Thin Film Metallic Glasses Research Articles

Confinement Effects on the Spatially Inhomogeneous Dynamics in Metallic Glass Films.

This work develops the elastically collective nonlinear Langevin equation theory to investigate, for the first time, the glassy dynamics in capped metallic glass thin films. Finite-size effects on the spatial gradient of structural relaxation time and glass transition temperature (Tg) are calculated at different temperatures and vitrification criteria. Molecular dynamics is significantly slowed down near rough solid surfaces, and the dynamics at location far from the interfaces is sped up. In thick films, the mobility gradient normalized by the bulk value obeys the double-exponential form since interference effects between two surfaces are weak. Reducing the film thickness induces a strong dynamic coupling between two surfaces and flattens the relaxation gradient. The normalized gradient of the glass transition temperature is independent of vitrification time scale criterion and can be fitted by a superposition function as the films are not ultrathin. The local fragility is found to remain unchanged with location. This finding suggests that one can use Angell plots of bulk relaxation time and the Tg spatial gradient to characterize glassy dynamics in metallic glass films. Our computational results agree well with experimental data and simulation.

Highly Elastic and Corrosion-Resistive Metallic Glass Thin Films for Flexible Encapsulation.

Ternary CuZrTi metallic glass thin films synthesized by sputtering are suggested as highly flexible and corrosion-resistant encapsulation materials. Unlike nanocrystalline Cu and binary CuZr metallic glass thin films, the ternary CuZrTi metallic glass thin films retain amorphous structure and do not oxidize even after 1000 h in an accelerated harsh environment at 85 °C with 85% relative humidity. The encapsulation performance of 260 nm thick ternary CuZrTi metallic glass is maintained even after 1000 bending cycles at a 3% tensile strain, corresponding to 70% of the elastic deformation limit, according to the results of a uniaxial tensile test. Because of the enhanced mechanical flexibility and reliability of the ternary CuZrTi metallic glass thin films, they have been applied to flexible organic solar cells as an encapsulation material.

Influence of substrate type and film thickness on the failures of Zr-based thin-film metallic glass under nanoscratch

Nanoscratch experiments under constant and ramp loading conditions are performed to investigate the delamination, and spallation characteristics of Zr-based thin-film metallic glass (Zr-based TFMG, Zr65Cu15Al10Ni10). TFMGs with different film thickness = 200, 500, 1000 nm are deposited over hard and soft substrates via DC magnetron sputtering process. Coefficient of friction (COF) is measured to be less about 0.03 regardless of scratch mode and maximum normal load. The critical load for thin film delamination and spallation reveals that the deformation and failure mechanism of Zr-based TFMG significantly change with film thickness and substrate type. The failure mechanism is characterized by observing the scratch grooves via optical and scanning electron microscopes (SEM). The adhesion energy between thin film and soft substrate is calculated based on Burnett and Rickerby model, and an increase in adhesion energy with interfacial layer thickness is reported.

Nanoheterogeneous ZrTa metallic glass thin films with high strength and toughness

This study investigated the mechanical behavior of ZrxTa1−x (x = 21–79 at%) thin films and nanolayered films of ZrTa with modulated composition as model systems to gain insight into the hardness and toughness of metallic glasses and metallic glass nanocomposites. The monolithic films exhibit two primary microstructures, namely, a fully amorphous form (Zr = 35–70at%.) and an amorphous-crystalline composite (21–30 at% Zr). The amorphous films show a monotonic hardness variation with composition over a wide range of 5.5 – 9 GPa. The partial crystallization of the films results in a further jump in hardness, as opposed to the general trend of softening upon crystallization. The emergence of the crystalline phase also improves the ductility of the films, as verified by nanoindentation-based fracture toughness measurements. The indentation pile-up exhibits several shear bands in the fully amorphous films, replaced by a featureless pile-up zone for the case of Zr25Ta75, further verifying the superior toughness of the composite. The second part of the analysis pursued obtaining a similar toughening through fully amorphous nanolayered films of Zr35Ta65 / Zr70Ta30. The results indicate that these films provide a balanced combination of high hardness and enhanced ductility, providing an alternative route to the development of tough metallic glass coatings. Data AvailabilityThe raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.

