Plastic Flow of a Cu50Zr45Ti5 Bulk Metallic Glass Composite

By modifying the cooling rate, a Cu50Zr45Ti5 alloy with various structures was developed. A fully glassy rod and specimens with different sizes and volume fractions ofnanocrystals were produced. The relationship between the structure and mechanical properties of the Cu50Zr45Ti5 alloy was investigated. The different structures result in a transition of the deformation mechanism from being dominated by shear banding to being governed by dislocation action accompanied by shear band formation. These different plastic deformation mechanisms were discussed in the framework of self-organized critical behavior.     

Ti50Cu25Ni20Sn5 bulk metallic glass fabricated by powder consolidation

A bulk metallic glass of Ti₅₀Cu₂₅Ni₂₀Sn₅ nominal composition was produced via a powder metallurgical route, namely the preparation of glassy powders by mechanical alloying followed by their consolidation by spark-plasma sintering. Samples were characterized with respect to their structure and thermal properties before and after sintering. A bulk glassy sample, having nearly full density and containing only a small fraction of the intermetallic NiTi₂ phase, could be obtained after careful selection of sintering parameters.     

Microstructural evolution during annealing and rolling Zr52.5Cu17.9Ni14.6Al10Ti5 bulk metallic glass

The microstructural evolution of the Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ bulk metallic glass during annealing and rolling deformation was studied. After annealing at 680 K for 0.5 h, phase separation is observed, and nanocrystallization is further induced by the subsequent rolling deformation. Increasing annealing time to 1.5 h leads to the formation of both nanocrystals and large-size particles of the Zr–Cu fcc phase. After rolling, the volume fraction of nanocrystals increases slightly while the Zr–Cu particles disappear. The presence of phase separation and nanocrystals during annealing reduce the thermal stability of the glass and accelerate the subsequent crystallization driven by rolling. During rolling the two annealed specimens exhibit the good ductility.     

In vitro biocompatibility assessment of Ti40Cu38Zr10Pd12 bulk metallic glass

The use of biocompatible materials has attained an increasing importance for tissue regeneration and transplantation. The excellent mechanical and corrosion properties of Ti₄₀Cu₃₈Zr₁₀Pd₁₂ bulk metallic glass (BMG) turn it into a potential candidate for its use in orthopaedic implants. Before being considered as a biomaterial, some biological parameters must be taken into account. In this study, mouse preosteoblasts were cultured in the presence or absence of the alloy at different times (24 h, 7 and 21 days) and no differences in cell viability were detected. Moreover, cells were able to adhere to the alloy surface by establishing focal contacts, and displayed a flattened polygonal morphology. After 14 days in culture, differentiation into osteoblasts was observed. Besides, the amount of Cu ions released and their potential toxic effects were analyzed, showing that the amount of Cu released did not increase cell death. Finally, the low levels of inflammatory cytokines secreted by THP-1 differentiated macrophages exposed to the alloy suggest the absence of an immunogenic response to the alloy. In conclusion, in vitro studies indicate that the Ti₄₀Cu₃₈Zr₁₀Pd₁₂ BMG could be considered as a biomaterial to be used in orthopaedic implants.     

The evolution of Cu-rich domains in the Cu60Zr30Ti10 metallic glass by ASAXS

The structure of the melt-spun Cu₆₀Zr₃₀Ti₁₀ metallic glass is investigated by anomalous small angle X-ray scattering (ASAXS). It is confirmed that the compositional segregation in the diameter range of 30–50 nm exists in the as-quenched state. ASAXS results have convincingly shown the aggregation of Cu atoms and the formation of Cu-rich domains in the amorphous matrix. The Cu-rich domains grow slightly with low growth rate below the glass transition temperature, while the sizes of these domains drastically increase with high growth rate in the supercooled liquid temperature region. The Cu-rich domains are presumed to be associated with nucleation for the primary crystallization process.     

