0 GPa range. Tensile damage in the recovered samples was examined using optical and electron microscopy. The microscopy results showed that the BAA samples exhibit a brittle behavior (as a glass) at the macroscopic level and a ductile behavior (as a metal) at the microscopic level; in addition, corrugations and bumps are observed at the nanoscale. The observed fracture morphologies are related to three key features present in our spall experiments: preceding compressive stress (3.6–6.0 GPa), high tensile loading rate (∼106/s), high mean tensile stress (∼2.3 GPa); and are intrinsically related to the amorphous glassy structure of the BAAs (free volume content). We propose that the compressive stress depletes the free volume content. With increasing compressive stress, the available free volume decreases causing a suppression of shear stresses during tension. Thus, the mean tensile component becomes more dominant at higher stresses. Consequently, the observed surface morphology results from brittle cleavage, causing an increased damage localization in the recovered samples spalled at higher stresses. These observations support the inferences made from measurements of FSV histories. The high tensile loading rate is proposed to be responsible for cracking by multiple shear band propagation and interception, rendering the observed serrated surface morphology. Finally, we proposed that the corrugations are created due to a succession of arrest and propagation of mode I cracks. A subsequent dilatation, due to the effect of the tensile mean stress, caused the corrugations to evolve to bump-type features with sizes in the range of 10–100 nm. Our proposed mechanisms, although qualitative, constitute a systematic attempt to provide an explanation for the fracture morphologies observed in spalled BAA samples.

Processing, Characterization and Properties of Specially Constituted Zr-Based Bulk Amorphous Alloys

Bulk metallic glasses (BMGs) are an emerging class of materials. The amorphous alloys have very attractive properties. There is potential for applications. The quaternary and pentanery (ZrCuAlNi)100-xTix (x = 0, 2 and 5 at. %) alloys were synthesized by melting 2-3N pure metals in an arc furnace. Amorphous ingots were produced using Cu mold casting technique. The alloys showed wide supercooled liquid region Tx, high thermal stability and good glass-forming ability (GFA). Many thermal parameters like Trg, , , β and  were measured employing high temperature differential scanning calorimetry (DSC). Structural characterization was carried out by X-ray diffraction (XRD) technique. Microstructural characterization was conducted using high resolution field emission scanning electron microscopy (FESEM) and elemental analysis was done using energy dispersive spectroscopy (EDS). Crystallization behavior and phase formation was studied. Activation energy for crystallization was calculated using Kissinger and Ozawa equations. The alloys show double stage crystallization. Mechanical properties were measured. Compression test was carried out and fracture strength and strain were determined. The fracture behavior was studied which showed veins like patterns, shear bands formation and liquid droplets.

Evolution of microstructure in Zr 55Cu 30Al 10Ni 5 bulk amorphous alloy by high power pulsed Nd:YAG laser

In this work surface modification of Zr-based bulk amorphous alloy Zr 55Cu 30Al 10Ni 5 was carried out with pulsed Nd:YAG laser. The as-cast and modified surface of amorphous alloys at different conditions were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) techniques. Phases like Cu 10Zr 7, CuZr 2 and NiZr 2 were identified which result in the enhancement of hardness of the modified alloys surface. It was observed that low laser power and prolonged irradiation time provides large nucleation frequency and limited growth rate which intern produces small spherical particle dispersion homogeneously distributed in an amorphous matrix resulting significant increase in surface hardness.

Synthesis and mechanical properties of Zr-based bulk amorphous alloys

Design and characterization of bulk amorphous alloys has been an active area of research due to their promising thermal and mechanical properties. An alloy composition Z65Cu17Ni10Al8 was designed and synthesized by Cu mold casting. In the base alloy 2at.% Gd was added to study its effect on thermal and mechanical properties. Characterization of the alloys was done by techniques of X-ray diffraction (XRD), differential scanning calorimetry (DSC) and field emission scanning electron microscopy (FESEM). Many thermal parameters were evaluated to investigate the thermal stability and glass-forming ability of the alloys. In addition, the mechanical properties like nanohardness, elastic modulus and elastic recovery were measured. Thermal properties and activation energy reduced while mechanical properties like nanohardness, elastic modulus and percentage elastic recovery (% R) increased with Gd addition.

Electron irradiation damage and the recovery in a Zr-based bulk amorphous alloy Zr55Cu30Al10Ni5

Zr-based bulk amorphous alloys have been intensively studied because of their superiority in mechanical properties, corrosion resistance and micro-formability, and of great anticipation of their applications. The damage was introduced into a Zr-based bulk amorphous alloy Zr55Cu30Al10Ni5 by electron irradiation below 20K. The thermal recovery process from the irradiation damage was studied by using positron lifetime spectroscopy which sensitively detect open volume defects. The introduced damage was completely recovered at the temperature lower than the glass transition temperature by 200K. On the other hand, the X-ray diffraction pattern shows no crystalline peaks even after the recovery of the irradiation damage. This result is considerably different from the previous reports studied in conventional amorphous alloys.

