Zr55Cu30Al10Ni5 Bulk Metallic Glass Research Articles

Thermodynamics and corrosion properties of nitrogen doped zirconium-based bulk metallic glasses

The effect of adding N on the thermodynamics and corrosion resistance of as-cast Zr55Cu30Ni5Al10 bulk metallic glass (BMG) is clarified using electrochemical measurements, microstructure characterization and surface analyses. Compared with Zr55Cu30Ni5Al10 BMG, Nitrogen-doped (Zr55Cu30Ni5Al10)98.5N1.5 BMG is easier to nucleate during heating, but the nucleation growth process becomes more difficult. The corrosion potential (Ecorr) of (Zr55Cu30Ni5Al10)98.5N1.5 BMG and Zr55Cu30Ni5Al10 BMG is −0.32 V and −0.39 V respectively, and the corrosion current density (Icorr) of (Zr55Cu30Ni5Al10)98.5N1.5 BMG and Zr55Cu30Ni5Al10 BMG is 7.90 × 10−8 A/cm2 and 9.13 × 10−5 A/cm2, respectively. I.e., after nitrogen doping the corrosion potential increased slightly, but the corrosion current density decreased by about three orders of magnitude. Meanwhile the oxide film resistance increased significantly, and the surface corrosion diffusion effect weakened. Nitrogen reduces the H+ concentration in the pitting pits, slows down the pitting rate, and improves the corrosion resistance. Proper nitrogen can improve the thermal-stability and surface corrosion resistance of Zr-based BMGs.

Tensile behavior of large size Zr−based bulk metallic glass composites prepared by selective laser melting

A Zr55Cu30Al10Ni5 (Zr55) bulk metallic glass composite (BMGC) with a size of 37 × 37 × 10 mm3 was fabricated by using selective laser melting (SLM) additive manufacturing technology with argon gas atomized (GAed) powder. The microstructure and tensile deformation behavior of SLMed Zr55 BMGCs are investigated. The microstructure evolution perpendicular to the laser scan direction exhibits a periodic microstructure with three different zones (amorphous, nanocrystal + amorphous and dendritic eutectic + nanocrystal zones). The stepwise tensile fracture behavior, mixing ductility with a sharp stress drop after the failure of amorphous layers is shown for the Zr55 BMGC. The nanocrystal + amorphous crystalline zone has a lower hardness and elastic modulus than the amorphous zone via the nanoindentation test, therefore, the stress drops obviously when the hard amorphous layers fail and then stress recovery follows as the soft crystalline layers pick up the load, resulting in a final failure strain of 9%. The results further verified the feasibility of SLM technology for the development of high−performance BMGCs for industrial applications.

Rejuvenation by compressive elasto-static loading: The role of static stress on a Zr-based metallic glass

Calorimetric, mechanical, and microstructural characterizations are used to investigate the rejuvenation of Zr55Cu30Al10Ni5 (at%) bulk metallic glass (BMG) by elasto-static loading (ESL). The as-cast BMG samples are compressed at room temperature for 24 h while being subjected to static stresses that ranged from 40 %, 70 %, 80 %, and 90 % of the yield stress. The BMG undergoes structural rejuvenation as a result of the compressive ESL treatment, increasing the free volume content at all applied static stresses. The amount of energy that has been stored, as determined by the relaxation exotherms that precede glass transition, appears to be a function of static stress and reaches a maximum of 13.2 J g−1 at the highest applied stress, which is twice the stored energy of the as-cast sample. A steady increase in plastic strain, a decline in hardness, and a fall in Young's modulus are linked to enthalpy rejuvenation of the BMG. According to microstructural investigations, ESL introduces structural heterogeneities into the BMG that are linked to structural dilatation at the short- and medium-range atomic scales. This study emphasizes rejuvenation as the main effect of ESL treatment on the BMG under study.

