Zirconium-based Bulk Metallic Glass Research Articles

Unusually high erosion resistance of zirconium-based bulk metallic glass

Abstract

Effects of annealing on the compositional heterogeneity and structure in zirconium-based bulk metallic glass thin films

In-situ heating fluctuation electron microscopy and scanning transmission electron microscopy have been utilized to study compositional and structural heterogeneities in Zr51Cu32Al9Ni8 thin films upon annealing. Composition fluctuations are present in the as-deposited thin films. Well below the glass transition temperature, the composition fluctuations increase with annealing time. Short- and medium-range order also change with annealing temperature. The observed heterogeneities in the glass structure persist until annealing causes crystallization. The 20nm thick Zr51Cu32Al9Ni8 films contain oxide layers both at the surface and the film/substrate interface with the total thickness of 7–8nm. In-situ annealing increased the oxygen content of the whole films to about 24wt.% after 2h at 400°C.

Zirconium based bulk metallic glass—Better resistance to slurry erosion compared to hydroturbine steel

The slurry erosion behavior of a zirconium based bulk metallic glass, Zr44Ti11Cu10Ni10Be25, was evaluated in this study. Slurry erosion tests were carried out using a non-circulating type test rig at impingement angles of 30°, 60°, and 90°. Commonly used hydroturbine steel was evaluated under the same test conditions. At 30° impingement angle, the metallic glass demonstrated nearly 2.6 times higher erosion resistance compared to the steel. At normal impingement, the metallic glass was marginally better. Lower erosion rates of the bulk metallic glass at oblique impingement angles was attributed to its significantly higher hardness and deformation induced partial devitrification. For normal impingement, material was removed in the form of fragments from highly strained platelets due to limited plasticity of bulk metallic glasses. The metallic glass demonstrated a brittle mode of erosion with higher erosion rate at higher angle of impingement. In contrast, hydroturbine steel showed ductile mode of erosion under the same test conditions.

Nanometer-Scale Heterogeneities of the Structure of Zirconium-Based Bulk Metallic Glasses

Structure of amorphous alloys ZrTiCuNiBe and ZrTiCuNiAl is studied by means of low-field ion and combined field-emission microscopy. In both alloys the structural heterogeneities of nanometer-scale are clearly revealed. The surface layers formed by field evaporation possess a cellular structure. The cells have polygonal shape with transverse size ranging from 2 nm to 20 nm. It is established that variance of the local energy of field evaporation is of 0%–5% in the cell body. A local minimum of the field evaporation energy is observed within the cell boundaries (intercluster boundaries). In the minimum the depth is measured to be of 0.8 eV.

Modeling size effects on fatigue life of a zirconium-based bulk metallic glass under bending

A size effect on the fatigue-life cycles of a Zr50Cu30Al10Ni10 (at.%) bulk metallic glass has been observed in the four-point-bending fatigue experiment. Under the same bending-stress condition, large-sized samples tend to exhibit longer fatigue lives than small-sized samples. This size effect on the fatigue life cannot be satisfactorily explained by the flaw-based Weibull theories. Based on the experimental results, this study explores possible approaches to modeling the size effects on the bending-fatigue life of bulk metallic glasses, and proposes two fatigue-life models based on the Weibull distribution. The first model assumes, empirically, log-linear effects of the sample thickness on the Weibull parameters. The second model incorporates the mechanistic knowledge of the fatigue behavior of metallic glasses, and assumes that the shear-band density, instead of the flaw density, has significant influence on the bending fatigue-life cycles. Promising predictive results provide evidence of the potential validity of the models and their assumptions.

Contributions of atomic diffusion and plastic deformation to the plasma surface activation assisted diffusion bonding of zirconium-based bulk metallic glass

A mathematical model was established to estimate the contributions of atomic diffusion and plastic deformation to the diffusion bonding of zirconium-based bulk metallic glasses. Additionally, the surface state was introduced into the model since oxide film is the main barrier to atomic bonding across interface. The model calculation displayed that the contribution of plastic deformation to void closure was six orders of magnitude higher than atomic diffusion. The joints with ion etching before bonding were achieved to verify the model. The experimental strength of joints had a sound fit with the theoretical strength calculated by the model.

