Search Results (84)

In the present investigation, high stability Vitreloy Zr₄₄Ti₁₁Cu₁₀Ni₁₀Be₂₅ bulk metallic glass has been subjected to severe shear deformation by high-pressure torsion for 0.1 revolutions under an applied pressure of 4 and 8 GPa. The fully glassy nature of the as-cast glass has been confirmed by X-ray powder diffraction and differential scanning calorimetry. Deformation-induced surface features on an internal plane of the deformed disk-shaped specimens were studied in detail at the macroscopic level by optical reconstruction method and at microscopic scales by white-light optical profilometry. Shear and compressive strain components were measured based on surface changes and it was determined that compressive strain gradient with 0.2–0.4 strain change builds up toward the disk edge, while only part of the nominal shear deformation occurs in the disk interior. The effect of strain localization in the Vitreloy bulk metallic glasses has been quantified by a surface distortion model based on simple shear. The model was then validated experimentally by the reconstructed z-profiles. Full article

The effects of a small addition of Ag and Ti on the thermal stability, mechanical properties, and tribological behavior of Zr-Co-Al bulk metallic glass (BMG) were investigated. A 5 at.% addition of Ag and Ti to the Zr-Co-Al base alloy improved the thermal stability and had no significant effect on the mechanical properties but considerably improved the wear behavior. The coefficient of friction decreased while the wear rate increased with increasing normal loads for all three alloys. Zr-Co-Al-Ti showed the best tribological performance among the studied alloys, with coefficient of friction and wear rate lower by a factor of four compared to Zr-Co-Al BMG. Predominantly oxidative wear was seen for the quaternary Zr-Co-Al-Ag and Zr-Co-Al-Ti BMGs at higher loads in contrast to abrasive and adhesive wear for the ternary Zr-Co-Al base alloy. These results highlight the potential of Ag and Ti micro-alloying for improving the mechanical and tribological properties of Zr-based amorphous alloys. Full article

Ti-based bulk metallic glass composites (BMGMCs) containing an in situ formed metastable β phase normally exhibit enhanced plasticity attributed to induced phase transformation or twinning. However, the underlying deformation micromechanism remains controversial. This study investigates a novel deformation mechanism of Ti-based BMGMCs with a composition of Ti_42.3Zr₂₈Cu_8.3Nb_4.7Ni_1.7Be₁₅ (at%). The microstructures after tension were analyzed using advanced electron microscopy. The dendrites were homogeneously distributed in the glassy matrix with a volume fraction of 55 ± 2% and a size of 1~5 μm. The BMGMCs deformed in a serrated manner with a fracture strength (σ_f) of ~1710 MPa and a fracture strain of ~7.1%, accompanying strain hardening. The plastic deformation beyond yielding was achieved by a synergistic action, which includes shear banding, localized amorphization and a localized BCC (β-Ti) to HCP (α-Ti) structural transition. The localized amorphization was caused by high local strain rates during shear band extension from the amorphous matrix to the crystalline reinforcements. The localized structural transition from BCC to HCP resulted from accumulating concentrated stress during deformation. The synergistic action enriches our understanding of the deformation mechanism of Ti-based BMGMCs and also sheds light on material design and performance improvement. Full article

The effects of partially substituting Al for Cu in Zr_59.62Cu_18.4-xNi₁₂Al_6+xNb₃Hf_0.78Y_0.2 (x = 0, 2, 4, 6, 8 at.%) bulk metallic glasses (BMGs) on their glass-forming ability (GFA), quasi-static and dynamic mechanical properties, and energy characteristics were investigated. The results showed that an appropriate substitution of Al for Cu can improve GFA and reach a critical casting size up to 10 mm. Additionally, with Al replacement of Cu, the change in the distribution and content of free volume inside the BMGs was the main reason for the quasi-static compression plasticity. In contrast, the BMGs exhibited no plasticity during dynamic compression and high-speed impact, owing to the short loading time and thermal softening effect. In terms of energy characteristics, all alloys have a high combustion enthalpy. And on the surface of the fragments collected from impact, the active elements Zr, Al, and Nb reacted because of the adiabatic temperature rise. Further, x = 4 at.% Zr-based BMG with its superior overall performance could penetrate a 6 mm Q235 plate at a speed of 1038 m/s, combining excellent mechanical properties and energy characteristics. This study contributes to the development of Zr-based BMGs as novel energetic structural materials. Full article

