Mechanical Properties Of Amorphous Alloys Research Articles

Shear band evolution and mechanical behavior of cold-rolled Zr-based amorphous alloy sheets: An in-situ study

Cold rolling process can regulate the microstructure and mechanical properties of amorphous alloys, but it is still a challenging task to reveal their microscopic mechanism. Here, we designed an in-situ SEM observation device for the cold rolling process of amorphous alloy, and visually observed the formation and evolution of shear bands during single-pass and multi-pass rolling process of the Zr55Cu30Al10Ni5 amorphous alloy sheets. It is found that the evolution process of shear bands in the rolling process of amorphous alloy shows heritability, which is mainly reflected in two aspects: one is that the shear band formation pattern in the single-pass rolling process is more inclined to inherit the previous shear band formation pattern; the other is that the shear deformation is more likely to occur in the pre-existing shear bands in the multi-pass rolling process. This rule can be used to guide the controlled generation of shear bands in amorphous alloys. Moreover, we emphasized the importance of pre-existing shear band orientations and systematically investigated the mechanical behavior of the amorphous alloys with pre-existing shear bands by in-situ SEM observation. It is found that the mechanical properties of the as-rolled amorphous alloys are determined by the competition between the work-softening of the pre-existing shear band itself and the work-hardening caused by the blocking effect of the pre-existing shear bands on the shear deformation. Based on this, we enhance the tensile fracture strength and the tensile ductility of the amorphous alloy by adjusting the orientation of the pre-existing shear bands parallel to the tensile stress axis so that the pre-existing shear bands prevent the linear propagation and destruction of the new shear bands.

Effect of structural disorder on the oxidation of Zr-based amorphous alloys: A focused review

Structural disordering leads to outstanding mechanical properties of amorphous alloys. Many properties are strongly related to formation of surface oxide layers. An in-depth understanding of effect of structural disordering of amorphous alloys on oxide evolution is essential for applications. This paper presents a review of recent comparative oxidation studies of Zr-based amorphous and single-phase crystalline counterpart alloys. Three representative model alloy systems are selected: Zr–Cu and Zr–Al representing alloys with components of different and similar oxygen affinities, respectively, and Zr–Cu–Al representing multi-component alloys. In combination with molecular dynamic simulations, the fundamental role of the structural disordering of parent alloys in the oxidation processes is revealed. The oxidation of Zr–Cu–Al–Ni amorphous alloys at the supercooled liquid temperature region is further reviewed to clarify the relationship between oxidation and substrate crystallization.

The effect of crystalline structure on the mechanical behavior in Zr-based amorphous materials: A molecular dynamics simulation

The structure relaxation in the Zr-based amorphous phase affects the microstructure and mechanical properties of metallic glasses. To clarify the mechanical properties and deformation mechanism of amorphous crystallization, the compression and tensile deformation of the Zr90Cu10 amorphous model with different levels of ordered lattice structure were studied by molecular dynamics simulation. The influence mechanism of crystals on the deformation and mechanical properties of amorphous alloys was investigated using atomic-scale stress‒strain curves, atomic structures, and dislocation line distributions. The results show that the in situ crystallization of amorphous alloys has a positive effect on enhancing the elastic modulus and yield strength of amorphous metals. The high-stress regions in the model are predominantly concentrated within the amorphous phase. The phase dislocation entanglement under stress will improve the plasticity of the amorphous state. This work also discusses the deformation mechanism of nanocrystalline amorphous alloys at the atomic level.

2D X-ray diffraction method for evaluating the local crystallization of Fe-based amorphous alloy ribbon induced by ultrashort pulsed laser local heating

Fe-based amorphous alloys, which exhibit excellent soft magnetic properties, are difficult to machine, owing to their high strength, toughness, and hardness resulting from their unique structures. The authors proposed a novel blanking method that improves the machinability by crystallizing only the local regions involved in machining, thereby reducing the local strength and toughness. Because the micro-region mechanical properties of amorphous alloys vary greatly depending on the precipitated crystal species and volume fraction, it is necessary to nondestructively investigate the type of microstructure achieved by local heat treatment to determine the appropriate blanking conditions. However, an appropriate method for investigating crystals precipitated locally in an amorphous matrix is yet to be established. In this study, we used the 2D X-ray diffraction method to investigate the local crystallization of an Fe-based amorphous alloy ribbon after local heat treatment using an ultrashort pulsed laser. Furthermore, the 2D method was used to investigate the residual stresses in the fully crystallized amorphous alloy ribbons, and the results were compared using the sin2(ψ) method. The 2D method detected the slightly precipitated crystals in a local area with a radius of about 40 µm in the amorphous matrix. The integrated intensity of the diffraction peaks can be used to predict the internal structure after local heat treatment. Furthermore, the 2D method could measure residual stress with smaller error than the sin2(ψ) method. The core-shell crystals precipitated by heat treatment exhibited a compressive residual stress of −82 MPa to −67 MPa in the core Fe3B crystals and tensile residual stress of 39–60 MPa in the shell α-Fe crystals, approximately. The residual stress values of the precipitated crystals depended on the direction of rotation of the quenching roll used in the production of the amorphous alloy ribbons.

