Thin Film Metallic Glasses Research Articles

Initial Morphology and Feedback Effects on Laser-Induced Periodic Nanostructuring of Thin-Film Metallic Glasses.

Surface nanostructuring by femtosecond laser is an efficient way to manipulate surface topography, creating advanced functionalities of irradiated materials. Thin-film metallic glasses obtained by physical vapor deposition exhibit microstructures free from grain boundaries, crystallites and dislocations but also characterized by a nanometric surface roughness. These singular properties make them more resilient to other metals to form laser-induced nanopatterns. Here we investigate the morphological response of Zr65Cu35 alloys under ultrafast irradiation with multipulse feedback. We experimentally demonstrate that the initial columnar microstructure affects the surface topography evolution and conditions the required energy dose to reach desired structures in the nanoscale domain. Double pulses femtosecond laser irradiation is also shown to be an efficient strategy to force materials to form uniform nanostructures even when their thermomechanical properties have a poor predisposition to generate them.

Evaluation of mechanical properties of Zr–Cu–Al–Ni TFMG using nanoindentation

Nanomechanical properties of thin-film metallic glasses (TFMG) with various thicknesses can be evaluated through nanoindentation experiments. In this study, zirconium based TFMG (Zr-TFMG, Zr 65 Cu 15 Al 10 Ni 10 ) is deposited on various substrates and then, the effects of film thickness and substrate type on material property evaluation are investigated. Free volume model (FVM) is employed to consider the pressure-dependent behavior such as shear band and softening of Zr-TFMG. FVM parameters of Zr-TFMG were determined by matching the numerical load-depth curves with experimental ones. Significant pile-up on Si substrate, while sink-in on soda-lime glass substrate, implies that deformation behavior of Zr-TFMG depends on the substrate type. Growth of free volume with increasing thickness influences the evaluated FVM parameters.

ZrCuAg Thin-Film Metallic Glasses: Toward Biostatic Durable Advanced Surfaces.

A combinatorial approach has served as a high-throughput strategy to identify compositional windows with optimized desired properties. Here, ZrCuAg thin-film metallic glasses were deposited by DC magnetron sputtering. For the purpose of using these coatings as biomedical surfaces, their durability in terms of mechanical and physicochemical properties as well as antibacterial properties were characterized. The effect of the chemical composition of thin films was studied. In particular, two key parameters were highlighted: the atomic ratio of Zr/Cu (with three values of 65/35, 50/50, and 35/65) and the silver content (from 1 to 16 at. %). All thin films are XRD amorphous and exhibit a typical veinlike pattern, which is characteristic of metallic glasses. They also show a dense and smooth surface and a hydrophobic behavior. Mechanical properties are found to be deeply influenced by the Zr/Cu ratio and the atomic structure. Although a low Zr/Cu ratio and/or a high silver content is detrimental to corrosion behavior, it favors the bactericidal effect of thin films. For all Zr/Cu ratios, ZrCuAg thin-film metallic glasses with silver contents higher than 12 at % are fully bactericidal. For lower silver contents, the bactericidal effect progressively decreases, which paves the way for a biostatic behavior of these surfaces.

The role of nano-scale elastic heterogeneity in mechanical and tribological behaviors of a Cu–Zr based metallic glass thin film

Despite its significance in fundamentally understanding mechanical behaviors of metallic glasses, the effect of elastic heterogeneity on plastic deformation and thereby nanotribological behavior of metallic glass thin films (MGTFs) remains an open question. By a combination of nano-scratch, nano-DMA and nanoindentation tests, we have investigated in the present work the room-temperature inhomogeneous plastic deformation behavior and nanotribological properties of Cu–Zr based MGTFs obtained by magnetron sputtering with different substrate temperatures. It is revealed that while the studied MGTF experiences a moderate rise of both hardness and Young's modulus with the elevating substrate temperature from 300 K to 473 K, its wear resistance significantly increases during the nano-scratch under a ramping load. More interestingly, through systematically studying the serration dynamics during the nano-scratch for MGTFs with different thermal history, we found that the increase of critical length scale for shear banding, which is well accompanied by the reduction of nano-scale elastic heterogeneity, tends to make shear banding more difficult in the amorphous structure, and thus enhance the wear resistance of the tested MGTFs. The current findings may provide a useful guidance to develop MGTFs with a superior mechanical and tribological properties via tuning their nanoscale elastic heterogeneity.