Enhanced plasticity is obtained in a structurally rejuvenated Zr-based bulk metallic glass (BMG) that has been treated via cryogenic thermal cycling (CTC) for one hundred cycles. More than one primary shear band is activated due to the structural rejuvenation, which can inhibit the jerky and system-spanning propagation of shear bands to generate sluggish shear-dynamics. These are mapped to the slip statistics, including the decreased critical avalanche size, the much longer avalanche duration of large (system-spanning) slips, and a great number of small avalanches. Moreover, the universal scaling of slip avalanches for three applied stress ranges is addressed to predict the applied stress at which the failure avalanche appears most. These results indicate that slip statistics can be the fingerprints to show how much the BMG is rejuvenated, and the failure avalanche provides a good opportunity to intervene in the failure of BMGs in advance. Full article

In this study, a novel crawler-type continuous casting (CC) technology was designed to efficiently and cost-effectively produce bulk metallic glass (BMG) slabs. As a crucial process parameter, casting temperature has a significant impact on the operation of CC devices and the quality of slabs. CC experiments of the Zr_41.2Ti_13.8Cu_12.5Ni_10.0Be_22.5 (Vit1) BMG slab were carried out at the casting temperatures of 1073 K, 1123 K, and 1173 K, and the microstructure and properties of slab samples were analyzed and studied. The experimental results indicate that the BMG slabs can be prepared by CC at 1173 K and 1123 K. When the temperature is reduced to 1073 K, the Be₁₂Ti crystal phase precipitates inside the CC slab, which has a certain impact on the thermal stability and compressive performance of the slab. The control of casting temperature does not affect the glass-forming ability (GFA) of the slab in the CC process. Full article

Bulk metallic glasses are modern engineering materials with unique functional properties. Zr-based alloys are particularly attractive as they exhibit high glass forming ability as well as good mechanical properties. Due to their relatively high thermal stability, reaching as much as 400 °C, they can be surface-treated in low-temperature plasma to further improve their mechanical properties. The subject of this study was to determine the influence of the technological parameters of nitriding in low-temperature plasma on the structure and mechanical properties of Zr₄₈Cu₃₆Al₈Ag₈ bulk metallic glass. In the course of this study, the influence of the ion accelerating voltage on the structure and micromechanical properties of the bulk metallic glass was analyzed. The produced samples were characterized in terms of nanohardness, layer adhesion by using the scratch test, and wear resistance by using the ball-on-disc method. As a result of low-temperature plasma nitriding, a significant increase in the surface nanohardness of the Zr₄₈Cu₃₆Al₈Ag₈ bulk metallic glass was obtained. The produced layers exhibited high adhesion to the substrate and they improved the wear resistance of the glass. The present study indicates the possibility of modifying the surface properties of bulk metallic glasses by using diffusion processes in low-temperature plasma without substrate crystallization. Full article