Impurity-Driven Nanocrystallization of Zr-Based Bulk Amorphous Alloys

The effect of oxygen content and Ti addition on the glass forming ability (GFA) and crystallization kinetic of Zr-based bulk glass forming alloys have been studied by means of thermal analysis and X-ray diffraction techniques. Presence of oxygen triggers the formation of a nanocrystalline metastable f.c.c. Zr2 Ni-type phase which can act as heterogenous nucleation sites for the formation of dendrites during solidification. An increase in oxygen content changes the crystallization behaviour from a single- to a double-step process and triggers the crystallization of stable Zr2(Cu,Al) besides metastable Zr2 Ni-type phase. Oxygen-triggered nucleation of a nanocrystalline metastable Zr2 Ni-type phase is found to be the initial step of crystallization. The important parameters of GFA such as glass transition temperatures, Tg, the crystallization temperatures, Tx, and crystallization enthalpies, deltaH, were determined by using DSC. It was observed that the presence of oxygen, even in a very small amount, and Ti addition cause a drastic reduction of the supercooled liquid region, deltaTx, accompanied by a change of the crystallization kinetic. This leads to the decrease in stability of the supercooled liquid, consequently results in a deterioration of the glass forming ability of the alloy.

Potentiodynamic polarization studies on amorphous Zr46.75Ti8.25Cu7.5Ni10Be27.5, Zr65Cu17.5Ni10Al7.5, Zr67Ni33 and Ti60Ni40 in aqueous HNO3 solutions

Potentiodynamic polarization studies were carried out on virgin specimens of Zr-based bulk amorphous alloys Zr46.75Ti8.25Cu7.5Ni10Be27.5 and Zr65Cu17.5Ni10Al7.5, and conventional-type binary amorphous alloys Zr67Ni33 and Ti60Ni40 in solutions of 0.2M, 0.5M and 1.0M HNO3 at room temperature. The values of the corrosion current density (Icorr) for the bulk amorphous alloy Zr46.75Ti8.25Cu7.5Ni10Be27.5 were found to be comparable with those of Zr65Cu17.5Ni10Al7.5 in 0.2M and 0.5M HNO3, but the value of Icorr for the former was almost three times more than that of the latter in 1.0M HNO3. In the case of conventional binary amorphous alloys, Ti60Ni40 showed lower value of Icorr as compared to Zr67Ni33 in 0.5M and 1.0M HNO3 and a comparable value of Icorr in 0.2M HNO3. In general, the binary Ti60Ni40 displayed the best corrosion resistance among all the alloys in all the cases and the corrosion current density (Icorr) for all the alloys was found to increase with the increasing concentration of nitric acid. It is noticed that the bulk amorphous alloys do not possess superior corrosion resistance as compared to conventional binary amorphous alloys in aqueous HNO3 solutions. The observed differences in their corrosion behavior are attributed to different alloy constituents and composition of the alloys investigated.

Effect of hafnium incorporation on the crystallization and mechanical behavior of a Zr-based bulk amorphous alloy

The crystallization and mechanical behavior of a hafnium-containing bulk amorphous alloy (Hf 28.35Zr 28.35Cu 15.3Ni 12.5Nb 5.0Al 10.0Y 0.5) was investigated and compared with a Hf-free alloy (Zr 56.7Cu 15.3Ni 12.5Nb 5.0Al 10.0Y 0.5) to understand the role of hafnium. Although the overall behavior of both alloys has similarities both in the as-received and heat-treated states, details of the physical, thermal, and mechanical properties are influenced by the incorporation of hafnium. Differential scanning calorimetry (DSC) results for the hafnium-containing alloy showed a glass transition at 440 °C and three exothermic peaks at 511, 559, 664 °C which correspond to primary and secondary crystallization. The increase in glass transition and the first crystallization temperature, compared to the Hf-free alloy, indicates stabilization of the amorphous state. Samples were heat-treated at various temperatures to examine the crystallization of various intermetallic phases. The phases were identified using X-ray diffraction (XRD) and the sizes varied between 100 and 200 nm, as observed by field emission scanning electron microscopy (FESEM), for samples heat-treated at 700 and 800 °C. The Vickers microhardness increased with heat-treatment from 5.2 to 7.2 GPa. Quasi-static compression tests showed decrease in failure stresses from 1843 MPa (as-received) to 994 MPa (heat-treated at 535 °C). The failure stress increased to 1661 MPa for the sample heat-treated at 800 °C, similar to the Hf-free alloy. Fracture morphologies changed from typical vein-type in as-received samples to smooth facets in heat-treated samples indicating embrittlement. Failure mechanism changes from shear banding in the as-received amorphous samples to void formation and coalescence in the heat-treated samples.