Thin Film Metallic Glasses Research Articles

Strain-and temperature-induced dilatancy in ZrNi thin film metallic glasses with nanoscale structural heterogeneities

Strain-and temperature-induced dilatancy in ZrNi thin film metallic glasses with nanoscale structural heterogeneities

Superior corrosion-resistant Zr-Ti-Ag thin film metallic glasses as potential biomaterials

Low-cost and non-cytotoxic ternary Zr-Ti-Ag thin film metallic glasses (TFMGs) were synthesized by DC magnetron sputtering. Results revealed that Ag addition enhanced the crystallization resistance and thermal stability of TFMGs. An appropriate Ag addition favored the mechanical property and corrosion resistance of TFMGs, while the excessive Ag addition had the opposite effect. Moreover, Ag did not directly form the passive film but altered the passive film stability and anti-corrosion capacity of TFMGs by inducing the disordered atomic arrangement, forming a dense microstructure, and tuning the corrosion-resistant Zr and Ti components. With low Young’s modulus of 116.2 GPa and passive current density of 0.45 × 10−7 A/cm2, the TFMG with an Ag target sputtering power of 11 W exhibited superior corrosion resistance, suggesting its application potential as biomaterials.

Glass and nanocrystalline phase formation in CuZrAg alloys: Insights from combinatorial thin film libraries studied by mapping synchrotron X-ray diffraction

We report detailed diffraction peak analysis and parameters indicative of the transition between fully amorphous microstructures and nanocrystal formation in sputter deposited thin film metallic glasses. Specifically, we fabricated ternary CuZrAg alloy films (2µm thickness) with a large compositional gradient on flexible, X-ray transparent polymer substrates in high vacuum conditions. The combinatorial libraries were subjected to point-by-point structural (XRD synchrotron radiation) and chemical (X-ray fluorescence spectroscopy) analysis, characterizing roughly 172 alloys. A strong correlation was found between peak symmetry and width, and early stages of crystalline phase formation. These nanocrystals are difficult to detect from the evolution of the peak position. In view of current literature, our data questions the recently claimed universality of the peak width as indicator of high glass forming ability. The addition of Ag significantly improves the poor glass formation of binary CuZr (36 alloys) under identical deposition conditions, as fully amorphous alloys are found for the majority of the investigated composition space. A thorough understanding of the microstructure of CuZrAg alloys on flexible substrates is highly relevant in view of favourable antibacterial properties and potential application as coatings for biomedical surfaces.

How to catch a shear band and explain plasticity of metallic glasses with continuum mechanics

Capturing a shear band in a metallic glass during its propagation experimentally is very challenging. Shear bands are very narrow but extend rapidly over macroscopic distances, therefore, characterization of large areas at high magnification and high speed is required. Here we show how to control the shear bands in a pre-structured thin film metallic glass in order to directly measure local strains during initiation, propagation, or arrest events. Based on the experimental observations, a model describing the shear banding phenomenon purely within the frameworks of continuum mechanics is formulated. We claim that metallic glasses exhibit an elastic limit of about 5% which must be exceeded locally either at a stress concentrator to initiate a shear banding event, or at the tip of a shear band during its propagation. The model can successfully connect micro- and macroscopic plasticity of metallic glasses and suggests an alternative interpretation of controversial experimental observations.

Sputtered zirconium based metallic glassy thin films onto electrospun PCL nanofibrous scaffolds for enriching bioactivity

Surface modification of electrospun Polycaprolactone (PCL) nanoscaffold is to enhance surface properties, particularly bioactivity. In this paper, electrospinning was employed to produce PCL nanoscaffolds and enhancing the bioactivity of the electrospun PCL scaffolds by sputtering of Zirconium based thin film metallic glasses (Zr -TFMGs). The Energy Dispersive Spectroscopy (EDS) analysis exhibited the presence of Zr, Ti and Si and surface topography by Atomic Force Microscopy (AFM) revealed the smooth surface of metallic glasses with nanofibrous structures. The sputtered samples were subjected to immersion test in Simulated Body Fluid (SBF) to analyze the apatite forming ability of Zr–Ti–Si metallic glasses. After 21days of incubation, SEM clearly showed the spherical structures of apatite formed on the surface of modified electrospun PCL. Cell viability studies using L929 fibroblast cells indicates the higher proliferation rate for the Zr based TFMG sputtered PCL scaffold specimen than the uncoated neat PCL scaffold and indicating the bioactive nature of Zr based TFMG. Contact angle of TFMG sputtered sample exhibited the hydrophobic surface which is helpful in preventing the biomedical devices from blood coagulation.