A series of Ti₄₁Zr₂₅Be_34-xNi_x (x = 4, 6, 8, 10 at.%) and Ti₄₁Zr₂₅Be_34-xCu_x (x = 4, 6, 8 at.%) bulk metallic glasses were investigated to examine the influence of Ni and Cu content on the viscosity, thermoplastic formability, and nanoindentation of Ti-based bulk metallic glasses. The results demonstrate that Ti₄₁Zr₂₅Be₃₀Ni₄ and Ti₄₁Zr₂₅Be₂₆Cu₈ amorphous alloys have superior thermoplastic formability among the Ti₄₁Zr₂₅Be_34-xNi_x and Ti₄₁Zr₂₅Be_34-xCu_x amorphous alloys due to their low viscosity in the supercooled liquid region and wider supercooled liquid region. The hardness and modulus exhibit obvious variations with increasing Ni and Cu content in Ti-based bulk metallic glasses, which can be attributed to alterations in atomic density. Optimal amounts of Ni and Cu in Ti-based bulk metallic glasses enhance thermoplastic formability and mechanical properties. The influence of Ni and Cu content on the hardness of Ti-based bulk metallic glasses is discussed from the perspective of the mean atomic distance. Full article

Ti-based bulk metallic glasses are promising materials for metallic bone implants, mainly due to their mechanical biofunctionality. A major drawback is their limited corrosion resistance, with high sensitivity to pitting. Thus, effective surface treatments for these alloys must be developed. This work investigates the electrochemical treatment feasibility of nitric acid (HNO₃) solution for two bulk glass-forming alloys. The surface states obtained at different anodic potentials are characterized with electron microscopy and Auger electron spectroscopy. The corrosion behavior of the treated glassy alloys is analyzed via comparison to non-treated states in phosphate-buffered saline solution (PBS) at 37 °C. For the glassy Ti₄₇Zr_7.5Cu₃₈Fe_2.5Sn₂Si₁Ag₂ alloy, the pre-treatment causes pseudo-dealloying, with a transformation from naturally passivated surfaces to Ti- and Zr-oxide nanoporous layers and Cu-species removal from the near-surface regions. This results in effective suppression of chloride-induced pitting in PBS. The glassy Ti₄₀Zr₁₀Cu₃₄Pd₁₄Sn₂ alloy shows lower free corrosion activity in HNO₃ and PBS due to Pd stabilizing its strong passivity. However, this alloy undergoes pitting under anodic conditions. Surface pre-treatment results in Cu depletion but causes enrichment of Pd species and non-homogeneous surface oxidation. Therefore, for this glassy alloy, pitting cannot be completely inhibited in PBS. Concluding, anodic treatments in HNO₃ are more suitable for Pd-free glassy Ti-based alloys. Full article

Zr₅₇Cu₁₅Ni₁₀Nb₅ (more known as Vit-106) is a promising zirconium-based alloy with a high glass-forming ability, and belongs to the so-called bulk metallic glasses (BMG). Workpieces with a size of around one centimeter in all three dimensions can be obtained from a BMG alloy by casting. However, further increasing the cast size decreases the cooling rate and thus induces crystallization. Selective laser melting (SLM) is a well-known technique to overcome size limitations for BMGs because a workpiece is built by the addition of multiple melt portions in which the cooling rate is kept above the critical one. Currently, BMG parts obtained by SLM suffer from partial crystallization. The present work studies the influence of SLM process parameters on the partial crystallization of Vit-106 by metallography and the influence of the microstructure on mechanical properties by microhardness and wear resistance testing. Submicron crystalline inclusions are observed in an amorphous matrix of a Vit-106 alloy obtained by SLM. The size and the concentration of the inclusions can be controlled by varying the laser scanning speed. It is shown that submicron crystalline inclusions formed in the amorphous matrix during SLM can favorably affect microhardness and wear resistance. Full article

Photocatalysis is an energy-saving and high-efficiency green environmental technology. Because of its wide band gap and low light utilization, few studies have been conducted on ZrO₂ used as a photocatalytic material. In this paper, a corrosion-resistant superhydrophobic ZrO₂ coating was prepared on the surface of Zr-based bulk metallic glass by electrochemical etching. This coating not only showed a better corrosion resistance and easier collection, but also presented a stable degradation performance when combined with H₂O₂; these characteristics are necessary for photocatalysts to survive under harsh environments. This study provides a new direction for designing superhydrophobic surfaces on bulk metallic glass that possess a functional performance. Full article