The effect of impurities in zirconium on the formation and mechanical properties of Zr55Cu30Al10Ni5 metallic glass

Minor alloying has been developed as an effective method to modify and optimize various properties of bulk metallic glasses (BMG). In this work, as inevitable minor alloying elements, two major impurities, hafnium (Hf) and oxygen (O) were quantitatively confirmed to co-exist in two zirconium (Zr) raw materials with different grades of impurities. The effects of these two impurities on the thermal properties, crystallization behavior, glass-forming ability (GFA), and mechanical properties of the nominal Zr55Cu30Al10Ni5 BMG were systematically studied. The O impurity was found to promote the formation of the Al5Ni3Zr2 intermetallic compound phase, which could account for the poor GFA, thermal stability, and plasticity associated with BMGs with higher O content in the Zr raw material. In contrast, although the impurity of Hf has a much higher content than O, a negligible effect of Hf on the Zr55Cu30Al10Ni5 BMG was revealed. These findings were further confirmed by deliberately adding extra O and Hf with designed contents into the Zr55Cu30Al10Ni5 BMG. Our results clarify the effects of different impurities in Zr raw materials on the Zr-based BMG and will help guide industrial production and applications of Zr-based BMGs.

Composition optimization of Zr55Cu30Al10Ni5 bulk metallic glass using cluster formula approach

Compositions of typical binary and ternary bulk metallic glasses have previously been interpreted via a cluster formula approach, i.e., a good glass former is formulated by a nearest-neighbor cluster matched with one or three glue atoms, with a free electron number per unit formula approaching 24. In this study, a classical quaternary glass composition Zr55Cu30Al10Ni5, representative of bulk metallic glasses of complex chemistry and dual-glassy structure, is interpreted and optimized using a dual-cluster formula approach, i.e., a chemical formula representing two single-cluster formulas. First, the number of atoms in the dual-cluster formula is estimated from combinations of all possible single-cluster formulas of the major devitrification phase CuZr2, which ranges from 28 to 34. Second, the free electron number of each element is estimated using the Cu-Zr single-cluster formulas. Third, the reference composition Zr55Cu30Al10Ni5 is approximated into integer forms of 27 to 36 atoms and their free electron numbers are calculated using the assigned free electron numbers of the elements. The so-formulated compositions are examined for glass forming abilities via copper-mold arc melting. The atomic densities, the critical temperatures, the HV hardness, the volume fractions of the glassy phase in the ingots, and the activation energies of crystallization all point to a 32-atom chemical formula Zr17Cu10Al3Ni2 (Zr53.13Cu31.25Al9.38Ni6.25) as the optimal glass former, with its electron number per unit formula falling slightly below 48. This work confirms the 24-electron rule for single-cluster formulas and provides an easy route towards understanding the complex chemistries of bulk metallic glasses via multiple single-cluster formulas.

Comment on “Berkovich nanoindentation of Zr55Cu30Al10Ni5 bulk metallic glass at a constant loading rate”, J. Non-Cryst. Solids, 561 (2021) 120750

It is argued that the decrease with increasing indenter load in the value of the elastic modulus [1] of a bulk metallic glass determined using a nanoindentation machine combined with the current methods of data analysis is not a manifestation of any damage in the metallic glass. Rather, the cause of the decrease of the elastic modulus is an error in the method of data analysis.

Interface characterization in tungsten fiber/Zr-based bulk metallic glass matrix composite

In this research, Zr55Cu30Al10Ni5 bulk metallic glass (BMG) alloy is used as the base material to form tungsten fiber reinforced BMG composites. The composites are synthetized using melt infiltration casting method and their microstructure and compressive properties are investigated. Two different infiltration times of 10 min and 15 min are used to produce the composites. The microstructural evaluation of the interface between tungsten fiber and BMG matrix reveals that a narrow reaction band emerges between the tungsten wires and BMG alloy. Some portions of this layer are broken into the fine Zr/W-rich particles and eventually are dispersed in the BMG matrix, when the infiltration time is 15 min. The results also showed that increasing the infiltration time from 10 min to 15 min improves the compression strength of the composite from 1333 MPa to 1396 MPa and also increases the compression strain of the composite from 0.11 to 0.13. This is attributed to the lack of porosities and better metallurgical bonding between tungsten fibers and BMG matrix.

Berkovich nanoindentation of Zr55Cu30Al10Ni5 bulk metallic glass at a constant loading rate

Berkovich nanoindentation experiments were conducted on Zr55Cu30Al10Ni5 bulk metallic glass under a constant loading rate. Indentation hardness decreased linearly with contact depth, which defied the direct application of conventional indentation size effect model for crystalline material. Elastic modulus remained invariant under small loads, but decreased linearly under large loads. The scaling relationships between indentation variables such as contact depth, permanent depth, the maximum indentation displacement, plastic energy, the total work of indentation and their ratios were investigated. The area of shear band circle, the projected contact area at the maximum load, and the residual projected area were all found to be proportional to one another. A new methodology to determine fracture toughness was proposed based on the total work of indentation, provided that the critical indentation displacement at the onset of fracture corresponds to zero value of elastic modulus extrapolated from curve fitting.