Anisotropic and size-dependent mechanical responses of free-standing Ni-Nb metallic glass thin film

Via in-situ tensile test, we demonstrated a brittle-to-ductile transition of Ni-Nb metallic glass (MG) thin films when the film thickness decreased from 363 nm to 87 nm. The elastic strain limit of 4.7% and apparent work hardening behavior were seen for free-standing 87 nm-thick film. Contrary to quenched MGs, anisotropic mechanical response existed in MG thin films with nanocolumnar structure owing to the deteriorated bonding strength of column boundaries.

Biological performance of metal metalloid (TiCuZrPd:B) TFMG fabricated by pulsed laser deposition

The aim of our study is to investigate the effect of boron with different ratios in Ti-Cu-Pd-Zr metallic glass (MG) matrix (Ti-Cu-Pd-Zr:B) fabricated by Pulsed Laser Deposition (PLD) for biomedical implants. The Ti based Thin Film Metallic Glasses (TFMGs) in combination with boron (in different atomic %) was assessed in attaining the combined properties, like outstanding corrosion resistant properties and good biocompatibility in this work. The disordered structure and amorphous nature of the Ti-Cu-Pd-Zr:B thin films systems were achieved by the PLD process and affirmed by XRD and transmission electron microscopy. The boron incorporation in the TFMG has been elucidated by XPS analysis. The boron containing films displays distribution of boron protuberances interleaved in the amorphous matrix was stated from SEM analysis. It is found that increase in atomic percentage of boron contents in TFMG results in the improvement in glass transition temperatures. The electrochemical parameters suggest better corrosion resistance and capabilities of passivity when boron percentage was increased in the film thereby preventing adverse biological reactions. TFMGs exhibited excellent hemocompatibility by preventing the platelet activation. MTT assay manifests increase in cell concentration with culture period on the TFMGs for the MC3T3‐E1 preosteoblasts cells. Cell morphology was also studied which confirmed the viable state of the cells on the TFMG surfaces. The combination of such distinctive properties marks these TFMG systems as prospective aspirants for biomedical implants.

ZrCuAlNi thin film metallic glass grown by high power impulse and direct current magnetron sputtering

Abstract High-power impulse magnetron sputtering (HiPIMS) is a thin film deposition technique that combines the advantages of energetic deposition methods with magnetron sputtering. HiPIMS has so far mostly been utilized for the growth of crystalline coatings. Here we offer a study devoted to metallic glasses, in which we compare Zr60Cu25Al10Ni5 (target composition) thin films deposited by conventional direct current magnetron sputtering (DC) and HiPIMS. Film microstructure is strongly dependent on the choice of the sputtering method. The DC layers show a columnar structure with intra-columnar porosity, which provides a pathway for oxygen diffusion into the film. In contrast, HiPIMS films are column-free and possess about 4% higher density, as revealed by X-ray reflectivity. Electron diffraction reveals a decrease in average atomic spacing for the latter film of about 12%. These differences in film properties and morphology can be attributed to an increase in ad-atom mobility during HiPIMS caused by an increase in ion energy and flux of the film-forming species enabling a more efficient energy and momentum transfer to the growing film surface. The relative contribution of metallic and hence film forming ions to the overall ion flux of the DC plasma compared to the HiPIMS plasma is 13% and 96%, respectively. Additionally, a substrate bias causes the ionized film forming species during HiPIMS to arrive close to the substrate normal reducing shadowing effects. Different microstructures have a direct effect on the average roughness values, which for DC and HiPIMS films are 1.4 nm and 0.2 nm, respectively. The indentation hardness H and Young's modulus E are higher for the HiPIMS sample, at 9.2 ± 0.3 GPa and 131.6 ± 3.6 GPa, respectively. The increase in hardness for the HiPIMS sample as compared to the DC sample (~35%) can be attributed to higher film density, compressive (HiPIMS) as opposed to tensile (DC) stress and the lack of a columnar structure.