The structure and mechanical properties of bulk Zr50Ti16.5Cu15Ni18.5 metallic glasses

The structure and mechanical properties of bulk Zr₅₀Ti_16.5Cu₁₅Ni_18.5 metallic glasses were studied by X-ray diffraction, scanning and transmission electron microscopy and by measurements of mechanical properties. The transition from heterogeneous to homogeneous deformation was found to occur at 575 K. The crystallization was found to begin in the testing part of the sample earlier than in the part placed in a holder during the mechanical testing. The crystallization leads to the formation of the quasicrystalline phase with a ₀ = 2.54 Å, hexagonal phase ZrTi(Ni,Cu) and hexagonal phase (Zr₆CoAl₂ type). The difference of the structure in different parts of the sample has been observed and analyzed. The deformation does not effect on the crystallization processes occurring during the tensile testing at this temperature and the crystallization proceeds owing to the self-heating of the samples during the phase transition. The correlation between mechanical properties, structure and fracture surfaces is discussed.     

The effect of decomposition on crystallization in Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass

The decomposition as well as its effects on the crystallization of the bulk metallic glass (MG) Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 has been investigated using transmission electron microscopy (TEM). It is found that the decomposition destabilizes the MG and makes the MG thermally less stable with respect to crystallization. The effects of the phase separation on the subsequent crystallization are discussed based on the microstructural characteristics of the MG.     

Compression behaviour and micro-structure evaluation of Zr57Nb5Cu15.4Ni12.6Al10 bulk metallic glass under high pressure

Compression behaviour and micro-structure evaluation of Zr₅₇Nb₅Cu_15.4Ni_12.6Al₁₀ bulk metallic glass is investigated at room temperature up to 32.8 GPa using in-situ high pressure energy dispersive X-ray diffraction with a synchrotron radiation source. The equation of state of the bulk metallic glass is − ΔV / V = 0.012P − 2.49 × 10^− 4P² − 9.5 × 10^− 7P³ + 5.02 × 10^− 8P⁴. The result shows that the nearest atom pair of the as-quenched bulk metallic glass corresponds to Zr–Zr correlations. And with pressure increasing, the nearest atom pair changes to a new one at 32.8 GPa.     

Diffusion bonding of Zr55Cu30Ni5Al10 bulk metallic glass to Cu with Al as transition layer

In this work we demonstrate the diffusion bonding of Zr₅₅Cu₃₀Ni₅Al₁₀ bulk metallic glass (BMG) to aluminum and copper alloy. The process parameters including temperature, pressure and time are investigated experimentally, and we obtain appropriate ones for accomplishing diffusion bonding of the BMG to aluminum alloy successfully. Then we present a two-step diffusion bonding process to bond the BMG to copper alloy by using aluminum alloy as transition layers, and achieve a five-layer bonded joint of BMG/Al/Cu/Al/BMG. The mechanical properties of the multilayer joint are examined. The hardness of the BMG in the joint is enhanced while the bending strength decreases significantly compared with the as-received BMG. Besides, the crystalline metals alleviate and block the extension of cracks in the BMG, which results in the joint fracturing in an explosion-proof glass manner, dissimilar to rupturing in a catastrophic manner that is always happened in the BMGs. Therefore, diffusion bonding of BMG to crystalline metals is a promising way to extend its application.     

Bending fatigue behavior of thin Zr61Ti2Cu25Al12 bulk metallic glass beams for compliant mechanisms application

In this work,bending fatigue behavior of thinner Zr61Ti2Cu25Al12 (ZT1) BMG beams with thicknesses of 500 μm and 100 μm were investigated with three-point bendin...     

Tribological properties of Ti40Zr25Ni8Cu9Be18 bulk metallic glasses under different conditions

The tribological behavior of Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈ bulk metallic glasses (BMGs) under dry sliding and deionized water, as well as in 30%, 60%, and 90% hydrogen peroxide solution, were investigated by a block-on-disc test. This study demonstrates that the environmental conditions significantly affect the tribological behavior of the BMGs. The friction coefficient was lowest under the dry sliding condition and highest under 60% hydrogen peroxide solution. The wear resistance of BMGs was highest under the dry sliding condition, and lowest under 30% hydrogen peroxide solution. Analysis of the worn surface revealed that the Ti-based BMGs exhibited inhomogeneous plastic deformation, abrasive wear, adhesive wear, micro-cutting, and peeling off during sliding. In addition, the wear mechanism may have changed with an alteration in the environment.     