Effect of modulation ratio on the mechanical behavior of multilayer-thin-film metallic glasses

This study investigates the effect of modulation ratio on the mechanical characteristics of multilayer zirconium-based thin film metallic glasses (Zr-based TFMG) by nanoindentation and finite element (FE) method. Multilayer TFMGs (Zr–Cu–Al–Ni and Zr–Cu–Ag) with different modulation ratio (λ = thickness of layer 1/layer 2) are deposited on silicon (Si) wafer substrates by magnetron sputtering. The load-depth responses of TFMGs to nanoindentation are observed in both experiments and FE simulations, in which pressure dependent free-volume-model (FVM) is employed for TFMGs. The changes in mechanical behavior with film thickness, layer pattern, modulation ratio and indentation depth are compared between single and multilayer TFMGs. It is demonstrated that an appropriate selection of layer pattern and modulation ratio can improve the mechanical performance of multilayer TFMG systems. The proposed FE model can be utilized for tailoring multilayer thin film deposition for achieving maximum mechanical performance of TFMG coated products.

Imprintable Au-Based Thin-Film Metallic Glasses with Different Crystallinities for Surface-Enhanced Raman Scattering

Imprintable Au-Based Thin-Film Metallic Glasses with Different Crystallinities for Surface-Enhanced Raman Scattering

Electrochemical response in physiological environments and mechanical properties of Ti51Si24Ni14Nb11 and Fe40Ti30Al18Si12 thin film metallic glasses

This work investigates electrochemical response and mechanical properties of quaternary Ti51Si24Ni14Nb11 and Fe40Ti30Al18Si12 (at.%) thin film metallic glasses (TFMGs) developed using magnetron co-sputtering. Both TFMGs demonstrate superior corrosion resistance registering ∼7 to 10 times smaller corrosion current density, ∼200 to 800 mV higher break-down potential, and ∼4 to 6 times higher charge transfer resistance in phosphate buffer saline (PBS) and 0.9% sodium chloride (NaCl) compared to conventional Ti- and Fe-based biomaterials, e.g., commercially pure Ti (cp-Ti) and 316L stainless steel (SS). The enhanced anti-corrosive behavior of the quaternary films is attributed to their amorphous structures and relatively more protective passive oxide films. In addition, nano-indentation experiment reveals more than 2 times higher hardness and ∼10 to 40 GPa lower elastic modulus of the TFMGs compared to conventional biomaterials. The combination of obtained anti-corrosive behavior and mechanical properties promotes the fabricated films as potential candidates for future bio-implant applications.

Corrosion resistance and thermal stability of sputtered Fe44Al34Ti7N15 and Al61Ti11N28 thin films for prospective application in oil and gas industry

Fe-and Al-based thin-film metallic glass coatings (Fe44Al34Ti7N15 and Al61Ti11N28) were fabricated using magnetron co-sputtering technique, and their corrosion performances compared against wrought 316L stainless steel. The results of GI-XRD and XPS analyses demonstrated amorphous structure and oxide layer formation on the surface of the fabricated thin films, respectively. The potentiodynamic (PD) polarization test in chloride-thiosulfate (NH4Cl ​+ ​Na2S2O3) solution revealed lower corrosion current (Icorr) (0.42 ​± ​0.02 ​μA/cm2 and 0.086 ​± ​0.001 ​μA/cm2 Vs. 0.76 ​± ​0.05 ​μA/cm2), lower passivation current (Ipass) (1.45 ​± ​0.03 ​μA/cm2 and 1.83 ​± ​0.07 ​μA/cm2 Vs. 1.98 ​± ​0.04 ​μA/cm2), and approximately six-fold higher breakdown potential (Ebd) for Fe- and Al-based coatings than those of wrought 316L stainless steel. Electrochemical Impedance Spectroscopy (EIS) of both films showed 4- and 2-fold higher charge transfer resistance (Rct), 7- and 2.5-times higher film resistance (Rf), lower film capacitance values (Qf) (10 ​± ​2.4 ​μS-sacm-2, and 5.41 ​± ​0.8 ​μS-sacm-2 Vs. 18 ​± ​2.21 ​μS-sacm-2), and lower double-layer capacitance values (Qdl) (31.33 ​± ​4.74 ​μS-sacm-2, and 15.3 ​± ​0.48 ​μS-sacm-2 Vs. 43 ​± ​4.23 ​μS-sacm-2), indicating higher corrosion resistance of the thin films. Cyclic Voltammetry (CV) scan exhibited that the passive films formed on the Fe- and Al-based coatings were more stable and less prone to pitting corrosion than the wrought 316L stainless steel. The surface morphology of both films via SEM endorsed the CV scan results, showing better resistance to pitting corrosion. Furthermore, the thermal analysis via TGA and DSC revealed the excellent thermal stability of the thin films over a wide temperature range typically observed in oil-gas industries.