Fe-based thin film metallic glass as an activator of peroxymonosulfate for azo dye degradation

Abstract In this work Fe39Co39Si8B14 thin film metallic glasses (TFMGs) of thickness ranged between 122– 475 nm were deposited by magnetron sputtering on a commercial filter paper to act as a peroxymonosulfate (PMS) activator for degradation of Orange G (OG) azo dye. Degradation of 98.6% was achieved in 16 min. The influence of parameters such as catalyst dosage, light irradiation intensity, dye and PMS concentration to the efficiency of degradation were also investigated. SEM and XPS results revealed that the outstanding performance was attributed to the abundance of amorphous zero valent metals given by the amorphous atomic packing structure of TFMG. Zero valent metals readily activated PMS and favored the generation of SO4• and •OH radicals, which were the responsible species in degrading OG dye molecules. Another contribution was from the fibrous and porous texture of the filter paper substrate which provides specific surface area as high as 1.152 m2/g. TFMG-coated filter paper also showed good reusability that repeated degradation was possible. Results suggests that applying TFMG on a textured substrate could drastically reduce the dosage of Fe-based metallic glass needed compared to its powder or foil counterparts, which is significantly more cost effective.

Varying kinetic stability, icosahedral ordering, and mechanical properties of a model Zr-Cu-Al metallic glass by sputtering

${\mathrm{Zr}}_{65}{\mathrm{Cu}}_{27.5}{\mathrm{Al}}_{7.5}$ metallic glass thin films with widely varying kinetic stability as a function of deposition rate were synthesized by single-target direct current magnetron sputtering. Fluctuation electron microscopy and angular correlations in coherent electron nanodiffraction show that glasses with increased stability have increased nanoscale structural order, particularly of icosahedral character. The most kinetically stable film's reduced modulus was 22% higher than a glass of the same composition rapidly quenched from the liquid, consistent with increased density and improved thermodynamic stability. These results suggest that enhanced nanoscale icosahedral order contributes both to the kinetic stability of the glass and its resistance to mechanical deformation.

Correlation between internal states and creep resistance in metallic glass thin films

Some mechanisms of creep, especially those involving dislocations for many crystalline materials, can be verified by direct microstructural examination. However, metallic glass thin films (MGTFs) are disordered materials lacking the long-range order of crystals. Even today, the creep mechanisms for amorphous alloys are far from being fully understood. The physical factors governing localization and instability during creep deformation are still elusive. In this work, Ni60Nb40 alloys with high kinetic stability were prepared by magnetron sputtering at different substrate temperatures to obtain MGTFs with different internal states. We report a close correlation between the internal states and the creep resistance of the MGTFs and reveal that altering the substrate temperature during magnetron sputtering can induce changes in the surface morphologies, plastic deformation resistance, and creep resistance of Ni60Nb40 MGTFs. The creep deformation mechanism is interpreted based on the shear transformation zone (STZ) model of amorphous alloys, and our results may have implications for understanding the role of STZs during creep deformation of MGTFs.

Enhanced Mechanical Properties of Metallic Glass Thin Films via Modification of Structural Heterogeneity.

The structure of Cu50Zr50 and Co56Ta35B9 metallic glass thin films (MGTF) was effectively tailored via various applied substrate temperatures by means of the magnetron sputtering technology. Obviously enhanced hardness and elastic modulus are achieved by different compositional MGTFs by increasing the substrate temperature. Compared with the CuZr MGTFs, the CoTaB MGTF deposited at 473 K displays the smaller strain-rate sensitivity exponent, m, and a weaker spectrum intensity based on the nanoindentation creep test, suggesting its better creep resistance. In addition, the STZ volume of the CoTaB MGTF significantly decreases after depositing at higher temperature. According to the nano-scratch analysis, the CoTaB MGTF at the substrate temperatures of 473 K performs the shallower scratch width and the larger H3/E2 value, indicating its better tribological property.

