Zr-Ni Metallic Glasses Research Articles

Study on the mechanism of crystal-induced plasticity enhancement in Ni-Zr crystal/amorphous composites by molecular dynamics simulation

The industrial applications of metallic glass (MGs) are limited by poor plasticity, which crystal/amorphous composites (CACs) can effectively address. This study simulates the compression of Ni-Zr MGs with embedded fcc crystal phases by molecular dynamics to elucidate the mechanism of crystal-induced plasticity enhancement. The plasticity of CACs improves with larger crystal sizes. Atoms at the crystal-amorphous interfaces (CAIs) are classified as CAIfcc and CAIMGs for fcc and MGs, respectively. The transformation of CAIfcc to CAIMGs at the CAIs is crucial for plastic flow during compression. The connection between CAIfcc and CAIMGs clusters is less stable than that of fcc, making it more prone to damage and leading to multiple shear bands (SBs). These SBs offer additional pathways for plastic flow, reducing stress concentration and enhancing material plasticity. This research provides an atomic-level understanding of crystal-induced plasticity in CACs, offering valuable insights for designing high-performance CACs.

In-situ TEM study of oxygen-modulated crystallization pathway in Ni-Zr metallic glass

Clarifying the crystallization path, from the thermodynamic point of view, is of importance for the structure and properties of metallic glasses (MGs). The influence of oxygen on the crystallization pathway of Ni65Zr35 MG was investigated by in-situ heating transmission electron microscopy (TEM). As temperature increases, crystalline Ni7Zr2 and t-ZrO2 phases are formed first rather than the Ni10Zr7 and Ni21Zr8 phases, which are the main crystallization products following the phase diagram. Oxygen changes the crystallization pathway by varying the Ni/Zr ratio, indicating that the effects of oxygen on the crystallization in nanometer-sized MG cannot be neglected even in high vacuum TEMs.

Comparing short–range and medium–range ordering in Cu[sbnd]Zr and Ni[sbnd]Zr metallic glasses – Correlation between structure and glass form ability

According to recent studies, CuZr and NiZr binary alloying systems are very similar based on known glass-forming ability criteria, however, they exhibit significant difference in glass-forming ability in practice. In this work, local atomic structures of CuZr and NiZr metallic glasses are studied by molecular dynamics simulation to explain the source of mentioned difference. The total and partial distribution functions, coordination number and voronoi analysis are utilized to characterize the local atomic structures around Zr, Ni and Cu atoms. It was found that the local environment around Zr atoms is almost similar in both systems. The difference in the atomic structure in these systems mainly arises from topologies of polyhedra around Cu and Ni atoms. In particular, full icosahedron is one of the most popular local structure in CuZr system, while its population is significantly smaller in NiZr system with the same composition. Additionally, networks formed by full icosahedra connections, medium range order, are more robust in CuZr system. Higher percentage of topologically ordered and compact structures and their connectivity could explain why bulk metallic glass formation is possible in CuZr system but not in NiZr system.

Atomistic simulation of effects of surface notches and loading mode on deformation and mechanics of ZrNi metallic glass

The effects of surface notches and loading mode on the mechanical deformation and mechanics of ZrNi metallic glass (MG) are studied using molecular dynamics simulations based on the many-body embedded-atom potential. The effects are investigated in terms of atomic trajectories, shear strain distributions, and stress-strain curves. The simulation results show that for ZrNi MG, resistance to shear deformation (shear strain > 200%) before breaking is much greater than that to tensile and compressive deformation. For ZrNi MG under tension, a pre-existing notch leads to earlier necking and breaking. Significant stress concentration occurs around the notch root when the notch length (L) is 3 nm or above, and dominates plastic deformation. For ZrNi MG under compression, a pre-existing notch is completely filled by neighboring atoms at the initial stage of compression. A pre-existing notch leads to single-edge barreling and weakens a sample’s ultimate strength when the L value is 3 nm or above. For ZrNi MG under shear loading, a pre-existing notch does not influence the shear modulus of samples; however, their ultimate strength decreases with increasing L value.

Electronic structure and glass forming ability in early and late transition metal alloys

A correlation between the change in magnetic susceptibility (Δχexp) upon crystallisation of Cu–Zr and Hf metallic glasses (MG) with their glass forming ability (GFA) observed recently, is found to apply to Cu–Ti and Zr–Ni alloys, too. In particular, small Δχexp, which reflects similar electronic structures, ES, of glassy and corresponding crystalline alloys, corresponds to high GFA. Here, we studied Δχexp for five Cu–Ti and four Cu–Zr and Ni–Zr MGs. The fully crystalline final state of all alloys was verified from X-ray diffraction patterns. The variation of GFA with composition in Cu–Ti, Cu–Zr and Cu–Hf MGs was established from the variation of the corresponding critical casting thickness, dc. Due to the absence of data for dc in Ni–Zr MGs their GFA was described using empirical criteria, such as the reduced glass transition temperature. A very good correlation between Δχexp and dc (and/or other criteria for GFA) was observed for all alloys studied. The correlation between the ES and GFA showed up best for Cu–Zr and NiZr2 alloys where direct data for the change in ES (ΔES) upon crystallisation are available. The applicability of the Δχexp (ΔES) criterion for high GFA (which provides a simple way to select the compositions with high GFA) to other metal-metal MGs (including ternary and multicomponent bulk MGs) is briefly discussed.