In this paper, the partially crystallized Zr₇₀Cu_13.5Ni_8.5Al₈ bulk metallic glasses (BMGs) were prepared, and their superplastic deformation ability in the supercooled liquid region was studied via compression over a wide range of strain rates from 5 × 10⁻⁴ s⁻¹ to 1 × 10⁻² s⁻¹. It has been found that the superplastic deformation behavior of the BMGs is strongly dependent on the strain rate and temperature. The flow behavior of the BMGs transformed from Newtonian fluid to non-Newtonian fluid with the increase in the strain rate and the decrease in temperature. Based on the high-temperature compression results, a thermalplastic forming map was constructed, and the optimal superplastic forming parameters were obtained. Then, gears were successfully extruded using part of the optimal thermal processing parameters. Further studies showed that high-temperature extrusion induced the crystallization of the BMGs, which increased the microhardness of the gears. Full article

Zr-based bulk metallic glasses (BMGs) have many unique properties. Due to their excellent performance and manufacturing process, they have become a research focus in the material science community. Electrolyte Jet Machining (EJM) is a non-contact electrochemical processing method with high surface integrity and high material removal rate (MRR). In this research, the sub-millimeter channels fabricated by EJM on Zr-based BMGs have been studied to explore the dissolution mechanisms and surface integrity under different scanning rates and voltages. The results show that, with other machining parameters holding constant, an increase in voltage leads to a substantial enhancement in both the depth and width of the channels machined on Zr-based BMGs. Notably, the influence of voltage on the depth of the channels is particularly pronounced. Additionally, an escalation in scanning rate correlates with a decrease in channel depth, with minimal variation in channel width. This study indicates that alcohol-based EJM is an effective method to fabricate sub-millimeter channels and modulate structures on Zr-based BMGs. Full article

Zr-based bulk metallic glasses (BMGs) possess unique mechanical and biochemical properties, which have been widely noticed. Jet electrochemical machining (jet-ECM), characterized by a high-speed jet, is a non-contact subtractive method with a high resolution and a high material removal rate (MRR). Past work on the electropolishing of Zr-based BMGs has indicated the feasibility of the NaCl-Ethylene Glycol (EG) electrolyte. In this research, the jet-ECM of Zr-based BMGs in the NaCl-EG electrolyte was studied to explore the dissolving mechanisms and surface integrity according to the voltage, pulse-on time and effective voltage time. The diameter, depth and surface morphologies of dimples were evaluated. The results showed that using this alcohol-based electrolyte led to a desirable surface morphology. The diameter and depth of the dimples varied with the voltage and the effective voltage time in a significantly positive proportional manner. Additionally, cases based on multiple parameter sets exhibited different stray corrosion severity. Afterward, machining performance can be enhanced in the next stage by tuning machining parameters to obtain microscale dimples with better quality. Full article

Ti-based metallic glasses have a high potential for implant applications. The feasibility of a new biocompatible Ti-based bulk metallic glass composite for selective laser melting (SLM) had been examined. Therefore, it is necessary to design a high-glass-forming-ability Ti-based metallic glass (∆T_x = 81 K, γ = 0.427, γ_m = 0.763), to fabricate a partial glass-formable spherical powder (the volume fraction of the amorphous phase in the atomized Ti-based powders being 73% [size < 25 μm], 61% [25–37 μm], and 50% [37–44 μm]), and establish an SLM parameter (a scan rate of 600 mm/s, a power of 120 W, and an overlap of 10%). The Ti₄₂Zr₃₅Si₅Co_12.5Sn_2.5Ta₃ bulk metallic glass composite was successfully fabricated through SLM. This study demonstrates that the TiZrSiCoSnTa system constitutes a promising basis for the additive manufacturing process in terms of preparing biocompatible metallic glass composites into complicated graded foam shapes. Full article