Zirconium-based Bulk Metallic Glass Research Articles

Nanoindentation and relaxation behavior of nitrogen doped zirconium based bulk metallic glass

In this paper, the effect of nitrogen doping on the mechanical properties of Zr-based bulk metallic glasses (BMGs) was studied by nano indentation experiment, and the correlation mechanism between microstructure evolution and mechanical properties was analyzed. The results show that the serrations events exhibited by metallic glasses during nanoindentation are related to the loading rates. With the decreasing loading rate, more obvious serrations events occur in the loading segment, which is attributed to the sufficient time for shear bands to multiply and propagate at low rates. The addition of nitrogen will induce the generation of more flow defects. Compared with BMGs without nitrogen, the nitrogen-doped Zr-based BMGs exhibit more serration events due to introducing more flow defects to form the shear transformation zones (STZs) and subsequently facilitating the shear bands to multiply. The possible relationships between the structural evolution, shear band initiation and propagation, and relaxation behavior of nitrogen doped and non doped metallic glasses were discussed.

Mechanism of chip segmentation transition from shear slip to shear fracture of Zirconium-based bulk metallic glass in mechanical machining

An in-depth understanding of material cutting deformation forms the foundation for manufacturing Zirconium-based bulk metallic glass (Zr-based BMG) parts. This study explores the transition in chip segmentation mode from shear slip to shear fracture in Zr-based BMG during mechanical machining. The investigation covers chip micromorphology, cyclic cutting force, machined surface quality, and the themo-mechanical properties under various chip segmentation modes linked to cutting conditions. A size-dependent transition in chip segmentation has been observed in the cutting of Zr-based BMG. At a specific cutting speed, a smaller uncut chip thickness favors chip formation via shear slip, resulting in a smooth primary shear zone (PSZ). Conversely, a larger uncut chip thickness leads to chip shear fracture, with the PSZ displaying fishbone-like and dimple patterns. The integration of the modified cutting kinematic model with the free volume-dependent shear transformation zone (STZ) model suggests that the transition from shear slip to fracture is due to an increase in uncut chip thickness, which causes a greater STZ volume in the PSZ. When the STZ volume surpasses a threshold, the intrinsic structural recovery of material from shearing cannot fully compensate for the free volume softening, leading to excessive free volume that ultimately triggers shear fracture. During the chip shear fracture process, the evolution from fishbone-like patterns to dimples in the PSZ is attributed to faster crack propagation at greater uncut chip thickness or higher cutting speeds. In practical applications, it is advisable to avoid chip shear fracture during machining to maintain high-quality machined surface quality.

Comparative analysis of nanoindentation-induced incipient deformation of zirconium-based bulk metallic glass in various structural states

The incipient plastic deformation behaviour of as-cast and annealed samples of Zr50Cu40Al10 (atom %) bulk metallic glass was investigated by nanoindentation. A validated load-over-displacement versus displacement plot showed the existence of a precursor event to incipient plasticity in both samples. The activation stress remained consistent in both samples, indicating that the event corresponds to local behaviour in regions with the same energy state, and it is not influenced by the overall microstructure. Conversely, the first serration detected in the as-relaxed sample exhibited a greater magnitude, potentially arising from a distinct energy-dissipation rate related to larger-scale microstructural characteristics.

Adhesive wear mechanism of coated tools and its influence on cutting performance during machining of Zr-based bulk metallic glass

Adhesive wear is the primary failure form of coated tools in zirconium-based bulk metallic glasses (Zr-based BMGs) machining. This work investigated the adhesion formation and failure of TiN/Al2O3/Ti(C,N), Al2O3/Ti(C,N), and TiAlN-coated tools when machining Zr41.2Ti13.8Cu10Ni12.5Be22.5 BMG. Characterization of tool-chip interfacial material responses revealed the mechanism of adhesive wear. The relationship between the wear resistance and micro-mechanical properties of coatings was established. The cutting performance of coated tools is also discussed. According to the results, the adhesive wear of coated tools results because the temperature at the tool-chip interface is above the glass transition temperature, reducing the viscosity of chips. Low-viscosity chips were welded to the tool surface under high pressure. Subsequently, high interfacial friction tore the adhesive interface, causing coatings to peel off layer by layer. The exposed tool substrate also generated secondary adhesion, which triggered the diffusion of tungsten and cobalt atoms towards the chip. This was accompanied by redox reactions that exacerbated tool failure. The wear resistance of coatings depended on the elastic modulus (E) and the ratio of nano hardness to elastic modulus (H/E). The TiAlN coating had a lower E of ∼410 GPa and higher H/E of 0.064, and it exhibited better wear resistance than the TiN/Al2O3/Ti(C,N) (E ∼ 436 GPa, H/E = 0.051) and Al2O3/Ti(C,N) (E ∼ 469 GPa, H/E = 0.061) coatings. The lifespan of the TiAlN-coated tool was more than three times longer that of the other two, and the obtained machined surface roughness was less than half that of the others.