Characterizing oxidation, thickness, and composition of metallic glass thin films with combined electron probe microanalysis and X-ray photoelectron spectroscopy

Metallic glass thin films (MGTFs) are a recently developed class of alloy coatings with potential applications ranging from biomedical devices to electrical components. Their tribological performance in service conditions is dictated by MGTF bulk composition but can be limited by the native oxide surface that inevitably forms upon exposure to atmosphere. Surface oxidation, thickness, and composition of ZrCuNiAl MGTFs were characterized using a combination of X-ray photoelectron microscopy (XPS) and electron probe microanalysis (EPMA). MGTF samples with nominal thicknesses of 50, 500, and 1500 nm were sputtered onto Si and SiN wafer substrates within a high vacuum deposition chamber and their amorphicity was confirmed by X-ray diffraction. XPS depth profiling identified the thin film composition and showed that the surface oxide was dominated by a mixed layer of mostly ZrO2, a little oxidized Al, and some metallic Zr. EPMA X-ray intensities were acquired as a function of beam energy to excite characteristic X-rays from different depths of the MGTFs and reconstructed using open-source thin film analysis software BadgerFilm, to determine the composition and thickness of sample layers. EPMA results constrain the composition to be Zr54Cu29Al10Ni7 within 0.7 at. % variation and total thicknesses to be 49, 470, and 1546 nm. Using the oxide composition identified from XPS depth profiling as an input for BadgerFilm analysis, EPMA results indicate the surface oxidation layer on each of the thin film samples was 6.5 ± 1.1 nm thick and uniform across a 0.25 mm region of the film.

Mechanical responses and plastic rheological behavior of Ti–Zr-Hf-Co-Ni-Cu metallic glass thin films deposited with different substrate temperatures during nanoindentation and nanoscratch process

Ti–Zr-Hf-Co-Ni-Cu metallic glass thin films were deposited by magnetron sputtering at different substrate temperatures of 293 K, 373 K, and 473 K. All the thin films were indicated to be amorphous. The roughness was decreased from 0.71 ± 0.02 nm (293 K) to 0.65 ± 0.01 nm (473 K) and the thin film became more densified with fewer voids and defects. Consequently, the mechanical properties, plastic rheological behavior, and nanoscratch properties varied regularly with the microstructure at different substrate temperatures. The hardness and elastic modulus showed increasing trends with the elevated substrate temperature. The strain-rate strengthening effect occurred, causing the gradual disappearance of the pop-in event with the increasing strain rate. The cut-off value of strain burst size showed an increasing trend with the elevating strain rate. This trend was weakened with the elevated substrate temperature due to the decreased chaos of the interaction between atoms. The cut-off value also increased with the elevating substrate temperature. During the nanoscratch measurement, the elastic recovery ratio increased with the elevating substrate temperature. The critical stress for interface separation of the Ti–Zr-Hf-Co-Ni-Cu metallic glass thin film was improved from 1.9 N to 2.7 N with the substrate temperature rising from 293 K to 473 K.