Zr61Ti2Cu25Al12 metallic glass for potential use in dental implants: Biocompatibility assessment by in vitro cellular responses

In comparison with titanium and its alloys, Zr₆₁Ti₂Cu₂₅Al₁₂ (ZT1) bulk metallic glass (BMG) manifests a good combination of high strength, high fracture toughness and lower Young's modulus. To examine its biocompatibility required for potential use in dental implants, this BMG was used as a cell growth subtract for three types of cell lines, L929 fibroblasts, human umbilical vein endothelial cells (HUVEC), and osteoblast-like MG63 cells. For a comparison, these cell lines were in parallel cultured and grown also on commercially pure titanium (CP-Ti) and Ti6–Al4–V alloy (Ti64). Cellular responses on the three metals, including adhesion, morphology and viability, were characterized using the SEM visualization and CCK-8 assay. Furthermore, real-time RT-PCR was used to measure the activity of integrin β, alkaline phosphatase (ALP) and type I collagen (COL I) in adherent MG63 cells. As indicated, in all cases of three cell lines, no significant differences in the initial attachment and viability/proliferation were found between ZT1, CP-Ti, and Ti64 until 5 d of incubation period. It means that the biocompatibility in cellular response for ZT1 BMG is comparable to Ti and its alloys. For gene expression of integrin β, ALP and COL I, mRNA level from osteoblast cells grown on ZT1 substrates is significantly higher than that on the CP-Ti and Ti64. It suggests that the adhesion and differentiation of osteoblasts grown on ZT1 are even superior to those on the CP-Ti and Ti64 alloy, then promoting bone formation. The good biocompatibility of ZT1 BMG is associated with the formation of zirconium oxide layer on the surface and good corrosion-resistance in physiological environment.     

Oxygen-stabilised partial amorphisation in a Zr50Cu50 alloy

Structural transitions on heating a ZrCu martensite prepared by induction melting and subsequent rapid cooling have been investigated by means of differential scanning calorimetry (DSC), electrical resistivity measurements, X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The ZrCu martensite firstly transforms to the ZrCu compound with the B2 structure at around 300°C. Depending upon the annealing temperature, there are two routes for the ZrCu compound to reach equilibrium. By annealing at T 425°C, the equilibrium state, i.e. a eutectoid mixture of Zr₇Cu₁₀ and Zr₂Cu, is attained directly because the required chemical segregation for the equilibrium phases can be satisfied; alternatively, by annealing at 300°C < T < 425°C, the equilibrium state is reached via another metastable state, an amorphous phase. This is, however, present only locally and contains significant levels of oxygen. A qualitative explanation of the observed structural transitions is given in terms of thermodynamic and kinetic considerations.     

Dynamic mechanical relaxation behavior of Zr35Hf17.5Ti5.5Al12.5Co7.5Ni12Cu10 high entropy bulk metallic glass

Non-equiatomic high entropy bulk metallic glasses were reported recently and show unique mechanical and physical properties.Dynamic mechanical relaxation behavior of Zr35Hf17.5Ti5.5Al12.5C07.5Ni12Cu10 high entropy bulk metallic glass was investigated by dynamic mechanical analysis(DMA)and the mechanical spectra could be well described by the quasi-point defects(QPD)theory.Compared to typical metallic glasses,the intensity of the β relaxation of Zr35Hf17.5Ti5.5Al12.5Co7.5Ni12Cu10 high entropy bulk metallic glass is lower due to the sluggish diffusion.At the same time,the correlation factor χ is higher than that of conventional metallic glasses and this is ascribed to the high configuration entropy.In paral-lel,physical aging below the glass transition temperature leads to a decrease of atomic mobility,caused by a decrease of the concentration of defects.