Inverse size effects in un-notched and notched metallic glass thin films

The sample size effect on the deformation behaviors of metallic glasses (MGs) attracts a lot of interest. Here, a series of molecular dynamics simulations have been performed on un-notched and notched MG thin films to fully investigate the influence of sample thickness on their fracture strengths and failure mechanisms. With decreasing sample thickness, the failure strength of un-notched MG thin films decreases slightly and the failure mode changes from shear banding to homogeneous deformation. In contrast to this brittle-to-ductile transition observed in un-notched MG thin films, shear banding prevails for notched MG thin films regardless of sample thickness. Concurrently, a notch strengthening effect is observed in the notched MG thin films when the sample thickness falls close to the shear band (SB) thickness. This significant notch strengthening is due to the failure mode transition from homogeneous deformation in un-notched MGs to shear banding in notched MGs. Based on the energetic model, a theoretical analysis is proposed to rationalize the size effect on failure mechanism transitions of both un-notched and notched MG thin films. The present study offers an understanding of size effect on the un-notched and notched MG thin films, as well as useful guidelines for the design, testing, and engineering of MG for microelectromechanical applications.

Novel Ta46.5W35Co18.5 thin film metallic glass with excellent corrosion resistance, high hardness and good thermal stability

Thin film metallic glasses (TFMGs) have attracted great attention due to their excellent functional properties and ease of fabrication as compared with bulk metallic glasses. Among them, TaW-based TFMGs have rarely been studied so far. Here, a novel Ta46.5W35Co18.5 TFMG was successfully developed using a magnetron co-sputtering system. The Ta46.5W35Co18.5 TFMG exhibits high hardness of 12.3 GPa, high elastic modulus of 159 GPa, pronounced plastic deformation behavior, and excellent corrosion resistance, i.e., low passive current density of 7.65 × 10−6 A/cm2 and high corrosion potential of 0.31 V, as well as good thermal stability with high onset crystallization temperature of 1100 K. In addition, the origin of these excellent properties was also investigated in detail by using X-ray diffraction and high-resolution transmission electron microscopy. It was found that, for the Ta46.5W35Co18.5 TFMG, its excellent corrosion resistance may be attributed to the amorphous structure, and the high hardness and good plastic deformation ability are caused by the unique atomic-scale structure with nanocrystals dispersed in the amorphous matrix. This work provides a useful guideline for developing TFMG system combined with excellent corrosion resistance, high hardness, and good thermal stability.

Generation of cytocompatible superhydrophobic Zr-Cu-Ag metallic glass coatings with antifouling properties for medical textiles.