Thermally stable Mo-Co-B thin film metallic glass as a potential diffusion barrier in Cu/Si contact system

Thin film metallic glass (TFMG) has demonstrated significant potential for applications in the semiconductor industry. In this work, fully amorphous Mo-Co-B thin films with a smooth surface and dense microstructure were prepared through magnetron sputtering. The thermal stability and diffusion barrier performance of the Mo-based TFMG were evaluated through vacuum annealing at temperatures ranging from 300 to 800 °C for 30 min. Nanoindentation tests were conducted to investigate the evolution of mechanical properties with annealing for the Mo-based thin film. When subjected to annealing at temperatures below 700 °C, the Mo-based thin film retained its fully amorphous structure. It displayed enhanced hardness and Young's modulus due to the annihilation of free volume with annealing. Increasing the annealing temperature to 700 °C and 800 °C resulted in surface oxidation and crystallization of the Mo-based TFMG, respectively, leading to a continuous decline in its mechanical properties. When employed as the diffusion barrier between Cu and Si, the Mo-based barrier layer effectively blocked the diffusion of Cu atoms through the barrier at temperatures below 800 °C. The failure of the barrier occurred at 800 °C due to the crystallization of the amorphous phase. Such excellent diffusion barrier performance of the thermally stable Mo-Co-B TFMG makes it a promising candidate as the barrier material in Cu metallization.

Better understand the crystallization dynamics of ZrCu TFMGs: Benefits of combining global and local in situ approaches

This work describes crystallization mechanisms in a model ZrCu thin film metallic glass, synthesized through magnetron sputtering. Global-scale characterization techniques, including differential scanning calorimetry and X-ray diffraction, are compared with local-scale characterization obtained through in situ transmission electron microscopy during isothermal heating. This multi-scale approach establishes the crystallization sequence of ZrCu thin film metallic glasses. Furthermore, it highlights the role of oxidation as a nucleation site, initiating the crystallization process. Once initiated, crystallization progresses as a propagating front, scanning and transforming the amorphous matrix. The combination of both global and local approaches yields consistent key thermodynamic values. Additionally, monitoring the advancing crystallization front during in situ high-temperature transmission electron microscopy provides access to crucial kinetic parameters, such as diffusion coefficients.

High-temperature Mo-based metallic glass thin films with tunable microstructure and mechanical behaviors

Developing high-temperature metallic glass thin films (MGTFs) with excellent combination properties is crucial for extending the practical applications of metallic glasses. A high-temperature multicomponent Mo-based MGTF with tunable microstructure prepared by single-target magnetron sputtering was presented in this study. Corresponding mechanical behaviors and thermal stability of MGTFs related to microstructure are systemically explored. By adjusting deposition parameters (pressure and power), the microstructure of as-deposited MGTFs can be altered from the dense homogeneous type to the loose nanoglass type. Such structure evolution can be explained by the competition between the surface diffusion and geometric shadowing effect. MGTFs with dense microstructure possess smaller surface roughness, higher hardness, higher Young’s modulus, and better wear resistance. Moreover, they also possess higher thermal stability where the fully amorphous structure and smooth surface can be well maintained after vacuum annealing at 1123 K for 30 min. By contrast, the MGTF with nanoglass microstructure shows inferior mechanical properties and thermal stability due to plentiful loose interface regions, providing abundant free volumes during deformation and acting as favorable crystal nucleation sites during annealing. The correlation between the microstructure and properties of as-deposited MGTFs is clarified with the universal scaling law of glasses. The annealing treatment distinctly increases the hardness and Young’s modulus of MGTFs. Meanwhile, after annealing, pop-in behaviors occur in the as-annealed MGTFs with dense microstructure but not in the as-annealed MGTF with nanoglass microstructure during the nanoindentation. These phenomena can be rationalized by the annihilation of free volumes during annealing and the evolution of the dynamical variable, shear transition zone, for the plastic deformation in MGTFs.

Effect of Zr content on the strain rate sensitivity of nanohardness of Ti-Zr-Cu-Ni-Al thin film metallic glass

The strain rate sensitivity of nanohardness of a magnetron sputtered Ti-Zr-Cu-Ni-Al thin film metallic glass has been investigated. Nanoindentation tests were performed at various loading rates on thin film metallic glasses with three different Zr content. Replacement of Ti with Zr has led to an increase in hardness due to higher atomic packing efficiency and stronger bonds. A non-serrated p-h curve independent of Zr content and a positive dependency of nanohardness on Zr content was observed. The negative strain rate sensitivity and enhancement of strain rate sensitivity with Zr content were discussed.