Combinatorial measurement of critical cooling rates in aluminum-base metallic glass forming alloys

Direct measurement of critical cooling rates has been challenging and only determined for a minute fraction of the reported metallic glass forming alloys. Here, we report a method that directly measures critical cooling rate of thin film metallic glass forming alloys in a combinatorial fashion. Based on a universal heating architecture using indirect laser heating and a microstructure analysis this method offers itself as a rapid screening technique to quantify glass forming ability. We use this method to identify glass forming alloys and study the composition effect on the critical cooling rate in the Al–Ni–Ge system where we identified Al51Ge35Ni14 as the best glass forming composition with a critical cooling rate of 104 K/s.

Fabrication and properties evaluation of novel Fe46-XCr23Mo14Co7PXB5Si5 (X=0, 6) m metallic glasses deposited by DC magnetron sputtering

Novel Fe46Cr23Mo14Co7B5Si5 and Fe40Cr23Mo14Co7P6B5Si5 thin film metallic glasses (TFMGs) were successfully deposited using direct current magnetron sputtering process. Different microstructural evaluations were carried out including XRD, FE-SEM, EPMA, AFM, and TEM-SAED. Mechanical properties such as nano-indentation and fracture toughness tests were also performed on different substrates and under various applied forces. In addition, corrosion performance was carried out by potentiodynamic polarization, potentiostatic and electrochemical impedance spectroscopy tests. Formation of full, glassy phase was confirmed by XRD as well as TEM-SAED for both films. It was found that adding P element changed the cross-sectional growth of TFMG, decreased surface roughness and improved mechanical properties. It was also shown that the substrate type had minor influence on the fracture toughness values of TFMGs as compared to the applied force. P addition also led in an excellent corrosion resistance and significantly increase in polarization resistance, with more than 400 times as compared to the one for SS304 substrate.

Magnetron sputtered magnesium-based thin film metallic glasses for bioimplants.

Mg-based thin film metallic glasses (TFMGs) can viably decrease stress shielding caused by mismatch of the modulus of elasticity between the implant material and human bone. Here, Mg-based TFMGs were fabricated onto implantable substrates by ion assisted pulsed DC magnetron sputtering. The microstructure assessment and the impact of the principle constituents of the coatings were determined utilizing an x-ray diffractometer, a transmission electron microscope, and x-ray photoelectron spectroscopy. The hardness of these thin films was estimated to be 5.1 GPa. In vitro degradation tests including electrochemical studies and immersion tests in simulated body fluid revealed that the presence of zinc could raise the corrosion resistance of Mg-based TFMG. Indirect in vitro cytotoxicity using L929 fibroblast cells revealed that the TFMGs did not induce any toxicity in cells. Biomineralization experiments using Saos-2 cells promoted the formation of calcium phosphate on its surface.

Effect of Hybridization in PdAlY-(Ni/Au/Ir) Metallic Glasses Thin Films on Electrical Resistivity

Thin film metallic glasses (MGs) are promising materials for electronic applications. While the transport properties of MGs are composition dependent, the influence of hybridization on the resistivity has not been investigated systematically. We implement a correlative experimental and computational approach utilizing thin film deposition, electrical resistivity measurements, synchrotron X-ray diffraction and ab initio calculations to explore the relationship between the fraction of hybridized bonds present in PdAlY-M glasses with M=Ir,Au,Ni, where the electrical behaviour is dominated by d-electrons. The strong bonds hybridization in PdAlY-Ir yields a high resistivity of 175 µΩm, while the weakly hybridized bonds in PdAlY-M MGs (M=Au,Ni) result in lower resistivities of 114 and 92 µΩm, respectively. We propose that an increase in the fraction of hybridized states yields an increased room temperature resistivity. Whereas nearly-free electron model applies to the weakly hybridized systems, where the density of states at the Fermi level determines the resistivity.