Zirconium–Copper-based metallic glass thin films represent promising coatings in the biomedical sector for their combination of antibacterial property and wear resistance. However, finding a Zr–Cu metallic glass composition with desirable cytocompatibility and antibacterial property is extremely challenging. In this work, we have created a cytocompatible and (super-)hydrophobic Zr–Cu–Ag metallic glass coating with ≈95% antifouling properties. First, a range of different chemical compositions were prepared via Physical Vapor Deposition magnetron by co-sputtering Zr, Cu, and Ag onto a Polybutylene terephthalate (PBT) substrate among which Zr93·5Cu6·2Ag0.2, Zr76·7Cu22·7Ag0.5, and Zr69·3Cu30·1Ag0.6 were selected to be further investigate for their surface properties, antibacterial activity, and cytocompatibility. Scanning electron microscopy (SEM) images revealed a micro-roughness fibrous structure holding superhydrophobic properties demonstrated by specimens' static and dynamic contact angle measurements ranging from 130° to 150°. The dynamic contact angle measurements have shown hysteresis below 10° for all coated samples which indicated the superhydrophobicity of the samples. To distinguish between antifouling and bactericidal effect of the coating, ions release from coatings into Luria Bertani Broth (LB), and Dulbecco's Modified Eagle Medium (DMEM) solutions were evaluated by inductively coupled plasma mass spectrometry (ICP-MS) measurements after 24 ​h and 5 days. Antifouling properties were evaluated by infecting the specimens' surface with the Gram-positive Staphylococcus aureus and the Gram-negative Escherichia coli strain reporting a ≈95% reduction of bacteria adhesion as visually confirmed by FESEM and fluorescent live/dead staining. Human mesenchymal stem cells (hMSC) were used for direct cytocompatibility evaluation of coated samples and their metabolic activity was evaluated via relative fluorescence unit after 24 ​h and 5 days confirming that it was comparable to the controls (>97% viable cells). The results were further visualized by FESEM, fluorescent staining by Live/Dead Viability/Cytotoxicity Kit and confirmed the cytocompatibility of all coated samples. Finally, hMSC′ cytoplasm was stained by May Grunwald and Giemsa after 5days to detect and visualize the released ions which have diffused through the cells' membrane.

Nanoimprinting of magnetic FeCo-based metallic glass thin films

The ability to create submicron/nanoscale patterns with magnetic alloys at low cost is difficult. Here, we demonstrate a method to create such patterns using Fe40Co35P10C10B5 metallic glass thin films. The viscous workability of a metallic glass thin film was used to make patterns with dimensions up to ~100 nm using the nanoimprinting technique, and the effects of the patterning on the magnetic properties of the metallic glass thin films were investigated. An increase in the out-of-plane coercivity (~380 Oe) and remanent magnetization (Mr = ~12% of the saturation magnetization, Ms) were observed for amorphous thin films patterned with a high density of nano-dots. This effect was observed because of changes to the magnetic shape anisotropy induced by the nano-imprinting. Two events of magnetization reversal were confirmed in the crystalline films of the same alloy. The reversal of magnetization under the low magnetic field of ~100 Oe corresponds to soft magnetic phases, whereas that at 2400 Oe corresponds to the hard magnetic phase. Recoil curve measurements suggest that the average magnetization-switching field of hard magnetic grains in the film was between 2800 and 3600 Oe. Based on our experimental results and analysis, we suspect the presence of tetragonal Fe–Co hard/semihard magnetic phase in crystalline thin films. We believe that the low-cost and large-area micro- to nanoscale patterning ability of the present magnetic thin films are promising for the development of various magnetic MEMS and memory devices.

Bioactivity and <italic>in</italic> <italic>vitro</italic> degradation behavior of MgZnCa thin-film metallic glass

<p indent="0mm">Magnetron sputtering was used to prepare MgZnCa thin-film metallic glass (MG), and a single roller melt-spinning method was used to prepare amorphous MgZnCa ribbon. Potential polarization curves of MgZnCa amorphous ribbon and bulk high-purity magnesium (HP Mg) in simulated body fluids were compared using electrochemical tests. The corrosion resistance of MgZnCa MG is found to be significantly better than that of HP Mg, which is mainly attributed to its higher corrosion potential and lower corrosion current density. Immersion experiments, hydrogen evolution experiments, X-ray diffraction, Raman spectroscopy, and scanning electron microscopy were used to analyze the structure and composition of MgZnCa thin-film MG (TFMG) before and after corrosion, showing that the release rate of hydrogen was the fastest in the first hour, with active magnesium and calcium on the film’s surface preferentially dissolved. Furthermore, the appearance of a zinc-rich phase in the corrosion film and the increase in local pH promotes the precipitation of phosphate, which can improve the corrosion resistance of MgZnCa MG. <italic>In</italic> <italic>vitro</italic> experiments show that the 25% concentration extract obtained after soaking the MgZnCa MG has higher cell viability and lower apoptosis rate than the control medium, indicating that the MgZnCa MG is biocompatible. Therefore, with excellent corrosion resistance and biocompatibility, MgZnCa MG can be used as bioactive coatings on the surface of biologically inert materials.