Effect of Minority Alloying Elements Zn and Zr on the Mechanical Properties of Amorphous Alloys АlCuMg(Zn) and AlCuMg(Zr) and their Nanocrystalline Analogues

Effect of Minority Alloying Elements Zn and Zr on the Mechanical Properties of Amorphous Alloys АlCuMg(Zn) and AlCuMg(Zr) and their Nanocrystalline Analogues

Formation ability, thermal stability, and mechanical properties of the Zr50Cu34Al8Ag8 amorphous alloys prepared by different mold materials

In the present study, Zr50Cu34Al8Ag8 amorphous alloy rods with a diameter of 3 mm were prepared and the influence of the cooling capacity on the properties of cast samples was analyzed. To this end, three mold materials, including heat-resistant steel, copper, and high purity graphite were utilized. Then the amorphous structure, glass-forming ability, and thermal stability of the cast alloy were investigated using an X-ray diffractometer and differential scanning calorimeter. A universal testing machine was applied to investigate the mechanical properties of amorphous alloys with different mold materials. The fracture characteristics of the amorphous alloy were analyzed by scanning electron microscope, and the microstructures were analyzed using a high-resolution transmission electron microscope. The experimental results showed that among the studied cases, the highest glass-forming ability was achieved from the copper mold. Moreover, the glass transition and crystallization activation energies of the amorphous alloy obtained by suction casting of high-purity graphite mold were the largest, which were 525.8 kJ/mol and 334.0 kJ/mol, respectively, reflecting good thermal stability. Meanwhile, the performed analyses revealed that the fracture strength of the amorphous alloy and the corresponding strain were 1888.2 MPa and 3.55%, respectively, indicating that the cast sample has good mechanical properties. With the decrease of the cooling rate, the content of free volume in the amorphous alloy of high-purity graphite mold suction casting decreased, and the ordered structure was generated, which was the main reason for its high thermal stability and plastic deformation ability.

Interface dominated deformation transition from inhomogeneous to apparent homogeneous mode in amorphous/amorphous nanolaminates

• A length-scale-dependent mechanical properties were observed in the A/ANLs. • The hardness of A/ANLs was closely related with their deformation mode. • The deformation mode of A/ANLs was determined by the interface. The amorphous/amorphous nanolaminates (A/ANLs) have aroused great attentions owing to their tunable structure and enhanced mechanical properties. However, the plastic deformation mechanism of A/ANLs have yet been clarified. Here, we systematically examined the mechanical properties and deformation behavior of series of NiNb/ZrCuNiAl A/ANLs via nanoindentaion test. It was found that both the amount and morphology of amorphous/amorphous interface (A/AIs) played crucial roles in the plastic deformation of A/ANLs. Less and straighter A/AIs facilitated multiple shear banding deformation, of which the hardness increased with decreasing layer thickness, as the A/AIs hindered the propagation of shear bands (SBs). Whilst, more and wavier A/AIs promoted homogeneous deformation, of which the hardness stayed at a much lower value and was relatively irrelevant with the layer thickness, for the promoted activation of shear transformation zones by A/AIs. Our results provide guidance for modifying the mechanical properties of amorphous alloys with interface engineering design.

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.