Improve plasticity of Zr-based metallic glass by surface treatment

Zirconium-based bulk metallic glasses (BMGs) have received considerable attention due to their high strength and good corrosion resistance. However, the poor plasticity hindered its engineering application. In this paper, we utilized the surface treatment to produce regions with alternate softness and hardness, leading to a noteworthy enhancement in the mechanical performance and corrosion behavior of the material. The results indicate that local distortion significantly improves the compressive fracture strength of the Zr52.5Cu17.9Ni14.6Al10Ti5 amorphous alloy, which increased from 1599 MPa to 1924 MPa, as well as its plasticity, which increased from 1.67% to 15.45%. Furthermore, electrochemical analysis of the imprinted alloy showed improved passivation ability, although its corrosion resistance in a 3.5% solution was inferior. These findings are likely due to material densification after imprinting, along with the increased density of passive films. This study offers new insights and solutions for the industrial application of BMGs based on zirconium.

Thermodynamics and corrosion properties of nitrogen doped zirconium-based bulk metallic glasses

The effect of adding N on the thermodynamics and corrosion resistance of as-cast Zr55Cu30Ni5Al10 bulk metallic glass (BMG) is clarified using electrochemical measurements, microstructure characterization and surface analyses. Compared with Zr55Cu30Ni5Al10 BMG, Nitrogen-doped (Zr55Cu30Ni5Al10)98.5N1.5 BMG is easier to nucleate during heating, but the nucleation growth process becomes more difficult. The corrosion potential (Ecorr) of (Zr55Cu30Ni5Al10)98.5N1.5 BMG and Zr55Cu30Ni5Al10 BMG is −0.32 V and −0.39 V respectively, and the corrosion current density (Icorr) of (Zr55Cu30Ni5Al10)98.5N1.5 BMG and Zr55Cu30Ni5Al10 BMG is 7.90 × 10−8 A/cm2 and 9.13 × 10−5 A/cm2, respectively. I.e., after nitrogen doping the corrosion potential increased slightly, but the corrosion current density decreased by about three orders of magnitude. Meanwhile the oxide film resistance increased significantly, and the surface corrosion diffusion effect weakened. Nitrogen reduces the H+ concentration in the pitting pits, slows down the pitting rate, and improves the corrosion resistance. Proper nitrogen can improve the thermal-stability and surface corrosion resistance of Zr-based BMGs.

Fabrication of antibacterial Zr-BMG biomimetic surfaces by femtosecond laser

Zirconium-based bulk metallic glasses (Zr-BMGs) are ideal materials for medical devices due to their unique amorphous structure, excellent wear resistance, good corrosion resistance, and high specific strength. The antibacterial performance of medical devices is critical in clinical treatments. Biomimetic structures are shown to have good antifouling behavior on the material's surface. In this study, six types of biomimetic structures (Shark skin-like, Rose leaf-like, Nepenthes-like, Rice leaves-like, Butterfly wing-like, and Bamboo leaf-like) were constructed on Zirconium based bulk metallic glass by femtosecond laser with different laser energy intensities. The crystallization behavior and bacterial adhesion properties of biomimetic surfaces modified with femtosecond laser were explored. The results show that biomimetic surfaces have better antifouling characteristics than polished surfaces. While the antifouling properties of rice leaf-like structure and butterfly wing-like structure were the most effective. However, the bactericidal performance of the shark skin-like structure was the best. Furthermore, crystallization was observed on the Shark skin-like and Rose leaf-like surfaces processed with laser energy intensities greater than 2.38 J/mm2. Despite the surface crystallized layer, the substrate was still amorphous. Finally, based on the surface in vitro and in vivo cytotoxicity evaluation, the Nepenthes-like structure covered with disordered nano bulges showed the best balance between antifouling, bactericidal, and biocompatibility. The laser fabricated biomimetic structures can improve the antibacterial activity of Zr-BMG surgical tools and orthopedic implants, thus improving medical treatment quality.