Expanding the homogeneous regime of deformation in bulk metallic glass by electromigration-induced rejuvenation

The origin of plasticity in bulk metallic glasses (BMGs) is highly elusive due to their complicated amorphous atomic structures. Nonetheless, there is a general consensus that the homogeneous regime of deformation on the deformation map of BMGs is constrained by high temperature and low strain rate. Here we report an expanded homogeneous regime in a Zr55Cu30Al10Ni5 BMG, which is achieved by applying a pulsed electric current to the BMG specimen subjected to external loading. The BMG specimen exhibits homogeneous elongation and necking, rather than shear banding as it should without pulsed current. The results indicate that the pulsed current produces an additional effective “temperature increment” ∼0.15Tg (Tg, the glass transition temperature) apart from the Joule heating effect. This expanded homogeneous regime is attributed primarily to electromigration-induced dynamic rejuvenation which promotes homogeneously distributed deformation by enlarging the shear transformation zones. These findings could benefit understandings of plasticity in glassy materials.

The brittleness of post-treatment of 3D printed Zr-based metallic glasses in supercooled liquid state

3D printed technique of selective laser melting (SLM) has attracted great attention in fabricating bulk metallic glass (BMG) due to its superiority on fabrication of large-sized BMGs with desirable geometries. However, compared to traditional casting BMGs, 3D printed BMGs present brittleness due to annealing effect in 3D printing process. Rejuvenation treatment in supercooled liquid state was expected to improve the plasticity by increasing free volume in amorphous phases. Here, 3D printed Zr55Cu30Al10Ni5 BMG was selected to perform heat treatment. The results reveal that both molten pool and heat affected zone are gone soft after heat treatment because of the increasing free volume in amorphous phases. However, tiny micro-cracks induced by non-uniform thermal deformation during quenching process deteriorate the macroscopic mechanical properties. The present work provides an understanding on heat treatment to 3D printed BMG that free volume can be introduced successfully and soften the amorphous phases, but need a suitable cooling rate to restrain micro-cracks.

Fabrication of a Zr-based bulk metallic glass surface with extreme wettability

Unlike the high surface energy of traditional metallic materials, metallic glass with amorphous structure have a lower surface energy with a different wettability of solid surfaces. In this work, the micro-nano hierarchical structures were constructed on the Zr55Cu30Ni5Al10 bulk metallic glass (BMG) surface by electrochemical corrosion and then modified with stearic acid to form both superhydrophobic and superlipophilic surfaces. After the optimized modification conditions, the water contact angle was as high as 169.6 ± 3.5° with a low water sliding angle of 5° and the contact angle of oil on the alloy surface was 5°, respectively. The present work would open a window for the application of bulk metallic glasses in nondestructive liquid transportation and oil-water separation.

Differences in surface mechanical properties of Zr-based bulk metallic glass related to stress condition

Differences in surface mechanical properties of Zr55Cu30Al10Ni5 bulk metallic glass (BMG) was revealed through indentation tests. Inhomogeneous stress condition was constructed through fabricating asymmetrical double V-notches. Indentation responses at various locations along with and perpendicular to the connection line between the notch tips indicated a significant difference in surface hardness with range from 1.012 GPa to 1.463 GPa, corresponding to a tensile stress ranging from 11.8 MPa to 246.3 MPa. The stress gradients induced by prefabricted notches cased the anisotropy of residual indentation morphologies. Furthermore, selected area electron diffraction analysis adjacent to the notch tip exhibited typical halo ring and amorphous state, which indicated that the morphological anisotropy and differences in indentation responses were mainly caused by inhomogeneous stress and Poisson effect rather than local crystallization behaviors.