Atomistic Simulation of ZrNi Metallic Glasses Under Torsion Test

ZrNi metallic glass alloy nanowires (NWs) under torsion are studied using molecular dynamics simulations based on the many-body embedded-atom potential. The effect of cooling rate on the deformation mechanism and mechanical properties of ZrNi NWs is evaluated in terms of shear strain, torque, potential energy and radial distribution function. Simulation results show that for slower cooling rates, the NWs have larger packing density, whereas for faster cooling rates, the packing density of atoms decreases. The amount of deformation increases with increasing torsional angle before it reaches a critical torsional angle ([Formula: see text]. The torque required for deformation and the [Formula: see text] value increase with decreasing cooling rate, indicating a larger mechanical strength. Localized shear bands concentrate at regions with high shear strains, leading to the formation of torsional buckling.

Structural Signature of Plasticity Unveiled by Nano-Scale Viscoelastic Contact in a Metallic Glass.

Room-temperature plasticity in metallic glasses (MGs) is commonly associated with local structural heterogeneity; however, direct observation of the subtle structural change caused by plasticity is vitally important but the data are extremely scarce. Based on dynamic atomic force microscopy (DAFM), here we show that plasticity-induced structural evolution in a Zr-Ni MG can be revealed via nano-scale viscoelastic contacts between an AFM tip and plastically deformed MG surface layers. Our experimental results clearly show a spatial amplification of the nano-scale structural heterogeneity caused by the distributed plastic flow, which can be linked to the limited growth, reorientation and agglomeration of some nano-scale energy-absorbing regions, which are reminiscent of the behavior of the defect-like regions with non-affine deformation as conceived in many theories and models. Furthermore, we are able to experimentally extract the thermodynamic properties of these nano-scale regions, which possess an energy barrier of 0.3–0.5 eV, about half of that for a typical shear transformation event that usually occurs at the onset of plasticity. The outcome of our current work sheds quantitative insights into the correlation between plasticity and structural heterogeneity in MGs.

Atomic-scale simulation to study the dynamical properties and local structure of Cu-Zr and Ni-Zr metallic glass-forming alloys.

Molecular dynamics simulation with well-developed EAM potentials was carried out to investigate the transport properties and local atomic structure of Cu-Zr and Ni-Zr metallic glasses and supercooled liquids. It is found that Cu or Ni atoms have much faster dynamics than Zr atoms in relaxation timescales, while Zr atoms display faster dynamics in the Cu-Zr system than in the Ni-Zr system. A dynamical crossover phenomenon from Arrhenius to super-Arrhenius behavior in the transport properties was observed for the Cu65Zr35 system at Tx ≈ 1250 K and the Ni65Zr35 system at Tx ≈ 1500 K, respectively. Further structural analysis suggests that the dominant interconnected clusters in Cu65Zr35 and Ni65Zr35 systems are 〈0, 0, 12, 0〉, 〈0, 1, 10, 2〉, 〈0, 2, 8, 2〉 and 〈0, 3, 6, 4〉. To directly characterize and visualize the correlated dynamics, we regard the full icosahedra as the microscopic origin responsible for the formation of metallic glasses in the Cu65Zr35 system, while the metallic glass formation in the Ni65Zr35 system can be attributed to the slow dynamics of 〈0, 3, 6, 4〉, 〈0, 2, 8, 2〉 and 〈0, 1, 10, 2〉 Ni-centered Voronoi polyhedra. The local atomic order and dynamics for Cu65Zr35 and Ni65Zr35 systems are remarkably different, and these differences are presumed to hinder crystal nucleation and growth, hence promoting the largely different bulk glass-forming ability.

Vibrational Properties of Zr–Ni Metallic Glasses

Present paper deals with a theoretical investigation of the vibrational properties of Zr-Ni metallic glasses (MGs) using theoretical model proposed by Hubbert Beeby. The pair potential is obtained through Wills Harrison (WH) method from our newly constructed parameter free model potential. The present results of phonon dispersion curves of Zr-Ni MGs are compared with the available MD results and others available data. The elastic properties such as longitudinal sound velocity (υL), transverse sound velocity (υT), bulk modulus (B), modulus of rigidity (G) and Young’s modulus (Y) have also been calculated from the elastic part of the Phonon dispersion curve (PDC). Finally, a comparison is made between the present results and available theoretical data which are found in good agreement.