Numerical and experimental studies on the shear band intervention in zirconium based bulk metallic glass composites Zr53Cu22Ni9Al8Ta8

The Zr53Cu30−xNi9Al8Tax (x = 2, 4, 6, 8) bulk metallic glass composites (BMGCs) rods had been demonstrated their superior mechanical performance in our recent study due to the presence of micro- (10–30 μm) and nano-sized (10–80 nm) Ta-rich particles produced by the in-situ precipitation. These uniformly distributed particles in the amorphous matrix acted as scattered obstacles to effectively impede and deflect the propagation of shear bands and thus avoid catastrophic failures of materials. However, how the shear bands deform and evolve under different levels of loading and the quantitative description of such phenomenon is yet an amenable question for engineering designs. In this study, the selected Zr53Cu22Ni9Al8Ta8 BMGCs rods with size of 2 mm in diameter was plastically deformed by compression at different strain level, namely, 3%, 8%, 15% and 25%, to investigate the interactions between the Ta-rich macro particles and shear banding. Corresponding numerical analyses on the compression test and on a small element from SEM images of deformed rods were also performed to provide a quantitative measure on the experimental observations.

Effect of the ultrasound action on the acoustic emission and mechanical properties of zirconium-based bulk metallic glasses

The effect of preliminary ultrasound action on the mechanical properties and features of the structure of zirconium-based bulk metallic glasses has been studied by the method of acoustic emission under uniaxial compression. Results of studies have been interpreted using the polycluster model of the structure of amorphous metallic alloys. Analysis of the obtained data has allowed us to substantiate the mechanism of the change in the structure and strength of metallic glasses as a result of alternating-sign mechanical loading with an ultrasound frequency of 20 kHz.

Role of aluminum as an oxygen-scavenger in zirconium based bulk metallic glasses

In order to investigate a way to diminish the impact of oxygen onto the critical cooling rate of Zr-based alloys, the bonding chemistry of the elements in Zr-Cu-Ni-Al-Nb-Si bulk metallic glasses with different oxygen contents is studied by x-ray photoelectron spectroscopy. Complementary undercooling experiments lead to continuous-cooling-transformation diagrams for the studied alloys. The experimental results demonstrate that Al not only acts as a scavenger for both absorbed and intrinsic oxygen but the dissolution of its oxide on atomic length scales refrains from heterogeneous nucleation. The combined effect is an enhancement of oxygen tolerance in the investigated alloy.

Design of multi materials combining crystalline and amorphous metallic alloys

Multi materials, associating zirconium based bulk metallic glasses and crystalline metallic alloys like magnesium alloys or copper are elaborated by co-deformation processing performed in the supercooled liquid regions (SLR) of the bulk metallic glasses. Two processes are investigated: co-extrusion and co-pressing. In the first case, filamentary composites with various designs can be produced whereas in the second case sandwich structures are obtained. The experimental window (temperature, time) in which processing can be carried out is directly related to the crystallisation resistance of the glass which requires getting information about the crystallisation conditions in the selected metallic glasses. Thermoforming windows are identified for the studied BMGs by thermal analysis and compression tests in their SLR. The mechanical properties of the produced multi materials are investigated thanks to specifically developed mechanical devices and the interfaces between the amorphous and the crystalline alloys are characterised.