Cyclic stress induced surface nanocrystallization adjacent to indentation edge of Zr-based bulk metallic glass at room temperature

Crystallization behaviors of bulk metallic glass (BMG) have been obtaining widespread concern, especially under service conditions including elevated temperature, electrical pulse, mechanical stress and high pressure. In this paper, cyclic stress was considered as typical service condition and applied on a Zr55Cu30Al10Ni5 BMG specimen with prefabricated double V-notches. Through indentation tests on fatigue-fractured specimen along with the connection line between notch tips, diversities in indentation serrated flow behaviors and morphological anisotropies were directly observed. Through transmissionelectronmicroscopy (TEM) characterization and selected area electron diffraction (SAED) analysis of thinned BMG specimen adjacent to indentation edge, direct experimental evidence of local crystallization at room temperature (RT) was verified. Meanwhile, the distance-dependent crystallization behavior was investigated in terms of gradually increased quantity of diffraction spots and precipitated nanocrystalline adjacent to indentation edge. Furthermore, high resolution transmission electron microscopy (HRTEM) images and SAED patterns at identical indentation microregion of tensile-fractured BMG specimen did not exhibit obvious nanocrystalline and diffraction spots, which indicated that the cyclic stress rather than static stress induced surface crystallization adjacent to indentation edge at RT.

Crystallization behavior of Zr55Cu30Al10Ni5 amorphous alloys produced by selective laser melting of preannealed powders

Selective laser melting (SLM) of Zr55Cu30Al10Ni5 (Zr55) bulk metallic glasses (BMGs) with Zr55 original unannealed powders and annealed powders has been investigated, which is an effort to reveal the influence of crystallization state of powders on the crystallization behavior of remelted zone (RZ) and heat affected zone (HAZ). The as-prepared Zr55 powders consist of amorphous matrix and Al5Ni3Zr2-type phase. When the Zr55 origin powders are annealed at 600 K, 800 K and 1000 K, the microstructure of amorphous matrix is transformed into amorphous, metastable + stable phases and entirely stable phases, respectively. After SLM of these different powders, the gradient microstructure with three crystalline zones (nanocrystal, dendritic eutectic, spherulite) is found from RZ to HAZ for all the deposits. However, the size and density of dendritic eutectic in the top of HAZ is much smaller for the deposits prepared by annealed powders than that by the unannealed powders. In contrast to top of HAZ, abundant multiphase spherulites are formed at the bottom of HAZ for the deposits prepared by the powders with or without annealed. The detailed microstructural and numerical model results reveal that the crystallization at the top of HAZ is mainly dominated by the rapid growth of quench-in clusters or nuclei in RZ, but the crystallization at the bottom of HAZ is controlled by both the nucleation and growth of these clusters or nuclei. It is precisely because the average size of quench-in clusters or nuclei increases but total quantity decreases during annealing, resulting in the increase of thermal stability in RZ and the suppression of crystallization in the top of HAZ for the deposits with annealed powders.

Complexity analysis of serrated flows in a bulk metallic glass under constrained and unconstrained conditions

For the present work, the Zr55Cu30Ni5Al10 (atomic percent) bulk metallic glass underwent room-temperature compression experiments in both the constrained and unconstrained conditions. For the constrained condition, samples were exposed to strain rates ranging from 2 × 10−5 s−1 to 2 × 10−3 s−1, while for the unconstrained case, the rates varied between 5 × 10−5 s−1 and 2 × 10−3 s−1. The serrated flow was modeled and analyzed using the refined composite multiscale entropy algorithm. Findings indicate that the complexity of the serration behavior increased with respect to the strain rate for both conditions. The increase in the complexity with increasing the strain rate is thought to be linked to a rise in the number of defect interactions that occur in the alloy during plastic deformation. Results also indicate that for a strain rate of 2 × 10−3 s−1, the complexity of the serrated flow was the highest in the constrained condition, which corresponds to higher spatiotemporal correlations between slipping weak spots during a serration event. The microscopy results combined with the complexity analysis support the idea that the serration events, which correspond to defect interactions, are more spatially correlated in the constrained condition.

Effects of Nb minor addition on atomic structure and glass forming ability of Zr55Cu30Ni5Al10 bulk metallic glass

This work aims to show Nb micro-alloying role on structural changes and glass forming ability (GFA) of Zr55Cu30Ni5Al10 bulk metallic glass. Pair distribution function (PDF) analysis indicates that the minor Nb addition forms Nb-centered clusters at the short range scale. It is also revealed that the atomic rearrangement happens in the medium range order and loosely-packed structure changes to a densely-packed one. This means that the clusters tend to form interpenetrating structures at the medium range scale. This event is related to the strong interaction of Zr and Nb elements in the material. Moreover, the thermal analyses demonstrate that the sample with Nb has a greater super-cooled liquid region and better GFA. The relaxation enthalpy decreases in the Nb-content sample which is due to the formation of denser clusters at short range scale and a structural shrinkage at the medium range order of the bulk metallic glass.