Electrical and Optical Properties of Co75Si15B10 Metallic Glass Nanometric Thin Films.

Co-based (Co75Si15B10) thin-film metallic glass (TFMG) with nanometric thicknesses (100~300 nm) was investigated for its structural, electrical, and optical properties. The TFMG structure was examined using scanning electron microscopy and X-ray diffraction, while electrical properties were examined using inductance/capacitance/resistance spectroscopy, cyclic voltammetry, and Hall effect measurements. In addition, optical absorption/reflection/transmittance measurements were performed to examine optical properties. Results revealed that Co-based TFMGs, which have an amorphous structure without surface defects, behave like a dielectric material, with higher resistivity and much lower carrier concentration than pure cobalt (Co) thin films of the same thickness, despite its mobility being modestly larger than its Co counterparts. Meanwhile, the optical investigation of TFMG enabled us to determine the complex relative permittivity (complex relative dielectric constant) at a visible wavelength (632.8 nm). Moreover, unlike normal metals, TFMGs exhibited a large positive value of the real part of , while exhibiting properties of substantial absorption of light (absorption coefficient α). It was also found that the Co-based TFMG gained optical transparency for thicknesses less than 5 nm. TFMGs demonstrated the nearly thickness-independent properties of the electrical and optical parameters probed, a feature of high-index, dielectric-like material with negligible size effects, which may have applications in micrometer-scaled optoelectronic and magneto-optical devices.

Corrosion protection of NiNb metallic glass coatings for 316SS by magnetron sputtering

Metallic glasses (MGs) appear as promising anti-corrosion coating materials due to their microstructural and physicochemical advantages. Herein, we proposed magnetron sputtered NiNb thin film MG coatings (MGCs) with different structures and compositions for corrosion protection of 316 stainless steel in an aggressive saline environment. The properties of monolayered Ni50Nb50 and Ni60Nb40, as well as the multilayered Ni50Nb50/Ni60Nb40 (at.%) MGCs, were characterized in terms of morphology and microstructural properties, as well as the anticorrosion behavior. All the NiNb MGCs presented compact structure and the monolayered coatings exhibited preferable adhesion properties in comparison with the multilayered coating. The electrochemical tests and XPS results imply that the monolayered Ni50Nb50 MGC with high Nb content resisted corrosion mainly due to the formation of stable passive film that contained abundant Nb2O5 species, whereas the Ni60Nb40 MGC with high Ni content showed week corrosion protection performance during long-term service due to the dissolution of Ni cations and the devastation of the coating structure. Though with bit worse adhesion and more vulnerable Ni60Nb40 layers, the multilayered Ni50Nb50/Ni60Nb40 MGC possessed comparable corrosion resistance with the monolayered Ni50Nb50 MG coating, which remained stable even after 32 days of exposure. Such performance should be ascribed to the combined eff ;ect of the repassivation property for the sub-layers, the hindrance of propagation paths of micro-defects, and the obstruction of corrosive species by interfaces in the multilayered coating.

Improved Mechanical Properties and Corrosion Resistance of Mg-Based Bulk Metallic Glass Composite by Coating with Zr-Based Metallic Glass Thin Film

Mg-based bulk metallic glass (BMG) and its composite (BMGC) can be excellent candidates as lightweight structure materials, but lack of anti-corrosion ability may restrict their application. In order to enhance the natural weak point of Mg-based BMGC, a 200-nm thick Zr-based metallic glass thin film (MGTF) ((Zr53Cu30Ni9Al8)99.5Si0.5) was applied and its mechanical properties as well as its corrosion resistance were appraised. The results of a 3-point bending test revealed that the flexural strength of the Mg-based BMGC with 200-nm thick Zr-based MGTF coating can be greatly enhanced from 180 to 254 MPa. We propose that the Zr-based MGTF coating can help to cover any small defects of a substrate surface, provide a protecting layer to prevent stress concentration, and cease crack initiation from the specimen surface during bending tests. Moreover, the results of anti-corrosion behavior analysis revealed a similar trend between the Mg-based BMG, Mg-based BMGC, and Mg-based BMGC with Zr-based MGTF coating in 0.9 wt.% sodium chloride solution. The readings show a positive effect with the Zr-based MGTF coating. Therefore, the 200-nm thick Zr-based MGTF coating is a promising solution to provide protection for both mechanical and anti-corrosion behaviors of Mg-based BMGC and reinforce its capability as structure material in island environments.

