Cu-based Bulk Metallic Glasses Research Articles

Substantially enhanced plasticity of bulk metallic glasses by densifying local atomic packing

Introducing regions of looser atomic packing in bulk metallic glasses (BMGs) was reported to facilitate plastic deformation, rendering BMGs more ductile at room temperature. Here, we present a different alloy design approach, namely, doping the nonmetallic elements to form densely packed motifs. The enhanced structural fluctuations in Ti-, Zr- and Cu-based BMG systems leads to improved strength and renders these solutes’ atomic neighborhoods more prone to plastic deformation at an increased critical stress. As a result, we simultaneously increased the compressive plasticity (from ∼8% to unfractured), strength (from ∼1725 to 1925 MPa) and toughness (from 87 ± 10 to 165 ± 15 MPa√m), as exemplarily demonstrated for the Zr20Cu20Hf20Ti20Ni20 BMG. Our study advances the understanding of the atomic-scale origin of structure-property relationships in amorphous solids and provides a new strategy for ductilizing BMG without sacrificing strength.

Dual-cluster model of Ti–Cu binary eutectic and composition interpretation of relevant amorphous alloys

Glass formation is usually related to deep eutectic points. The present work addresses the composition interpretation of eutectic Ti57Cu43 and relevant bulk metallic glasses (BMGs) by introducing the “dual-cluster” model. In this model, the eutectic liquid structure is presumably composed of two chemical units derived from relevant eutectic phases, each corresponding to a stable liquid satisfying a general cluster formula for ideal metallic glasses [cluster](glue atom)1or3 in terms of the cluster-plus-glue-atom model. Detailed procedures are introduced to apply this model in interpreting the eutectics, based on which eutectic Ti57Cu43 is interpreted as dual-cluster formulas of 2{[Ti–Cu6Ti8]Cu3} + [Ti–Cu5Ti9]Ti3 and 2{[Ti–Cu6Ti8]Cu2Ti} + [Ti–Cu5Ti9]Cu2Ti, where the two clusters [Ti–Cu6Ti8] and [Ti–Cu5Ti9] are, respectively, derived from eutectic phases TiCu and Ti2Cu. Two interpretations are equivalent, and one of the involved chemical units [Ti–Cu6Ti8]Cu3 = Ti50Cu50 is a basic unit for multicomponent Ti–Cu-based BMGs; typical BMGs are formed by replacing the atoms in the basic unit with alloying ones.

Effect of Al addition on properties of Cu45Zr45.5Ti9.5 bulk metallic glass

The thermal, mechanical and corrosive properties of (Cu45Zr45.5Ti9.5)100-xAlx (x = 0–0.25 at%) glass forming alloys were systematically studied. The thermal measurements show that Al microalloying leads to increase of glass transition temperature but decrease of supercooled liquid region. The glass transition activation energy slightly increases and then decreases with increasing Al content. The room-temperature compression tests demonstrate that all studied Cu-based bulk metallic glasses (BMGs) exhibit work-hardening behavior, but the work-hardening capacity depends on Al content. In addition, yield strength, fracture strength and fracture strain are drastically increased by Al addition. The largest plasticity of (Cu45Zr45.5Ti9.5)99.8Al0.2 BMG is 6 times larger than that of the Al-free Cu-based BMG. Moreover, the electrochemical measurements indicate that the Al minor addition cause the decrease of both corrosion potential and corrosion current density. The corrosion behavior gradually transforms from the pitting corrosion to the self-passivization with increasing Al content. The local heterogeneity of Al element is thought to be the reason for the performance change of the studied Cu-based BMGs. The present results would provide a new insight into the mechanism for the microalloying effect on the properties of the metallic glasses.