Real-time high-temperature scanning indentation: Probing physical changes in thin-film metallic glasses

This work reports the use of a new high-temperature scanning indentation (HTSI) technique to monitor the physical changes occurring in thin-film metallic glasses (TFMGs) in situ during heat treatment at the local scale. Using this technique, based on high-speed nanoindentation performed during thermal cycles, the entire mechanical evolution with temperature of a binary model ZrCu TFMG was characterized in only a few hours. This approach enabled clear identification of the physical evolutions of the amorphous coatings in only one indentation experiment, highlighting in particular the metallic glass-to-supercooled liquid transition and crystallization process. In addition, the brittle-to-ductile transition was precisely characterized, with remarkable agreement with the literature. Moreover, the mechanical response of the ZrCu thin film was assessed in situ throughout the entire supercooled liquid stage, providing key kinetic information. Nanohardness measurements also enabled the crystallization fraction to be computed over time during the crystallization process. In addition, differential scanning calorimetry and high-temperature X-ray diffraction were performed for comparison purposes, with excellent agreement with the HTSI results. Through this model out-of-equilibrium thin-film study, both the efficiency and robustness of HTSI were demonstrated, providing a better understanding of the thermally activated mechanisms of small-scale systems.

Oxidation of metallic glass thin films: a combined EPMA and XPS investigation into the composition and thickness of oxidized surfaces

Oxidation of metallic glass thin films: a combined EPMA and XPS investigation into the composition and thickness of oxidized surfaces

Fabrication and characterization of metallic glass nanotube array as in application of wound dressing

Currently, wound dressing is often used to accelerate wound healing, avoid contaminations from the external environment and protect wound from infections, control moisture around the wound, meanwhile being biocompatible and non-toxic. Thin film metallic glass (TFMG) possess amorphous structure that driven to several unique properties such as excellent strength and high surface smoothness. Zr-based (Zr63.5Cu19.9Al11.5Ni5.1 (at%)) and W-based (W65.4Ni30.5B4.1) metallic glasses were selected as the candidate of nanotube array in this study. A layered structure Zr/W/Zr-based TFMGs were deposited on a nanotube array template and then fabricated into MeNTA and applied as a substrate of wound dressing. Hyaluronic acid (HA) and hyaluronic acid/ gold nanoparticles (HA/AuNPs) composite were loaded into the MeNTA under vacuum ambient. Animal test was conducted on live pigs in order to observe the improvement in wound healing and wound biopsy by attaching drug-loaded MeNTA. After loading the drugs into nanotubes array, significant change in diameter and surface appearance of nanotube is observed. In the animal test, both HA and HA/AuNPs loaded MeNTA accelerated wound healing process up to 96.4% and 90.5%, respectively.

Nanostructure optimization of Zr-W-Ti metallic glass thin films via multitarget co-sputtering with oblique angle deposition approach

In this work, we systematically investigated the Zr-W-Ti nanostructured metallic glasses (NMGs) thin films on silicon (Si) wafer substrate fabricated via multitarget co-sputtering with oblique angle deposition (OAD) technique. By varying the substrate angles (θs) from 0° to 55°, the evolution of Zr-W-Ti NMGs from dense to nanocolumnar and nanorod film were observed by field-emission scanning electron microscope (FE-FEM), which created by the self-shadowing effect. The critical point of substrate angles was around 15° to produce the nanocolumnar and 40° to form the nanorod structure. The relationship among the substrate angles and the Zr-W-Ti NMGs tilted angle (β) was determined and discussed in detail with two theoretical correlations as the "Tangent rule" and "Cosine rule." The X-ray photoelectron spectroscopy (XPS) studied revealed the different chemical compositions. The results obtained from grazing incidence X-ray diffraction (GIXRD) and transmission electron microscope (TEM) indicated that the prepared Zr-W-Ti NMGs thin films exhibit an amorphous structure. Ultimately, it suggests that the multitarget co-sputtering with the OAD technique provides NMGs thin films, enabling applications in gas storage and sensor devices due to their well-defined nanostructured morphological and chemical composition characteristics.