Plasma electrolytic polishing for improving the surface quality of zirconium-based bulk metallic glass

Plasma electrolytic polishing for improving the surface quality of zirconium-based bulk metallic glass

Effects of periodic surface structures induced by femtosecond laser irradiation on the antibacterial properties of Zr-based amorphous material

ObjectiveIn this essay, a femtosecond laser is used to create various structures on the surface of Zr-based amorphous material. MethodsThrough the raster scan mode, under different laser energy densities, LIPSS (Laser-induced periodic surface structures), SWPSS (Super-wavelength periodic surface structure) and microporous structures were obtained in the experiment. Various surface properties of the micro-nano structures were tested. ResultExperimental results illuminate that laser energy fluence is the key to determining the formation of nano- and microscale structures. The laser treatment greatly improves the surface roughness of the sample. The laser texture converts the originally hydrophilic specimen surface into a hydrophobic surface, which greatly reduces the material's surface energy. We found that all the formed surface structures can reduce the adhesion of Escherichia coli and Staphylococcus aureus. In detail, the adhesion rate of bacteria on the surface of SWPSS is the lowest. ConclusionThis article comprehensively discusses the influence mechanism of nano- and microscale structures on bacterial adhesion from four aspects: surface roughness, hydrophobicity, surface energy, and surface morphology. The study manifest that the period and amplitude of the nano- and microscale structures are the keys to bacterial adhesion. In addition, experiments have shown that nano- and microscale structures can effectively improve the corrosion resistance of zirconium-based bulk metallic glass.

Effect of speed ratio on shear angle and forces in elliptical vibration assisted machining

Elliptical vibration-assisted machining (EVAM) has been employed in manufacturing industries to improve the machining performance of metal alloys. The mechanics of EVAM is dependent on the critical process parameters, including the horizontal speed ratio (HSR) defined as the ratio between the original cutting speed and the horizontal vibration speed. This paper presents a new mechanics model of EVAM, which reveals that the primary reason for shear angle variation at different HSR values is the strain-hardening property of the workpiece material instead of the friction reversal phenomenon. The model quantitatively determines the effect of the HSR on the shear angle, friction reversal, and instantaneous cutting forces in EVAM. A 2-D vibration assistance stage driven is developed to perform EVAM experiments on aluminum alloy with evident strain-hardening property and Zirconium-based bulk metallic glass that is less sensitive to strain-hardening. The chip morphology is examined at various speed ratios and uncut chip thicknesses to validate the shear angle prediction from the mechanics model. In addition, the model predicts the time instance corresponding to the friction reversal, which is also dependent on the shear angle and HSR in EVAM. Finite element simulations are performed to validate the predicted instantaneous cutting forces and friction reversal from the analytical mechanics model.

Using Cu as a Spacer to Fabricate and Control the Porosity of Titanium Zirconium Based Bulk Metallic Glass Foams for Orthopedic Implant Applications.

In this study, a porous titanium zirconium (TiZr)-based bulk metallic foam was successfully fabricated using the Cu spacer by employing the hot press method. TiZr-based bulk metallic foams with porosities ranging from 0% to 50% were fabricated and analyzed. The results indicate that thermal conductivity increased with the addition of Cu spacer; the increased thermal conductivity reduced the holding time in the hot press method. Moreover, the compressive strength decreased from 1261 to 76 MPa when the porosity of the TiZr-based bulk metallic foam increased to 50%, and the compressive strength was predictable. In addition, the foam demonstrated favorable biocompatibility in cell viability, cell migration capacity, and calcium deposition tests. Moreover, the pore size of the porous TiZr-based bulk metallic foam was around 120 µm. In conclusion, TiZr-based bulk metallic foam has favorable biocompatibility, mechanical property controllability, and porous structure for bone ingrowth and subsequent enhanced osteointegration. This porous TiZr-based bulk metallic foam has great potential as an orthopedic implant to enhance bone healing and decrease healing time.

Amorphous-Crystalline Composite Microstructure Formation in Zr<sub>46</sub>Cu<sub>46</sub>Al<sub>8</sub> Alloy at the Conditions of Selective Laser Melting

Amorphous alloys are promising structural materials because of their high mechanical strength. Their drawbacks are low ductility and severe size restrictions for components obtained by casting. Additive manufacturing by selective laser melting (SLM) consists in successive fusion of small portions of material to add to a growing part. Each portion is subjected to a short thermal cycle favorable for amorphization. Thus, one can build an amorphous part as large as necessary. We study the microstructure of cast samples of a zirconium-based bulk metallic glass after laser processing with the parameters typical for SLM. Scanning electronic microscopy has shown partial crystallization in the heat affected zone of the laser beam. The spatial distribution and the volume fraction of the crystalline phase can be controlled by laser processing parameters. The obtained amorphous-crystalline structures are promising to increase the ductility of bulk metallic glasses.