Effect of nanoheterogeneities on the fracture toughness and tensile ductility of CuTa metallic glass thin films

Nanoheterogenenous metallic glasses (MG) can offer improved ductility through a nanoscale modulation in their mechanical properties. However, the relationship between the modulation parameters and the mechanical behavior is not well understood. Physical vapor deposition can directly control the compositional and morphological parameters of nanoheterogeneous MGs and enables the systematic investigation of this problem. This work explores the microstructure and mechanical properties of a range of CuTa-based nanolayered amorphous/amorphous (A/A) and amorphous/semi-crystalline (A/SC) nanoheterogeneous MGs and MG composites. The first step was the identification of three microstructural regimes in CuTa, namely, a fully amorphous form (23–65 at.% Ta), a Ta-rich amorphous-crystalline composite (65–75 at.% Ta), and a Cu-rich amorphous-crystalline composite (16–23 at.% Ta). The hardness of the films increased from 6 GPa to 17 GPa with increasing Ta content. Next, a range of CuxTa1−x/CuyTa1−y nanolayers composed of A/A and A/SC nanolayers were investigated. The hardness of all nanolayers follows the rule of mixture. A/A structures do not provide a significant increase in fracture toughness and only a minor increase in tensile ductility despite the high amplitude modulation of hardness between layers. A/SC nanolayers’ hardness and toughness was higher than A/A nanolayers as well as monolithic amorphous films, but still remained below the monolithic Cu25Ta75 SC film. The results show that the design of nanoheterogeneities in MGs requires careful optimization to achieve a useful improvement in mechanical properties.

Polymorphous nanostructured metallic glass coatings for corrosion protection of medical grade Ti substrate

Metallic glasses have received attention in the world of materials science and engineering due to their high mechanical and tribological properties. Thin film nanostructured metallic glasses have shown great prospects as surface coatings with increasing applications in biomedical areas for implants and surgical devices. In this work, we deposited titanium- and zirconium-based polymorphous thin film metallic glasses (Ti–Fe–Cu, Zr–Fe–Al, Zr–W–Cu) on medical-grade polished titanium substrate by co-sputtering using a PVD system. The corrosion behaviour of the films was investigated by exposing the samples to sterile simulated body fluid and examined using electrochemistry, microscopy, and spectroscopic analyses. The polymorphic properties of the films after exposure to simulated body fluid were observed by SEM and TEM. SEM analysis shows that the surface morphology of the exposed samples was found to vary significantly compared to their corresponding as-deposited samples. Electrochemical properties (Ecorr, Icorr, and OCV, impedance |Z|) demonstrated that the thin film metallic glasses were found to enhance the corrosion resistance of the substrate. Further investigations of the exposed films by XPS and Raman analyses have revealed that the induced oxide passive layer significantly enhanced the corrosion efficacy of the films on titanium substrate. Among the three samples, Zr–W–Cu coating has shown the highest corrosion protection almost 450 times better than the bare titanium substrate.

Corrosion Properties of a Novel FeCrMoNbB Thin Film Metallic Glass Deposited by DC Magnetron Sputtering