Extrinsic mechanical size effects in thin ZrNi metallic glass films

Mechanical size effects in ZrxNi100−x thin metallic glass films are investigated for thicknesses from 200 to 900nm. Local order, elastic properties and rate sensitivity are shown to be thickness independent, while hardness and fracture resistance are not. The increase of hardness with decreasing thickness is related to the substrate constraint on shear banding. Fracture surfaces exhibit a corrugated morphology, except for thickness below 400nm exhibiting perfectly flat surfaces. The corrugations appear again on the thinnest films when adding a cap layer, indicating that the fracture mechanisms are primarily dominated by the loading configuration and geometry which constrain the plastic zone extension. Increasing the Ni content from 25% to 58% leads to an increase of elastic modulus, Poisson ratio, strength, activation volume, and fracture toughness. These changes can be understood based on the change in thermodynamic fragility and Zr–Ni bonds formation. Zr75Ni25 composition shows exceptionally large rate sensitivity exponent equal to 0.058. The fracture mechanisms are not modified by composition and the fracture toughness is systematically low due to the confinement of the plastic zone.

High-pressure effects on Ti–Zr–Ni metallic glass and its corresponding quasicrystal

The room-temperature high-pressure effects on Ti38Zr38Ni24 metallic glass and its corresponding icosahedral quasicrystal have been investigated by in-situ angle-dispersive synchrotron radiation. It is demonstrated that the thermodynamic metastable metallic glass and icosahedral quasicrystal retain their structures up to 42.9 and 46.0GPa, respectively. For the Ti38Zr38Ni24 quasicrystal, disorders are likely developed during compression. However, no special behaviors are detected in its amorphous counterpart although thermal analyses suggest that the metallic glass is possibly in microquasicrystalline nature.

Fractal growth of the dense-packing phase in annealed metallic glass imaged by high-resolution atomic force microscopy

Unlike crystalline metals, which have a well-understood periodical structure, the amorphous structure of metallic glasses (MGs) is still poorly understood, particularly when such a structure rearranges itself at the nanoscale under external agitations. In this article, we provide compelling evidence obtained from a recently developed high-resolution atomic force microscopy (HRAFM) technique that reveals the nanoscale structural heterogeneity after thermal annealing in a Zr–Ni metallic glass. Through the HRAFM technique, we are able to uncover the annealing-induced fractal growth of the dense-packing phases in the binary MG thin film, which exhibits a fractal dimension of ∼1.7, in line with a two-dimensional diffusion limited aggregation process. The current findings not only reveal the evolution process of atomic packing in the annealed MG thin film, but also shed light on the possible cooling rate effect on the atomic structure of MGs.

Relationship between amorphous structure and corrosion behaviour in a Zr–Ni metallic glass

The effect of amorphous structure on corrosion is a long-term puzzling problem. To elucidate this relationship, a Zr2Ni metallic glass and its single crystal counterpart were selected, in which they are both homogeneous in composition and structure. The corrosion behaviour has been evaluated in 0.1M NaCl aqueous solution. Compared with the single crystal, the amorphous alloy presents a higher corrosion resistance. The passive film formed on the amorphous alloy contains more ZrO2 and less NiO content. These results reflect that the amorphous structure could effectively influence the composition and compactability of passive films.

Irreversible rearrangements and fertile regions in deformed metallic glasses

The present study is based on the use of numerical methods to simulate the response of model Ni–Zr metallic glasses to shear deformation. Individual atoms were artificially displaced one at a time to perturb local atomic arrangements. In various cases, the artificial atomic displacements induced a local irreversible rearrangement of the positions of small groups of atoms. The minimum displacement length activating the rearrangement provides a measure of the relative mechanical stability of the group of atoms against deformation. It is shown that the metallic glasses include regions characterized by particularly high degrees of mechanical instability, and then more prone than others to deformation-induced rearrangements. These fertile regions are present in undeformed metallic glasses as a consequence of the quenching process. The shear deformation induces a gradual decrease of their mechanical stability and finally their rearrangement. At the same time, deformation also promotes the formation of new fertile regions. Whereas quenching results in fertile regions uniformly distributed in the metallic glass volume, the fertile regions formed by deformation tend to concentrate in the central portion of the simulated system.