Development of Tensile Ductility of Zirconium-Based Bulk Metallic Glass at Room Temperature by Thermoplastic Deformation

Bulk metallic glass (BMG) is a kind of alloy with amorphous structure and it has better thermal stability because of its atomic composition. In particular, zirconium-based BMGs are expected to apply for structural materials, because they exhibit excellent mechanical properties, a high corrosion resistance, etc. BMGs exhibit a brittle fracture behavior caused by the rapid propagation of a shear band under tensile load at room temperature (RT). On the other hand, BMGs show the high formability due to very large plastic deformation under high temperature condition. And sometimes BMGs are crystallized by thermoplastic deformation even though its thermal condition is never beyond the time-temperature-transformation (TTT) curve of the material. When crystalline particles make the propagation of the shear band stop and deflect, such an effect can bring about an apparent inelastic strain under the tensile load at RT. In this study, the development of the ductile property with the inelastic strain of Zr55Cu30Al10Ni5 BMG at RT was attempted by applying crystallization with thermoplastic deformation. The experimental results suggested that the thermoplastic deformation with strain rate of 2.0 × 10-4s-1 or 3.0 × 10-3s-1 can bring about the inelastic strain to Zr55Cu30Al10Ni5 BMG at RT under tensile loading by precipitating the crystalline particles in the material.

Electrochemical and surface investigation of zirconium based metallic glass Zr 59Ti 3Cu 20Al 10Ni 8 alloy in nitric acid and sodium chloride media

To understand the corrosion behavior of zirconium based bulk metallic glass (BMG); electrochemical, and surface investigations were carried out on Zr 59Ti 3Cu 20Al 10Ni 8 alloy in HNO 3 acid, and NaCl medium. Electrochemical studies were carried out in 1 N, 6 N and 11.5 N HNO 3 by recording open circuit potential–time, potentiodynamic polarization, and impedance characteristics. Atomic force microscope was used for e x situ surface morphology study of the specimens after potentiodynamic polarization in 1 N, 6 N, and 11.5 N HNO 3, and in situ surface morphology study by free immersion of the specimens in both 0.5 M, and 1 M NaCl solution. The results revealed attaining of steady state noble open circuit potential, wider passive region, and decrease in transpassive potential ( E transpass) with increase in HNO 3 concentration. Surface morphology in free immersion, and after polarization showed, deep pit propagation in both 0.5 M, and 1 M NaCl solution, and aggressive surface dissolution in HNO 3 medium.

Inherent strength of zirconium-based bulk metallic glass

The polycluster morphology and inherent tensile strength of bulk metallic glass Zr 41Ti 14Cu 12.5Ni 10Be 22.5 in the as-cast state were determined by means of high-field mechanical loading using field ion microscopy. The two-level cluster structure with the length scale of the order of 2 and 10 nm was revealed. It was disclosed that the strength of this alloy is characterized by a strong size-effect in a nanometer scale range. It is shown that within this size region the Weibull distribution is not suitable to describe the scale effect. It is ascertained that the limit level of shear strength of the examined glass is 5.8 GPa, and shear strength of a separate cluster may be estimated as 6.7 GPa.

Using thermoforming capacity of metallic glasses to produce multimaterials

In addition to casting, thermoforming is a particularly interesting way to produce components in bulk metallic glasses since large strains can be achieved when the BMGs are deformed in their supercooled liquid region. The experimental window (temperature, time) in which high temperature forming can be carried out is directly related to the crystallization resistance of the glass. Such forming windows have been identified for zirconium based bulk metallic glasses thanks to thermal analysis and compression tests in the supercooled liquid region. Based on this identification, the thermoforming capacity of the studied glasses was used to produce multimaterials associating metallic glasses with conventional metallic alloys. Two processes have been preferentially investigated (co-extrusion and co-pressing) and the interface quality of the elaborated multi materials was studied.

Mechanical properties of a co-extruded Metallic Glass/Alloy (MeGA) rod—Effect of the metallic glass volume fraction

A Metallic Glass/Alloy (MeGA) rod with a core in zirconium-based bulk metallic glass and a sleeve in aluminium alloy has been successfully elaborated by co-extrusion. SEM observations of the cross-section of the rod show that the interface between the glass and the alloy is defect-free. Compression tests are carried out at room temperature on the MeGA rods containing various glass volume fractions. The yield stress is well described by the rule of mixtures which combines the strength of the glass and that of the alloy, suggesting isostrain behaviour as could be expected. During compression, a good mechanical bonding is observed in the MeGA-rod even after the first fracture of the metallic glass. Finally, push-out tests are performed to evaluate the bonding quality between the two materials. Large values of the shear strength are measured which confirms that co-extrusion leads to good bonding between the glass and the aluminium alloy.