The application of amorphous alloys as thin-film coatings with good corrosion properties has drawn attention in the last years since overcoming the typical limitations of these materials, such as the critical size and brittleness. Techniques based on Physical Vapor Deposition, like DC magnetron sputtering, are interesting once it allows parameter optimization to achieve the desired microstructure [1,2,3]. This study aims to characterize the electrochemical properties of a novel FeCrMoNbB (low Cr content – 11at%) alloy as a coating.Thin-film coatings were produced in a DC magnetron sputtering PVD system with 0.5 Pa Ar working pressure, 92 W of sputtering power, and 200°C deposition temperature. The substrate was 316L stainless steel. Corrosion tests were performed in a three-electrode cell in a Gamry 600+ potentiostat using the following sequence: two hours of open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) from 100kHz to 0,02 Hz, 20 minutes of OCP, and potentiodynamic polarization test from -0,03 to 1,2V (vs. OCP). The solution was a 0,6M NaCl (Cl- content equivalent to seawater), natural pH of 5.5. Measurement Model software, developed by Orazem et al. [4], was used for data regression. X-ray photoelectron microscopy (XPS) was performed to obtain complementary information about the passive film. An XR3E2 apparatus from Vacuum Generator with an Mg-Kα source was used. The analysis was performed after stabilization in an open circuit for two hours.Fully amorphous thin films of about 400 nm were obtained. Outstanding corrosion behavior was observed for the coating, which presented a corrosion current (icorr) around 5 x10-9 Acm-2 and a corrosion potential of 127 mV. The icorr value is more than two decades lower when compared to the 316L of the substrate, indicating a higher corrosion resistance after applying the coating. EIS results showed a high impedance modulus at low frequency was |Z|LF = 3.7 MΩ.cm2. XPS analysis showed that all the alloying elements were in the oxidized form on the surface. Metallic species from the underlying surface could also be detected, meaning the oxide layer has less than 10 nm. Regression with Measurement Model software found a global capacitance C = 5.7 μF.cm2, a typical value for a compact passive layer. From the value of C, the film thickness was estimated to be around 2 nm, corroborating with the XPS analysis. A compact, thin layer of oxide composed of Cr, Nb, and Mo can be associated with high protectiveness of the passive film, hence, good corrosion resistance. Furthermore, the pitting phenomenon typical of 316L near 500mV was not observed in the coating. In summary, the results are promising for using these alloys as coatings for marine applications, potentially replacing conventional stainless steels.[1] M. Panayotova, Y. Garbatov, C. Guedes Soares, Corrosion of Steels in Marine Environment, Monitoring and Standards, Safety and Reliability of Industrial Products, Systems and Structures, Taylor & Francis Group, 2008.p.370.[2] WOOD Maureen; VETERE ARELLANO Ana Lisa; VAN WIJK Lorenzo. Publications Office of the European Union; 2013. JRC84661[3] Chu, J. P. et al. Thin film metallic glasses: Unique properties and potential applications. Thin Solid Films 520, 5097–5122 (2012).[4] M.E.O. W. Watson, EIS: Measurement Model Program., ECSarXiv. (2020). https://doi.org/10.1149/osf.io/kze9x.

The Fabrication and Evaluation of a Capacitive Pressure Sensor Using Ru-Based Thin Film Metallic Glass with Structural Relaxation by Heat Treatment

Microelectromechanical systems (MEMS)-based capacitive pressure sensors are conventionally fabricated from diaphragms made of Si, which has a high elastic modulus that limits the control of internal stress and constrains size reduction and low-pressure measurements. Ru-based thin-film metallic glass (TFMG) exhibits a low elastic modulus, and the internal stress can be controlled by heat treatment, so it may be a suitable diaphragm material for facilitating size reduction of the sensor without performance degradation. In this study, a Ru-based TFMG was used to realize a flattened diaphragm, and structural relaxation was achieved through annealing at 310 °C for 1 h in a vacuum. The diaphragm easily deformed, even under low differential pressure, when reduced in size. A diaphragm with a diameter of 1.7 mm was then applied to successfully fabricate a capacitive pressure sensor with a sensor size of 2.4 mm2. The sensor exhibited a linearity of ±3.70% full scale and a sensitivity of 0.09 fF/Pa in the differential pressure range of 0–500 Pa.

Biocompatibility screening of Mo–Si–Ta glassy alloy films sputtered on additive manufactured Ti–6Al–4V implant prototypes and PCL scaffolds

A ternary system of amorphous alloy with the components Mo, Ti, and Si with the composition Mo54Si33Ta13 has been chosen as the surface coating for the implantable materials to improve Ti6Al4V bioactivity. Ti6Al4V alloy metal powders were used to create the implant prototypes with the 3D metal printer. With the aid of a DC magnetron, the films are sputtered onto the implant prototypes. Elemental composition, amorphous nature, surface chemistry and topography of the as-fabricated microstructure films were comprehensively analysed using X-ray diffraction analysis, X-ray photoelectron spectroscopy and electron/atomic force microscopic techniques. The mechanical properties were studied from Nano indentation method. The coatings were confirmed to be cytocompatible determined from the in-vitro biocompatibility investigations using human osteosarcoma cells. The electrochemical corrosion studies carried out in SBF showed the higher corrosion resistance for the thin film metallic glass (TFMG)-coated customized 3D printed Ti-alloy implants than the pristine specimen.