Bio-compatible Zirconium-based thin film metallic glasses with nitrogen reinforced by micro-alloying technique

In this study, a brand new compositional combination of Zr-Ti-Si-N thin film metallic glasses (TFMGs) was successfully demonstrated that, showing novel properties, such as no grain boundaries that help to decrease the coefficient of friction, to enhance hardness and modulus; especially its non-toxic, and bio-compatible behaviours. Zirconium, Titanium, and Silicon as non-toxic agents were chosen to form TFMGs according to its atomic radius and electro-negativity. Micro-alloying technique was applied to well blend elements through multi-target sputtering with superior cooling rate to enhance thin films remaining in amorphous state. This provides the ability to create TFMGs with good mechanical properties and bio-compatibility. Futher more, Nitrogen was introduced as the fourth dopant to increase the glass forming ability and improve the stability in order to enhance its mechanical performance as good as traditional Zr-Cu-Ni-Al TFMGs. The evaluation of cytotoxicity test was cultered with Escherichia coli (E-Coli) by observing the shapes and survival numbers to detect if the metallic ions contained toxicity released. The in-vitro bio-compatibility test was applied by co-culturing with human skeletal muscles. Through observing the adhesion and complete coverage of human skeletal muscles, the potentiality and possibility of Zr-Ti-Si-N TFMG can be figured out and used for medical implanting applications.

Natural aging of Ni60Nb40 metallic glass thin film: Evolution of microstructure and mechanical properties

Since metallic glass thin films (MGTFs) are commonly used in the atmosphere of air, the study on the evolution of structure, morphology, and mechanical properties of MGTFs exposed to air is of great significance for the practical application of MGTFs. The oxide formation mechanisms are investigated by experimental and calculation methods in this work. The results indicated that the crystalline oxide NiNb2O6 can be formed when exposed to air. The crystal structure of the oxide is orthorhombic, and the lattice constants can be calculated as: a = 14.022, b = 5.675 and c = 5.015 nm. The oxide NiNb2O6 was initiated around the amorphous island-like boundary during natural aging. The island boundary of amorphous matrix can provide the formation condition of nucleation and growth for crystalline oxide. The averaged Young's modulus and hardness of NiNb2O6 oxide are much higher than that of the amorphous matrix based on the results of experiments and first-principle calculations, indicating that the presence of crystalline oxides might improve the wear-resistance performance of the films.

Morphology of cracks and shear bands in polymer-supported thin film metallic glasses

Here we provide a systematic study of tensile deformation mechanisms in PdSi metallic glasses employing polymer-supported sputter deposited films. Due to the polymer substrate, global strain localization within one critical shear band is inhibited and thus thousands of different shear bands and cracks can be examined within a single tensile sample. Two distinctly different types of shear bands, allowed by the sample geometry, are observed and analyzed. It is shown that crack formation occurs through activation of multiple out-of-plane shear bands leading to local plasticity and neck-like shape of crack edges. The in-plane shear bands, which appear at higher applied strains, typically do not lead to crack formation and can accommodate both applied tensile strain and transverse compressive strain. The mechanism of effective strain hardening through de-activation of in-plane shear bands is demonstrated by means of quasi-in-situ studies. Shear banding is shown to be the fundamental deformation mechanism for different film thicknesses ranging from 25 to 1000 nm. Polymer-supported films represent a unique model material system which enables easy characterization of the tensile behavior of metallic glasses and provides an opportunity to gain new insights into the fundamental mechanisms of shear banding.