Antibacterial Performance of Zr-BMG, Stainless Steel, and Titanium Alloy with Laser-Induced Periodic Surface Structures.

A laser-induced periodic surface structure (LIPSS) was shown to have antibacterial adhesion properties in previous research. In this study, the antibacterial performance of LIPSS on traditional biometals (stainless steel and titanium alloy) and a potential biometal (zirconium-based bulk metallic glass, Zr-BMG) was investigated. A femtosecond laser was used to fabricate LIPSS on the specimens. Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) were used to examine the antibacterial behavior of the LIPSS samples. The bacterial adhesion force on each specimen was evaluated by an atomic force microscopy (AFM) cell probe. The results showed that the LIPSS on all three metal surfaces significantly lowered antibacterial adhesion compared to polished metal specimens. E. coli demonstrated a higher adhesion force but a lower surface adhesion rate compared to S. aureus. The Zr-BMG specimen with LIPSS has multiple antimicrobial mechanisms (physical antiadhesion and chemical elimination), while the traditional biometals (316L and TC4) mainly offer physical antiadhesion. Finally, an in vitro/vivo study showed that specimens with LIPSS surfaces did not significantly affect the biocompatibility of the specimens. This study reveals that the Zr-BMG specimen with femtosecond laser-processed LIPSS is an ideal choice for achieving an antibacterial surface.

Study on tribological characteristics of Zr-based BMG via nanoscratch techniques

This study aims at investigating tribological characteristics of zirconium-based bulk metallic glass (BMG) using nanoindentation and nanoscratch techniques. The nanomechanical properties of Zr65Cu15Al10Ni10 (at. %, Zr-based BMG) are first assessed via nanoindentation tests and simulations. The tribological performance of Zr-based BMG under various scratch conditions are investigated via nanoscratch tests with multiple ramp and constant normal loads. It is found that coefficient of friction (COF) irregularly increases with normal load due to the formation of fracture and chipping, which play crucial roles on the frictional behaviors of Zr-based BMG. The critical load for fracture and chipping formation is identified for the considered test conditions. Wear mechanism of Zr-based BMG under nanoscratching are investigated by observing the morphologies of scratch tracks through scanning electron microscope (SEM). The findings of this study can be beneficial for tailoring the surface of Zr-based BMG by using micro-machining and patterning techniques.

Effect of cutting speed on surface integrity and chip formation in micro-cutting of Zr-based bulk metallic glass

Single-shear plane theory is an effective tool for understanding the cutting mechanisms of conventional and precision machining. This study investigates the formation of multiple shear bands in micro-cutting of zirconium-based bulk metallic glass (BMG) where classic models have not been studied. A series of slip steps were observed in the cutting direction which was significantly affected by cutting speed. Surface roughness of the machined surface in micro-cutting BMG was found to be sensitive to the cutting speed. Electron microscopy studies further confirmed the mechanism of the micro-cutting-induced nanocrystallization with the formation of shear bands within the primary deformation zone in the micro-cutting process under various cutting speeds. This work contributes to demonstrating the effects of cutting speed on the formation of the shear band and the serrated flow behavior under complex loading and boundary conditions in micro-cutting.

Oxygen effect on bending behavior of a zirconium based bulk metallic glass

In this work we report a systematic study regarding the effect of different oxygen contents (150 – 2000 wppm) on the microstructure and mechanical properties of the commercial bulk metallic glass Vitreloy® 106a (Zr58.5Nb2.8Cu15.6Ni12.8Al10.3). Scanning electron microscopy (SEM) analyses and Synchrotron X-ray diffraction patterns have confirmed the presence of crystalline precipitates dispersed in the amorphous matrix for samples contaminated with more than 900 wppm of oxygen. Three-point bending tests and fracture surface SEM investigations have shown that the brittle phases formed combined with the oxygen contamination of the matrix resulted in a significative fracture resistance reduction as well as ductility loss following the increase of oxygen content.

Reduced bacterial adhesion on zirconium-based bulk metallic glasses by femtosecond laser nanostructuring.