Mechanical property evaluation of thin film metallic glasses via molecular dynamics and finite element analyses

This study presents a method for extracting free-volume model (FVM) parameters of Zr-based thin film metallic glasses (TFMG) using the molecular dynamics (MD) and finite element analyses (FEA). Nano-tension MD simulations are performed to obtain the first two elastic properties of thin film, i.e., Young's modulus and Poisson's ratio. The other two main FVM parameters (reference stress and pressure dependent coefficient) are determined by systematically matching FE stress-strain curves to those from MD analyses with the finite element model updating (FEMU) method. Nanoindentation FEA and experiments are performed with Zr-based TFMG specimens to validate the estimated FVM parameters. It demonstrates that the combined MD/FEA approach is not only simpler, but also more efficient than previous methods in obtaining all primary parameters.

Annealing-induced changes in wear resistance and nanomechanical properties of CuZr metallic glass thin films

Over recent years, metallic glass thin films (MGTFs) have found extensive applications in advanced micro-engineering systems. Consequently, there is a need to thoroughly assess the nanomechanical and tribological behaviors of MGTFs to optimize the design of efficient components. In this study, we employed the nanoindentation technique in various modes to investigate the elastic heterogeneity, tribological response, and mechanical properties of CuZr amorphous films. Before conducting the mechanical tests, annealing treatments at 500 K and 600 K were performed to create samples with different stored energies. The thermal history analysis revealed that the annealing process reduced the stored energy in the microstructure. Furthermore, the pre-annealing treatment resulted in increased hardness and Young’s modulus of the thin films. Additionally, higher annealing temperatures significantly improved the wear resistance of the MGTFs. Observing the serration dynamics in the scratching test, we noticed that the annealing treatment induced larger shear bands on the wear track side. Moreover, the increase in annealing temperature led to a reduction in elastic heterogeneity, which was consistent with the enthalpy relaxation values in the samples. This suggests that the annealing temperature enhanced the densely packed atomic structure, leading to the stabilization of the thin films.

Vein pattern vs. columnar fracture shape in Cu-Zr thin film metallic glasses: Driving force and mechanism

Numerous studies have been published in the past showing the presence of vein-like or columnar fracture shapes in thin film metallic glasses (TFMGs), while the reason behind the different features remains poorly understood. This study uncovers the reason behind this phenomenon in Cu-Zr TFMGs’ by considering experimental evidence and analysis. Oxidation during deposition is the reason for the presence of the columnar feature after the cleavage, as shear banding cannot raise the temperature enough for the regional melting process to end up in the vein pattern. In several studies, unnoticed or unreported oxygen is proposed to be the reason for reporting metallic glasses' columnar cross-sections.

Effects of RF Magnetron Sputtering Power on the Mechanical Behavior of Zr-Cu-Based Metallic Glass Thin Films.

Zirconium-based metallic glass films are promising materials for nanoelectronic and biomedical applications, but their mechanical behavior under different conditions is not well understood. This study investigates the effects of radio frequency (RF) power and test temperature on the nanostructure, morphology, and creep behavior of Zr55Cu30Al10Ni5 metallic glass films prepared by RF magnetron sputtering. The films were characterized by X-ray diffraction and microscopy, and their mechanical properties were measured by a bulge test system. The results show that the films were amorphous and exhibited a transition from noncolumnar to columnar morphology as the RF power increased from 75 W to 125 W. The columnar morphology reduced the creep resistance, Young's modulus, residual stress, and hardness of the films. The creep behavior of the films was also influenced by the test temperature, with higher temperature leading to higher creep strain and lower creep stress. The findings of this study provide insights into the optimization of the sputtering parameters and the design of zirconium-based metallic glass films for various applications.