Biocompatibility Study of Zirconium-Based Bulk Metallic Glasses for Orthopedic Applications

Bulk metallic glasses (BMGs) represent an emerging class of materials that offer an attractive combination of properties, such as high strength, low modulus, good fatigue limit, and near-net-shape formability. The BMGs have been explored in mechanical, chemical, and magnetic applications. However, little research has been attracted in the biomedical field. In this work, we study the potential of BMGs for the orthopedic repair and replacement. We report the biocompatibility study of zirconium (Zr)–based solid BMGs using mouse osteoblast cells. Cell attachment, proliferation, and differentiation are compared to Ti-6Al-4V, a well-studied alloy biomaterial. Our in-vitro study has demonstrated that cells cultured on the Zr-based BMG substrate showed higher attachment, alkaline phosphatase activity, and bone matrix deposition compared to those grown on the control Ti alloy substrate. Cytotoxicity staining also revealed the remarkable viability of cells growing on the BMG substrates.

Simple Shear Test of Zirconium-Based Bulk Metallic Glass and Yield Surface at Room Temperature

As-cast bulk metallic glasses fracture without plastic strain under tensile loading at room temperature. However, it is inferred from molecular dynamics calculation that the yield surface of the glass is similar to that of one of the ductile metals. In this study, uni-axial tensile, uni-axial compressive, and simple shear tests were carried out for zirconium-based bulk metallic glass at room temperature and the yield surface (the fracture surface) was inspected experimentally. As a result, the deformation of the zirconium-based bulk metallic glass at room temperature is dominated mainly by shear stress just like in the case of a ductile metal.

612 ジルコニウム基バルク金属ガラスの常温引張特性の改善(GS 材力・材料1)

612 ジルコニウム基バルク金属ガラスの常温引張特性の改善(GS 材力・材料1)

Influence of minor aluminum concentration changes in zirconium-based bulk metallic glasses on the elastic, anelastic, and plastic properties

The Poisson’s ratio of Zr-based bulk metallic glasses in the system Zr63−xCu24AlxNi10Co3 was found to exhibit a non-monotonous behavior as a function of x when measured with ultrasound by the pulse–echo technique. In addition, from wave propagation velocity measurements at different frequencies, i.e. f = 2.25 MHz and f = 10 MHz, a composition-dependent anelastic behavior as a function of x is found, exhibiting a similar non-monotonous behavior. In this work we further investigated the plastic deformation and the creep properties of this glass system in compression tests and by nanoindentation. The plastic strain and the measured creep deformation show correlations with the Poisson’s ratio. We then discuss the anelastic behavior observed while measuring the sound-wave propagation velocity in the frame of the thermoelastic damping and the bond reorientation as proposed by Egami. Finally we discuss these effects with regard to X-ray diffraction analysis.

Processing of Zirconium-Based Bulk Metallic Glass (BMG) Using Micro Electrical Discharge Machining (Micro-EDM)

A zirconium-based bulk metallic glass was machined by micro electrical discharge machining (micro-EDM) to demonstrate its feasibility under discharge energies typical of the microregime. Furthermore, input energies of 13.4 µJ and 0.9 µJ, and three different tool electrodes, namely, tungsten rod electrode, copper, and brass tube electrodes were employed to elucidate the effects of different machining conditions on the machined surface roughness, burr width, and tool wear. Experimental results showed that using the lower input energy reduced surface roughness by 43%–51% and burr width by 63%. Moreover, results also suggested that, at lower input energies, tube electrodes experienced lower tool wear ratios than rod electrodes.