As high-performing materials, bulk metallic glasses have attracted widespread attention for biomedical applications. Herein, the bacterial adhesion properties of femtosecond laser-nanostructured surfaces of four types of zirconium-based bulk metallic glasses are assessed. Laser-induced periodical surface structures and nanoparticle structures were fabricated by femtosecond laser irradiation under different energy intensities (0.23 and 2.3 J/mm2). Surface topography, roughness, wettability, and surface energy were investigated after femtosecond laser irradiation and the surface bacterial adhesion properties were explored using Escherichia coli and Staphylococcus aureus as respective representatives of Gram-negative and Gram-positive bacteria. 4',6-Diamidino-2-phenylindole fluorescence staining was used to characterize and assess the bacterial surface coverage rate. The in vitro cytotoxicity of polished and laser-nanostructured surfaces was investigated using MC3T3-E cells. The obtained results demonstrate that femtosecond laser surface nanostructuring retained the amorphous structure of zirconium-based bulk metallic glasses and led to an obvious decrease in bacterial adhesion compared with polished surfaces. The inhibition of bacterial adhesion on laser-induced periodical surface structures was greater than on nanostructured surfaces after 24 h of bacterial incubation. In addition, femtosecond laser nanostructuring did not have an apparent effect on the cytotoxicity of zirconium-based bulk metallic glasses.

Nanoindentation of zirconium based bulk metallic glass and its nanomechanical properties

Nanoindentation experiments with a Berkovich tip are performed on zirconium based bulk metallic glass (Zr-BMG, Zr65Cu15Al10Ni10) to study its deformation and mechanical properties (elastic modulus and hardness) at nanoscale. Further to reveal indentation-size effect (ISE), the influence of loading rate and peak and cyclic loads on evaluated nanomechanical properties are investigated in detail. The loading rate has significant effect on serration flow (pop-in), which gets predominant at higher loads. According to the Oliver-Pharr method, hardness becomes peak load-independent, whereas elastic modulus increases with the load. The same phenomenon is observed with sinus and progressive multicycle indentation methods. However, observation of significant pile-up (the ratio of elastic and total energy We/Wt ≈ 0.33 < 0.5) questions the application of the Oliver-Pharr method to Zr-BMG; therefore, evaluated nanomechanical properties are corrected with the projected contact area measured by atomic force microscopic (AFM) and finite element analysis to reduce ISE.

Experimental study on wire-electrical discharge machining of zirconium-based metallic glass

In this paper, the new alloy material, zirconium-based bulk metallic glass (Zr41.2Ti13.8Cu12.5Ni10Be22.5), which is hard and brittle, was the research object. Since the process of wire-electrical discharge machining offers the advantage of processing hard and brittle conductive materials, the effects of discharge parameters on material removal rate, surface roughness, surface morphology, carbonization and crystallization have been studied by changing discharge voltage, peak current and pulse width. The results showed that material removal rate and surface roughness increased with the increase of peak current and pulse width. Compared to peak current and pulse width, voltage exerted a less influence on material removal rate and surface roughness. The surface of the workpiece after processing presented fish-scale structure with some bumps, microspheres and droplets. As the discharge energy increased, more carbon deposits from cutting fluid were deposited on the surface of the workpiece, resulting in an increase of the carbon content which accelerated surface carbonization. The workpiece processed by low discharge energy kept a good amorphous state, but its surface layer had a tendency to crystallize. Furthermore, with the increase of discharge energy, sharp diffraction peaks began to appear, and crystallization occurred. Based on the current inadequacy of research on wire-electrical discharge machining of zirconium-based metallic glass, the purpose of this study is to provide a reference for further research on wire-electrical discharge machining of zirconium-based metallic glass.

Bioinspired nacre-like alumina with a bulk-metallic glass-forming alloy as a compliant phase

Bioinspired ceramics with micron-scale ceramic “bricks” bonded by a metallic “mortar” are projected to result in higher strength and toughness ceramics, but their processing is challenging as metals do not typically wet ceramics. To resolve this issue, we made alumina structures using rapid pressureless infiltration of a zirconium-based bulk-metallic glass mortar that reactively wets the surface of freeze-cast alumina preforms. The mechanical properties of the resulting Al2O3 with a glass-forming compliant-phase change with infiltration temperature and ceramic content, leading to a trade-off between flexural strength (varying from 89 to 800 MPa) and fracture toughness (varying from 4 to more than 9 MPa·m½). The high toughness levels are attributed to brick pull-out and crack deflection along the ceramic/metal interfaces. Since these mechanisms are enabled by interfacial failure rather than failure within the metallic mortar, the potential for optimizing these bioinspired materials for damage tolerance has still not been fully realized.