Role of tensile elastostatic loading on atomic structure and mechanical properties of Zr55Cu30Ni5Al10 bulk metallic glass

In this work, the pre-tensile elastostatic loading with low stress values (5%–20% σy) was used to rejuvenate Zr55Cu30Ni5Al10 bulk metallic glass (BMG). The atomic pair density function analysis shows that the rejuvenation evolution is accompanied with a significant disordering of short and medium atomic scales in the BMG structure. The results also indicate that the decreasing rate of annihilation in CuZr pairs under rejuvenation is higher than ZrZr and ZrAl pairs. In general, it is suggested that the interaction of stress domains under elastostatic loading is the main reason for disordering during the rejuvenation evolution. The compression test reveals that a brittle-to-ductile transition is happened from as-cast sample to the rejuvenated ones. Moreover, it is found that the serrations in the plastic region of stress-strain curves of highly-rejuvenated samples show a self-organized critical state. As a whole, with increase in pre-tensile elastostatic loading value, the structural rejuvenation enhances and the homogeneous plasticity improves.

Novel Crystallization Behaviors of Zr-Based Metallic Glass Under Thermo-Mechanical Coupled Fatigue Loading Condition

Novel crystallization behaviors of Zr55Cu30Al10Ni5 bulk metallic glass are investigated. On the one hand, mixed oxides, including CuO, CuAlO2, CuAl2O4 and ZrO2, show sequential oxidation process determined by coupling effects of specific cyclic load and temperature. On the other hand, at a temperature (100 °C) by far lower than Tg of 412 °C, under cyclic loading condition, non-oxidized binary alloy CuZr2 is precipitated; the thermo-mechanical coupled effects of temperature below Tg and fatigue accumulation on the non-oxidized crystallization behaviors are revealed. Meanwhile, at a constant temperature of 400 °C, by comparing among the XRD patterns, respectively, obtained from tensile, creep and fatigue fractures, the dominating effect of cyclic load on the generation of non-oxidized CuZr2 is verified. Furthermore, the crystallization behavior of amorphous phases under cyclic loading condition is observed through TEM micrograph and diffraction pattern at 100 °C.

Extra rejuvenation of Zr55Cu30Al10Ni5 bulk metallic glass using elastostatic loading and cryothermal treatment interaction

This work reports the feasibility of extra rejuvenation in a ZrCuAlNi bulk metallic glass (BMG) under combination of cryothermal treatment and tensile elastostatic loading in low stresses. Pair distribution function analysis shows that the annihilation of Cu-centered clusters as well as the increase in population of Al-centered clusters and intensification of spatial connectivity are signs of rejuvenation evolution under cryothermal treatment. On the other side, tensile elastostatic loading leads to an extensive disordering through the both short range and medium range scales. The maximum stored energy values with cryothermal treatment and elastostatic loading in the BMG were 0.52 and 0.73 Kj/mol, respectively. The combination of two mentioned processes on a BMG sample also indicates that the material can inherit the characteristics of structural changes which are caused by both cryothermal treatment and tensile loading altogether. This event generates an extra stored energy in the metallic glass (0.92 Kj/mol).

Annealing-assisted high-pressure torsion in Zr55Cu30Al10Ni5 metallic glass

For bulk metallic glasses (BMGs) structural anisotropy has been studied for many years, but usually for small creep strains, rather than for large strains associated with the viscoplastic flow. In this study, the structural modifications in the short-to-medium range order of Zr55Cu30Al10Ni5 BMG is deliberated for the first time upon simultaneous high-pressure torsion (HPT) and in-situ annealing around the glass transition temperature (Tg). The changes are evaluated in terms of hardness by microindentation, thermal properties by differential thermal calorimetry, chemistry by energy dispersive X-ray, and structural properties by synchrotron X-ray diffraction and transmission electron microscopy. A remarkable increase of the glass transition temperature and the absence of the shoulder of the crystallization peak along with remarkable softening and shear thinning reveals that even at Tg the material gains flow characteristics because of the extreme pressure applied. A clear shift towards smaller wave vector Q in the peak positions of the partial distribution function G(r), and reconfiguration of the bonding between Zr−Zr and Zr−Cu atomic pairs extracted from the deconvolution of the radial distribution function RDF(r) are observed with changing the processing temperature. The findings give insight into the atomic and nano-scale modifications in BMGs due to high-pressure torsion at different temperatures which would be essential to tune the intrinsic properties of BMGs to attain the desirable hardness and thermal stability for a specific application.