Serrated Behaviors and Plasticity of Nb-Alloyed Cu-Based Bulk Metallic Glasses

This paper is to disclose the plastic deformation mechanism of 3 Nb-alloyed bulk metallic glasses and composites via the analysis of serration dynamics. The as-cast alloys with 1.0 at% and 2.0 at% of Nb element display the large time window of serrated events, implying that the serrated behavior can dynamically retain in a long-time scale and thus the alloys are endowed the largest compressive plasticity. The statistic results suggest that the serrated flow of both alloys with 1.0 at% and 2.0 at% Nb element achieves the self-organized critical state. The normal probability plots were utilized to further evaluate serrated dynamics and demonstrate that large deviations from the mean value of stress drops facilitate the self-organized critical state of serrations. This work suggests that large plastic bulk metallic glasses and composites are characterized by non-normal probability of serration statistics during plastic deformation.

Design of Cu-Zr-Al and Cu-Zr-Al-Sn bulk amorphous alloys with high glass-forming ability

The thermodynamic driving force is used to obtain the initial mixing ratio of binary eutectics to design Cu-based bulk metallic glasses. By adjusting approximately 5% proportionality coefficients from the primary mixing ratios of eutectic units, we directly locate amorphous compositions with critical casting diameter of 5 mm (Cu47.5Zr45.1Al7.4) and 7 mm (Cu47.3Zr45.8Al6.4Sn0.5) in Cu-Zr-Al and Cu-Zr-Al-Sn systems, respectively. Using the Cu-Zr-Al alloys as an example, the improvement of glass-forming ability (GFA) is systematically analyzed based on thermodynamics and atomic-scale structure. A relatively lower driving force for crystallization and larger populations of Cu-centered full icosahedra with the large tendency to form MROs jointly contribute to the stability of liquid. With regard to topology, the closer local atomic size ratio compared with the ideal value for icosahedral packing around the Cu atom may be the dominant factor for the higher number of Cu-centered full icosahedra and enhanced GFA.

Effect of Fe-C alloy additions on properties of Cu-Zr-Ti metallic glasses

The effect of Fe-C alloy additions on thermal, mechanical and corrosive properties of (Cu50Zr40Ti10)1-x(Fe-C)x (x = 0–2.20 at%) alloys were systematically investigated. The results show that the Fe and C additions can enhance glass transition temperature Tg and onset crystallization temperature Tx, but narrow supercooled liquid region ΔTx. Work-hardening can be clearly observed for the Cu-based bulk metallic glasses (BMGs) containing Fe and C elements. The yield strength (σy), fracture strength (σf) and plastic strain (εp) are drastically increased by Fe-C alloy additions. The corrosion potential Ec increases and the corrosion current density ic decreases with increasing Fe and C contents. The studied Cu-based BMGs exhibit unique and novel anodic polarization behavior characterized by current platforms plus current serrations. The current serrations are much larger for the Cu-based BMGs with 0 ≤ x ≤ 1.32 at% than for those with 1.76 ≤ x ≤ 2.20 at%. The corrosion surface images are changed from the pits to the passive films by Fe-C alloy additions. The corrosion behavior gradually transforms from the pitting corrosion to the self-passivization with increasing Fe and C contents. The corresponding mechanisms are also discussed.

Three-dimensional structure and formation mechanisms of Y2O3 hollow-precipitates in a Cu-based metallic glass

Recently, the high ductility of Cu-based bulk metallic glasses (BMGs) has been directly linked to the presence of Y2O3 precipitates, and surrounding crystallized areas. Nevertheless, the formation of the precipitates remains to be defined. In this work, the structure of Y2O3 precipitates and crystallized zones of the BMG are investigated at the nanoscale in three-dimensions, shining light on their spatial distribution and their origin. Two kinds of precipitates were observed: small solid ones and large hollow ones. The mechanism proposed to explain the formation of hollow-precipitates is based on the Kirkendall effect. A model was implemented to assess the feasibility of this mechanism with the experimental results. Moreover, our results suggest that micro and nano-crystallized areas within the BMG are induced by the presence of yttria precipitates, with a correspondence between the size of the precipitate and the size of the crystallized areas.