Microstructure and mechanical properties of Zr55Cu30Al10Ni5 amorphous alloy with high-energy states produced by strip casting

In this work, the twin-roll strip-casting technique was used to produce high-energy state Zr55Cu30Al10Ni5 (at%) amorphous alloy sheets. The effect of the temperatures of the alloy melt on their microstructure during production process was studied. The deformation mechanism of the fabricated pure amorphous alloy sheets, in addition to the effects of the formed crystalline particles in them, on their ductility and strength were investigated through mechanical property tests and in situ observations of their microdeformation and microfracture processes. The results indicated that the formation and growth of crystalline particles in amorphous alloy sheets can be inhibited by increasing the melting and casting temperatures of the alloy melt. The fabricated high-energy amorphous alloy sheets exhibit significant plasticity in compression at room temperature, which was achieved through the sequential formation and cross growth of multiple shear bands. Moreover, the appropriate crystalline particles in the alloys could impede the linear propagation of the shear bands in the initial stage of compression deformation, which makes the alloys exhibit a certain level of work-hardening. However, with the increase in deformation, these crystalline particles became the source of the cracks in the alloys and accelerated their fracturing. Overall, this research provides an effective idea for regulating the microstructure and mechanical properties of amorphous alloys. In addition, it offers a significant guide for the industrial production of large amorphous alloy sheets.

Accelerated rejuvenation in metallic glasses subjected to elastostatic compression along alternating directions

The influence of static stress and alternating loading direction on the potential energy and mechanical properties of amorphous alloys is investigated using molecular dynamics simulations. The model glass is represented via a binary mixture which is first slowly annealed well below the glass transition temperature and then subjected to elastostatic loading either along a single direction or along two and three alternating directions. We find that at sufficiently large values of the static stress, the binary glass becomes rejuvenated via collective, irreversible rearrangements of atoms. Upon including additional orientation of the static stress in the loading protocol, the rejuvenation effect is amplified and the typical size of clusters of atoms with large nonaffine displacements increases. As a result of prolonged mechanical loading, the elastic modulus and the peak value of the stress overshoot during startup continuous compression become significantly reduced, especially for loading protocols with alternating stress orientation. These findings are important for the design of novel processing methods to improve mechanical properties of metallic glasses.

The effect of thermal history on the atomic structure and mechanical properties of amorphous alloys

The influence of thermal processing on the potential energy, atomic structure, and mechanical properties of metallic glasses is examined using molecular dynamics simulations. We study the three-dimensional binary mixture, which was first relaxed near the glass transition temperature and zero pressure, and then rapidly cooled deep into the glass phase. It was found that glasses annealed at higher temperatures are relocated to higher energy states and their average glass structure remains more disordered, as reflected in the height of the first two peaks in the pair distribution function. The results of mechanical testing demonstrate that both the shear modulus and yielding peak increase significantly when the annealing temperature approaches Tg from above. Moreover, the shear modulus becomes a strong function of strain rate only for glasses relaxed at temperatures sufficiently higher than the glass transition temperature. Based on the spatial distribution of nonaffine displacements, we show that the deformation mode changes from brittle to ductile upon increasing annealing temperature. These results can be useful for the design and optimization of the fabrication processes of bulk glassy alloys with improved plasticity.

Unraveling the non-monotonic ageing of metallic glasses in the metastability-temperature space

Ageing behaviors of metallic glasses are investigated by atomistic modeling in a broad range of processing histories and thermal conditions. By employing an enhanced data-mining analysis, a non-monotonic ageing phenomenon is resolved with high precision. It is observed that there exists a non-linear correlation between the system’s metastability and the critical temperature where maximum ageing rate occurs. In further conjunction with the recently developed energy landscape theory to circumvent the time-scale limitations of molecular dynamics, the ageing rate contours over ten orders of magnitude are mapped out in the metastability-temperature space. Such map enables a natural explanation to the experimentally observed shift of exothermic signal, which cannot be provided by existing models. Implications of the present study for understanding the mechanical properties of amorphous alloys are also discussed.

Mapping the Non-Monotonic Ageing of Metallic Glasses in the Metastability-Temperature Space

Ageing behaviors of metallic glasses are investigated by atomistic modeling in a broad range of processing histories and thermal conditions. By employing an enhanced data-mining analysis, a non-monotonic ageing phenomenon is resolved with high precision. It is observed that there exists a non-linear correlation between the system's metastability and the critical temperature where maximum ageing rate occurs. In further conjunction with the recently developed energy landscape theory to circumvent the time-scale limitations of molecular dynamics, the ageing rate contours over ten orders of magnitude are mapped out in the metastability-temperature space. Such map enables a natural explanation to the experimentally observed shift of exothermic signal, which cannot be provided by existing models. Implications of the present study for understanding the mechanical properties of amorphous alloys are also discussed.