Structural origin of the different glass-forming abilities in ZrCu and ZrNi metallic glasses

Abstract

Glass-forming ability and atomic-level structure of the ternary Ag–Ni–Zr metallic glasses studied by molecular dynamics simulations

Based on the recently proposed long-range empirical potential formulism, an n-body potential is constructed for the Ag–Ni–Zr ternary metal system and verified to be realistic by reproducing some important properties of the pure metals as well as of some equilibrium compounds of the system. Applied the constructed Ag–Ni–Zr potential, molecular dynamics simulations and Voronoi tessellations are then carried out to study the effect of alloying composition on glass-forming ability and atomic-level structure of the ternary Ag–Ni–Zr metallic glasses. For the Ag50−x/2 NixZr50−x/2 alloys, with increasing Ni concentration, distortion of the crystalline structure becomes significant, implying a disordering process going on, and at the same time, the number of {0, 0, 12, 0} icosahedrons increases remarkably and the {0, 0, 12, 0} icosahedrons are almost Ni-centered. When the Ni concentration is increased up to 20 atom %, the ternary Ag–Ni–Zr solid solution collapses and turns into a disordered state, suggesting that increasing the Ni concentration could enhance the glass-forming ability of the system. For the Ag30Ni40Zr30 ternary metallic glass, it is found that most of the polyhedrons with coordinate number (CN < 13) are Ni-centered, whereas most of polyhedrons with CN > 14 are either Ag or Zr centered.

Structural, Transport, and Magnetic Characterization of NiZr Metallic Glasses with varied Ni/Zr composition

ABSTRACTThree families of NixZry (x = 28, 36, 38, x + y = 100%) metallic glasses were prepared and examined using X-ray, temperature dependent transport and magnetic field. X-ray characterization shows characteristic diffuse spectrum, except for narrow regions of control samples, where partial crystallization was induced in finite small volumes. Magnetic properties confirm spin-fluctuating paramagnetic-like behavior, which we asses from preliminary Hall coefficient measurements, which is quantitatively different in three sample families. Temperature dependent AC and DC transport measurements were conducted in a broad temperature range from 70 K to 700 K, finding both quantitative and semi-qualitative differences between samples with different Ni/Zr ratio.

Equation of state and topological transitions in amorphous solids under hydrostatic compression

Equation of state (EoS) relating volume and pressure or other thermodynamics state variables is well-established in crystalline systems, but remains rather incomplete in structurally disordered materials such as metallic glasses. Recent experiments and calculation show that the EoS in some amorphous metals exhibits constitutive behavior deviating significantly from that predicted from many well-established EoS, suggesting fundamentally different mechanisms in operation. But due to the lack of long-range order, it is difficult to uncover the underlying atomic process directly from experiment. Here we report a systematic investigation of the constitutive response of a model ZrNi metallic glass under hydrostatic compression by using extensive molecular dynamics simulation. We show that at low-pressure, the EoS is dominated by large decrease in the excess volumes, presumably those of the valence electrons; and at high-pressure, hardcore repulsion takes over. The two is bridged by a polymorphic topological transition occurring in close association with Ni, one of the alloy elements with much lower compressibility and rigid neighbor bonds that exhibit the topological transition in both short and medium-range. The complex and detailed topological rearrangement reported here may form the general underlying mechanism for the EoS of many metallic glasses composed predominately of metals with different compressibility, such as early and late transition metals and some rare-earth metals. The necessity of the electronic structural change thought to be responsible for some reported EoS is discussed also in light of this work.

On the atomic structure of Zr–Ni and Zr–Ni–Al metallic glasses

Using real space pair distribution functions derived from high precision x-ray diffraction data, the local atomic structure of Zr–Ni and Zr–Ni–Al metallic glasses was investigated. Unlike Zr–Cu metallic glasses, the structure of Zr–Ni metallic glasses cannot be approached with an ideal solution model, due to strong attractive interactions between Zr and Ni atoms, which promote chemical short range order. Addition of Al can be beneficial for the glass forming ability of Zr–Ni metallic glasses. The atomic size of Al, being intermediate to those of Zr and Ni and the strongly attractive interactions between Zr–Al and Zr–Ni atoms can lead to highly negative volumes of mixing ΔVmix, and to denser atomic structures, reduced atomic mobility in the liquid and easier suppression of crystallization in the undercooled liquid state

Local atomic structures in Zr–Ni metallic glasses

Local atomic structures of Zr 100 − x Ni x ( x = 33.3 , 36, 50 at%) binary metallic glasses were investigated by means of extended X-ray absorption fine structure (EXAFS) probe. Structural parameters show that the Zr–Ni bond length, R Zr – Ni , keeps a constant value of 2.62 Å, regardless of alloy compositions. This result implies that there is a strongly chemical interaction between Zr and Ni atoms, leading to significant chemical short-range orders (CSROs) in the present metallic glasses. Further analysis indicates that the SRO structures in these metallic glasses are extremely similar with those in their crystalline counterparts. It is interesting to note that the CSROs in the eutectic Zr 64Ni 36 metallic glass consist of Zr 2Ni-like and ZrNi-like CSROs.