Crystallization Behavior and Mechanical Properties of Cu-based Bulk Metallic Glass Composites

This work highlights the relationship between the preparation, crystallization behavior, microstructures, and mechanical properties of Cu-based bulk metallic glasses (BMGs) and their composites (BMGCs). (Cu47Zr45Al8)97.5Y1.5Nb in-situ BMGCs were prepared using isothermal annealing, and the experimental results indicate tunable mechanical properties of the alloys by processing parameter manipulation. The crystallinity of (Cu47Zr45Al8)97.5Y1.5Nb BMGCs increases with extended annealing temperature and time, while their phase transition with rising temperature follows Am (amorphous state) → Am + Cu10Zr7 →Am + Cu10Zr7 + AlCu2Zr + Al2Zr. Precipitation strengthening during annealing above 720 K (447 oC) can enhance the alloy microhardness remarkably and achieve an optimum of 712 HV by annealing at 800 K (527 oC) for 60 min. TEM results show that Cu10Zr7 with sizes of 12~15 nm precipitates out upon crystallization and thereby accounts for the superior compressive property. The alloy exhibits a fracture strength up to 2080 MPa after annealing at 680 K (407 oC) for 30 min. Morphological observation of the fracture surface reveals a transition of fracture characteristics from the typical amorphous ductile manner to a brittle manner with further annealing. The investigation provides novel thoughts of BMGs processing for further performance improvement.

Effects of microadditions on glass transition and hardness of Cu-based bulk metallic glasses

In this paper, glass-forming ability, viscosity, fragility and microhardness of three Cu-based bulk metallic glasses are evaluated by differential scanning calorimetry, thermomechanical analysis and hardness testing. The results suggest that Y element can effectively affect the packing state and properties of Cu-based bulk metallic glasses. The variation of glass-forming ability, viscosity, fragility index and hardness indicates that alloying with low quantity of additions can remarkably change the characteristic temperatures during glass transition stage but cannot cause an apparent modification in the solidification/melting stage.

Hardness and Modulus of Cu-based Bulk Metallic Glasses via Nanoindentation

Abstract The hardness and Young'modulus for two Cu-based bulk metallic glasses, Cu59Zr36Ti5 and Cu61Zr34Ti5, has been studied by nanoindentation in three different ways, including load rate control mode, load control mode, and cycles load control mode. Young's modulus of the specimen shows the dependence on loading rate when the loading rate is no more than 5 mN/s. The Young's modulus of both Cu59Zr36Ti5 and Cu61Zr34Ti5 decreases with the increasing of holding load and loading rate. But neither loading rate nor holding load has significant influence on hardness. Cyclic loading leads to slight hardening for Cu59Zr36Ti5, while Cu61Zr34Ti5 doesn't show such results. What's more, Cu61Zr34Ti5 exhibits obviously higher hardness and modulus than Cu59Zr36Ti5.

The introduction of highly dense shear bands and their effect on plastic deformation in Zr and Cu-based bulk metallic glasses

The plastic deformation of the Zr64.13Cu15.75Ni10.12Al10 and Cu60Zr30Ti10 bulk metallic glasses (BMGs) with arc-shaped edges were performed by compression. Highly dense shear bands with an average spacing of 520nm are uniformly distributed in a large area in Zr64.13Cu15.75Ni10.12Al10 BMG, and the shear band spacing can be reduced to a minimum value of about 110nm. In the region adjacent to the dense shear band zone in Zr64.13Cu15.75Ni10.12Al10 BMG, the shear band spacing increases linearly. Similarly, highly dense shear bands were also introduced into Cu60Zr30Ti10 BMG. When the width of stress concentration zone is of the order of plastic zone size ahead of crack tip, the internal and external stress limitations can lead to the formation of a large number of uniformly-distributed shear bands. In addition, the pre-existing dense shear bands can lead to a non-localized plastic deformation manner for deformed Zr64.13Cu15.75Ni10.12Al10 BMG.

Strong, ductile, and thermally stable Cu-based metal-intermetallic nanostructured composites

Bulk metallic glasses (BMGs) and nanocrystalline metals (NMs) have been extensively investigated due to their superior strengths and elastic limits. Despite these excellent mechanical properties, low ductility at room temperature and poor microstructural stability at elevated temperatures often limit their practical applications. Thus, there is a need for a metallic material system that can overcome these performance limits of BMGs and NMs. Here, we present novel Cu-based metal-intermetallic nanostructured composites (MINCs), which exhibit high ultimate compressive strengths (over 2 GPa), high compressive failure strain (over 20%), and superior microstructural stability even at temperatures above the glass transition temperature of Cu-based BMGs. Rapid solidification produces a unique ultra-fine microstructure that contains a large volume fraction of Cu5Zr superlattice intermetallic compound; this contributes to the high strength and superior thermal stability. Mechanical and microstructural characterizations reveal that substantial accumulation of phase boundary sliding at metal/intermetallic interfaces accounts for the extensive ductility observed.