Preclinical studies of non-stick thin film metallic glass-coated syringe needles

Our objective in this study was to determine the biocompatibility and hemocompatibility of thin film metallic glass (TFMG) and its potential use in hypodermic needles for intramuscular or intravenous injection. Mouse and rabbit models were employed under approval from the Institutional Animal Care and Use Committee (n = 5/group, two groups in total for both animal models). Platelet-rich plasma (PRP) was collected from the whole blood of rabbits (ear vein) without anti-coagulant for use in in vitro coagulation tests. Histological analysis and optical microscopy were used to assess the endothelial structure of the inner lining of veins after being punctured with needles and detained for 3 days. Histological analysis of ear vein sections revealed that the extent of endothelial damage after puncturing with a TFMG-coated needle was 33% less than that produced by bare needles. Our results confirm that the deposition of a thin TFMG layer (e.g., Zr53Cu33Al9Ta5) on the surface of hypodermic needle can have remarkably clinical benefits, including anti-adhesion, reduced invasion, and minimal endothelial damage. Our results also confirm the good biocompatibility and hemocompatibility of the TFMG coatings.

Microstructural characterization and properties of a Ti-Ta-Si-Ni metallic glass surface alloy fabricated on a TiNi SMA substrate by additive thin-film electron-beam method

An important factor limiting the wide application of thin-film metallic glass (TFMG) coatings for improving the surface-sensitive properties of structural alloys is the poor adhesion of TFMG to substrates. This problem can be overcome through the synthesis of MG surface alloys (MGSAs) by additive pulsed electron-beam melting of film/substrate systems of high glass-forming ability. In this work, this approach is applied to the [film (Ti60Ta30Si10, at.%, 100 nm)/substrate (TiNi alloy)] system using a low-energy, high-current electron beam (~2.5 μs, ~15 keV, 1.7 J/cm2) at 10 synthesis cycles and 10 pulses per cycle. Using SEM/WDS, XRD and cross-sectional HRTEM/EDS/SAED analyses it has been found that ~1.5 μm thick SA has completely MG structure, in which the near-surface ~500 nm thick Ni-depleted layer has composition ~Ti56Ta23Ni11Si10. Beneath the MGSA, the ~200 nm thick nanocomposite Ti50Ni30÷40(Ta + Si)20÷10 sublayer, consisting of Ti2Ni nanograins embedded in the amorphous phase is formed. The nanocomposite sublayer is followed by the intermediate sublayer with the eutectic columnar nano-grain B2-structure, which provides the diffusion bonding of MGSA with unmelted TiNi substrate. The monotonic depth dependences of hardness, elastic modulus, depth recovery ratio and plasticity, obtained by indentation, indicate the mechanical compatibility of the MGSA and underlying sublayers with the TiNi substrate. The adhesion-related failure of the MGSA during scratch testing proceeds in the ductile mode mainly through the plastic flow of intermediate sublayer. Evaluation of shape memory effect and superelasticity by torsional deformation technique has shown that synthesis of the MGSA results in an almost 2-fold increase in the martensitic shear stress and significant decrease in the stress hysteresis width compared with the untreated TiNi samples. The irreversible residual strain is ~0.8% at a maximum strain of 6%. Potentiodynamic polarization measurements have shown that synthesis of the MGSA results in the significant enhancement in corrosion resistance of test samples in the Lock-Ringer salt solution.