Mechanical behavior of amorphous alloys

The mechanical properties of amorphous alloys have proven both scientifically unique and of potential practical interest, although the underlying deformation physics of these materials remain less firmly established as compared with crystalline alloys. In this article, we review recent advances in understanding the mechanical behavior of metallic glasses, with particular emphasis on the deformation and fracture mechanisms. Atomistic as well as continuum modeling and experimental work on elasticity, plastic flow and localization, fracture and fatigue are all discussed, and theoretical developments are connected, where possible, with macroscopic experimental responses. The role of glass structure on mechanical properties, and conversely, the effect of deformation upon glass structure, are also described. The mechanical properties of metallic glass-derivative materials – including in situ and ex situ composites, foams and nanocrystal-reinforced glasses – are reviewed as well. Finally, we identify a number of important unresolved issues for the field.

Effect of a controlled volume fraction of dendritic phases on tensile and compressive ductility in La-based metallic glass matrix composites

A systematic study has been carried out to identify the effect of crystalline second phase reinforcements on the mechanical properties of amorphous alloys based on the composition La 86− y Al 14(Cu, Ni) y ( y=1–24). By varying the composition in a controlled manner, composites with a tailorable fraction of in situ dendritic reinforcements were produced. Tension, compression and impact tests showed considerably improved mechanical properties with a large amount of plasticity when the reinforcement volume fraction exceeded a critical value near 40%, and the tension/compression asymmetry associated with glass plasticity is reduced as the volume fraction of crystalline reinforcements rises.

Wear resistance of amorphous alloys and related materials

Amorphous alloys, and the partially or fully crystallised materials derived from them, can have properties attractive for a diverse range of applications. In some cases, their wear resistance can be of primary concern, in others, it is an important secondary property. The distinctive mechanical properties of amorphous alloys make their wear resistance of fundamental interest also. This review focuses on the influence of a variety of factors in wear testing, on the mechanisms of wear, on the characteristics of different categories of amorphous alloy, and on the effects of partial or complete crystallisation. It is shown that amorphous alloys can have very good resistance to sliding and abrasive wear. The wear resistance of related quasicrystalline phases is also considered.

On extending dislocation notions to the amorphous state of solids

Anomalies (minima of σ fp) are discovered in composition dependencies of the critical stress σ fp for catastrophic shear of the Fe 100− x B x , Fe 80− x Ni x B 20 and Fe 85− x Co x B 15 amorphous alloys. These minima correspond to the eutectic ( x=17) in the Fe–B system, to x=40 in the Fe–Ni–B system and to x=40 and 21 in the Fe–Co–B system. Considering mobile dislocations in amorphous alloys located at boundaries between nanoclusters makes it possible to explain and to predict anomalous (non-monotonous) composition dependencies of mechanical properties of amorphous alloys.

Excess free volume and mechanical properties of amorphous alloys

Characteristics of the excess free volume in amorphous alloys quenched from a melt are investigated and analyzed. It is established by small-angle x-ray scattering that the application of intense hydrostatic pressure causes this volume to decrease. This decrease leads to an enhancement of a number of characteristics of the mechanical properties of amorphous alloys.

Effect of film composition and microstructure on microindentation response in amorphous alloy coatings

Amorphous alloy coatings were deposited onto Ni substrates by decomposing metal carbonyls [Ni(CO)4 and Fe(CO)5] and metalloid hydrides (PH3 and B2H6) by chemical vapor deposition in an rf plasma. The chemical composition of these films was determined using Auger electron spectroscopy and the hybridization (i.e., bonding character) of the metalloids (phosphorus, boron, and carbon) has been evaluated by using Auger line‐shape analysis. The amorphous/crystalline nature of these alloys was evaluated using x‐ray and electron diffraction techniques. The microindentation load‐depth response of these films was measured with an ultralow‐load hardness tester capable of testing at loads less than 10 g and at penetration depths less than 1 μm. The results of these measurements are discussed in the light of theories which attempt to relate mechanical properties of amorphous alloys to the bonding character of the outer electrons of the component elements.

Transformation studies and mechanical properties of melt-quenched amorphous titanium-silicon alloys

The formation, stability and decomposition characteristics of the amorphous phase in binary titanium-silicon alloys rapidly quenched from the molten state have been investigated. Electron microscopy and diffraction coupled with X-ray diffraction techniques suggested that the amorphous phase could be obtained in alloys containing 15 to 20 at% silicon. The transformation of the amorphous phase to the equilibrium phases took place in two stages. A metastable b c c titanium solid solution, containing silicon in excess of the equilibrium value, formed initially, followed by the precipitation of the Ti5Si3 intermetallic compound. Microstructural features at various stages of decomposition have been described and interpreted in terms of the constitution of the alloys. Mechanical properties of the amorphous alloys have also been investigated.