Effects of aspect ratio and loading rate on room-temperature mechanical properties of Cu-based bulk metallic glasses

Room-temperature mechanical properties of Cu50Zr40Ti10–xNix (0≤x≤4, mole fraction, %) bulk metallic glasses (BMG) with aspect ratios in the range of 1:1–2.5:1 and loading rates in the range of 1×10−5–1×10−2 s−1 were systematically investigated by room-temperature uniaxial compression test. In the condition of an aspect ratio of 1:1, the superplasticity can be clearly observed for Cu50Zr40Ti10 BMG when the loading rate is 1×10−4 s−1, while for Cu50Zr40Ti10–xNix (x=1–3, mole fraction, %) BMGs when the loading rate is 1×10−2 s−1. The plastic strain (ɛp), yielding strength (σy) and fracture strength (σf) of the studied Cu-based BMGs significantly depend on the aspect ratio and the loading rate. In addition, the σy of the studied Cu-based BMGs with an aspect ratio of 1:1 is close to the σf of those with the other aspect ratios when the loading rate is 1×10−2 s−1. The mechanism for the mechanical response to the loading rate and the aspect ratio was also discussed.

Understanding of micro-alloying on plasticity in Cu46Zr47−xAl7Dyx (0≤ x ≤ 8) bulk metallic glasses under compression: Based on mechanical relaxations and theoretical analysis

Lacking of plasticity at ambient temperature severely hinders the wide applications of bulk metallic glasses, and a significant challenge is to improve the plasticity. Based on the metallurgical physics, micro-alloying can be applied to adjust metallic glasses plasticity. In the current work, dynamic mechanical relaxation of Cu46Zr47−xAl7Dyx (0 ≤ x ≤ 8) bulk metallic glasses has been investigated experimentally by dynamic mechanical analysis. Compressive tests have been performed to investigate mechanical properties of the Cu-based bulk metallic glasses at both ambient as well as cryogenic temperatures. The results indicated that by modifying the chemical composition, plastic deformation and dynamic mechanical relaxation processes are changed. The influence of Dysprosium (Dy) on plastic deformation is possibly related to the Johari-Goldstein (JG) relaxation in the metallic glasses. A kinetic model which may be predict the mechanical relaxation behavior and atomic mobility of the metallic glasses. In addition, experimental analyses show that thermal properties can be affected by the Dy addition of the Cu-based bulk metallic glasses. Our investigations demonstrated that micro-alloying of Dy could play an important role to influence the Cu46Zr47−xAl7Dyx bulk metallic glasses plasticity. In order to explain this behavior, the quasi-point defects theory was used to describe the microstructural heterogeneity. We postulate that the compressive plasticity is directly associated with local heterogeneity and relaxation modes for metallic glasses.

Ultraviolet light irradiation on pitting corrosion of Cu-based bulk metallic glasses

We report the observation that UV irradiation substantially improves pitting corrosion resistance of Cu-based bulk metallic glasses. Specifically, two Cu-based bulk metallic glasses in this study showed more stable passive films under UV irradiation than under irradiation-free condition when polarized in 3.5 wt.% NaCl aqueous solution. This finding indicates that Cu-based bulk metallic glasses are promising to serve in high UV irradiation and corrosive environments.

Microalloying and microstructures of Cu-based bulk metallic glasses & composites and relevant mechanical properties

To improve the poor plasticity of bulk metallic glasses, this work reports the microalloying of a bulk metallic glass to tailor the microstructures and to enhance its plasticity. The selection of alloying elements, Hf and Mo which are soluble in Ti, is determined by binary phase diagrams. The X-ray diffraction and microstructural analysis demonstrate that the microstructural evolution of as-cast alloys is accompanied with the addition of alloying elements. The glass-forming ability of as-cast alloys increases with the addition of Hf and Mo elements, respectively. The yield strength and plasticity of both as-cast alloys are affected with the quantity of alloying elements. In addition, the intrinsic nature of alloying elements and the interaction among the alloying elements and base compositions affect the hardness of as-cast alloys. Summarily, addition of soluble alloying elements in a component of base composition can enhance the plasticity of bulk metallic glasses.

Microstructure evolution and mechanical properties of Nb-alloyed Cu-based bulk metallic glasses and composites

Abstract This paper reports the microstructure evolution of Cu50.2 Zr40.8Ti9−xNbx (x = 0.5, 1.0, and 2.0 at.%) bulk metallic glass and bulk metallic glass composites accompanied with the addition of Nb and the corresponding mechanical properties. The X-ray diffraction and characterization of microstructures demonstrate that the microstructures of as-cast alloys undergo a composite-amorphous evolution. DSC analysis indicates that the glass-forming ability of as-cast alloys increases with addition of Nb. The microstructure evolution can be contributed to the combination of the stabilization of Nb on precipitated crystalline phases and cooling time. 1.0 at.% Nb-alloyed sample has the best plasticity (15.1%) and the highest fracture strength (2205 MPa) among three as-cast alloys. This work suggests that the uniformly dispersed tiny crystalline phases in glassy matrix can enhance the plasticity of bulk metallic glasses.

New insight on glass-forming ability and designing Cu-based bulk metallic glasses: The solidification range perspective

In this paper, a new equation was rationally generalized from the reduced glass transition temperature. This equation indicates that solidification range can be used for describing glass-forming ability, which can be calculated with the aid of computational thermodynamic approach. Based on this scenario, several new Cu-based bulk metallic glasses in the ternary Cu–Zr–Ti alloy system were discovered. The as-cast samples were characterized by X-ray diffraction and transmission electronic microscopy. The results indicate that as-cast samples have monolithic amorphous nature. Thermal analysis validates that the smaller solidification range is closely related to the higher glass-forming ability, which is contributed to the effect of solidification time on the formation of bulk metallic glasses. This work also suggests that solidus can influence glass formation.

Influence of Minor Addition of In on Corrosion Resistance of Cu-Based Bulk Metallic Glasses in 3.5% NaCl Solution

Abstract The corrosion resistances of bulk metallic glasses (BMGs) Cu 55− x Zr 37 Ti 8 In x ( x =0∼5, at%) and Cu 61− x Zr 34 Ti 5 In x ( x =0∼3, at%) were investigated in 3.5 wt% NaCl aqueous solution. The electrochemical potentiodynamic polarization curves demonstrate that the addition of indium to copper-based BMGs can significantly enhance the corrosion potential and reduce the corrosion current density, i.e. greatly improves the corrosion resistance. And the value of I corr for copper-based BMGs added with indium is lower than those without indium addition, by roughly one order of magnitude. The moderate replacement of copper by indium improves the corrosion resistance further. While the excessive addition of indium reduces the corrosion resistance, resulting from the lack of Zr-rich protective surface film.

Nanoindentation Mechanical Properties of Indium-Alloyed Cu-Based Bulk Metallic Glasses

In this paper, two Indium-alloyed Cu-based bulk metallic glasses, Cu54Zr37Ti8In1 and Cu50Zr37Ti8In5, have been evaluated with nanoindentation testing. Both bulk metallic glasses have homogenous nature in structure. Both hardness and Young’s modulus of bulk metallic glasses do not show a loading rate-dependent. Addition of In decreases hardness and Young’s modulus, but increases creep-resistance of bulk metallic glasses. Indentation creep of two bulk metallic glasses has also been investigated. The displacement-time curves of creep processes were described with generalized Kelvin model. The creep displacement, compliance spectrum, and retardation spectrum for each bulk metallic glass were discussed comparatively. The results showed that Cu50Zr37Ti8In5 has better creep-resistance at room temperature and a more relaxed state.