Search

The effect of Fe-C alloy additions on thermal, mechanical and corrosive properties of (Cu50Zr40Ti10)1-x(Fe-C)x (x = 0–2.20 at%) alloys were systematically investigated. The results show that the Fe and C additions can enhance glass transition temperature Tg and onset crystallization temperature Tx, but narrow supercooled liquid region ΔTx. Work-hardening can be clearly observed for the Cu-based bulk metallic glasses (BMGs) containing Fe and C elements. The yield strength (σy), fracture strength (σf) and plastic strain (ep) are drastically increased by Fe-C alloy additions. The corrosion potential Ec increases and the corrosion current density ic decreases with increasing Fe and C contents. The studied Cu-based BMGs exhibit unique and novel anodic polarization behavior characterized by current platforms plus current serrations. The current serrations are much larger for the Cu-based BMGs with 0 ≤ x ≤ 1.32 at% than for those with 1.76 ≤ x ≤ 2.20 at%. The corrosion surface images are changed from the pits to the passive films by Fe-C alloy additions. The corrosion behavior gradually transforms from the pitting corrosion to the self-passivization with increasing Fe and C contents. The corresponding mechanisms are also discussed.

(Cu50Zr50)x(Cu73Ti27)100-x (x = 0.63–0.75 at.%) alloys are designed using the proportional mixing of Cu50Zr50 and Cu73Ti27 binary alloys. Their thermal, mechanical and corrosive properties as well as the glass forming ability (GFA) are systematically investigated. The results show that the studied Cu-based glass forming alloys are bulk metallic glass composites (BMGCs) with off-eutectic compositions and display work-hardening behavior. The glass transition temperature and the reduced glass transition temperature increase and then decrease with increasing x when x ≥ 0.74 at%, while on the contrary for the critical cooling rate and supercooled liquid region. Both yield strength and fracture strength firstly increase and then decrease with decreasing x when x ≤ 0.71 at%. The plastic strain of (Cu50Zr50)0.75(Cu73Ti27)0.25 BMGC is the largest among the studied Cu-based BMGCs. Potentiodynamic polarization measurements show that all studied BMGCs exhibit a step-like anodic polarization behavior, indicating two competitive procedures of pitting corrosion and self-passivization. The corrosion behavior gradually transforms from predominant self-passivization to the pitting corrosion with decreasing x. Both corrosion current density and onset passive current density of (Cu50Zr50)0.75(Cu73Ti27)0.25 BMGCs are two orders of magnitude lower than those of the other Cu-based BMGCs. The mechanisms for the GFA and the corrosion are also discussed. The present work would shed light on how to design and develop BMGCs with superior comprehensive performances.

The intrinsic heterogeneities of the metallic glasses can be activated through cryogenic thermal cycling, making irreversible structural changes after the treatment and inducing rejuvenation to the materials. Although the energy rise after cryogenic thermal cycling can be easily determined from calorimetry, the energy change made by the heterogeneities is unknown because of the difficulty in witnessing these heterogeneities. In this paper, we investigated the changes of a typical heterogeneity: the Fe3Si crystallite, embedded in two partially-crystallized Fe-based metallic glasses, and subsequently deduced its influence on the neighbouring glassy matrix. It was found that even in the initial, partially-crystallized alloys, the Fe3Si nanocrystals were under residual expansion. Furthermore, both expansion and contraction can be detected after cryogenic thermal cycling depending on the applied number of cycles. The maximum residual volumetric strain preserved after CTC is in the order of 0.1%. Moreover, the stored energy of both crystals and glasses are calculated and the total energy rise is determined at the order of 5–50 mJ/g. The study of partially-crystallized alloys not only provides a useful model of heterogeneous materials but also reflects the structural change of the glassy phases, making this method attractive in understanding the effects of thermo-mechanical processing on heterogeneities.

The investigation on the stress relief of magnetic materials is important both for the industrial process and the academic research. In this work, the stress effects on the magnetic characteristics in Fe-based metallic glasses (MGs) are investigated under the applied bending stress and various annealing treatments. It was found that both the magnetic induction intensity B and effective permeability μ′ decrease while coercivity Hc increases with the applied compressive stress, indicating that the compressive effect is dominant on the magnetic characteristics in Fe78Si9B13 MG ribbons. We also found that the wide domain wall movement and the rotation of the narrow domains are seriously affected by internal stress during the magnetization process. Our results reveal that the stress relief plays a critical role in improving magnetic properties of Fe-based MGs and are helpful for understanding the correlations between the stress, microstructure change and magnetic softness in magnetic MGs.

The intrinsic correlation between the fracture morphology evolution and the structural heterogeneity of flow units in a typical Zr 52.5 Ti 5 Cu 17.9 Ni 14.6 Al 10 (vit105) metallic glass (MG) upon annealing was investigated. By systematically tuning the annealing time at temperature below the glass transition temperature, a series of dimple-like fracture morphology were obtained, which is the unique fingerprint-like pattern for every annealing state. Based on the structural relaxation model of flow units, the evolution of the typical dimple sizes, the largest and smallest dimple size, with annealing were well fitted. Then the evolution of flow unit density was estimated from the fracture morphology evolution, which displays the same evolution trend with that measured from thermal relaxation. A stochastic dynamic model considering the interaction of activated flow units was proposed to analyze the effect of the initial flow unit density and the flow unit interaction intensity on the dynamic evolution of dimple distribution. Our work may provide a novel scheme to investigate the structural fingerprint information on flow units from fracture morphology, and enlighten the microscopic structural origin of the ductile-to-brittle transition during structural relaxation in MGs.

(Zr54Al10.2Ni9.4Cu26.4)100−xTix (x = 0–0.5, at%) bulk metallic glasses were prepared by water-cooled copper suction casting method. The Ti microalloying effect on glass forming ability and physical and chemical properties of Zr54Al10.2Ni9.4Cu26.4 glass forming alloy were systematically investigated. The glass forming ability is the largest for the Zr-based alloy with 0.3 at% Ti. The glass transition temperature is decreased by the Ti addition, while the supercooled liquid region is broadened. Both strength and plasticity are significantly enhanced by the Ti addition. The yield strength and the fracture strength firstly increase and then decrease when the Ti content reaches up to 0.3 at%. The plastic strain and the fracture strain increase with increasing Ti content. In addition, the corrosion potential is slightly decreased by the Ti addition. The corrosion current density increases with increasing Ti content. The pitting corrosion becomes increasingly serious with increasing Ti content. The honeycomb corrossion structure can be clearly observed when the Ti content reaches up to 0.5 at%. The corresponding mechanisms are also discussed in detail.

Room-temperature mechanical properties of Cu 50 Zr 40 Ti 10– x Ni x (0≤ x ≤4, mole fraction, %) bulk metallic glasses (BMG) with aspect ratios in the range of 1:1–2.5:1 and loading rates in the range of 1×10 −5 –1×10 −2 s −1 were systematically investigated by room-temperature uniaxial compression test. In the condition of an aspect ratio of 1:1, the superplasticity can be clearly observed for Cu 50 Zr 40 Ti 10 BMG when the loading rate is 1×10 −4 s −1 , while for Cu 50 Zr 40 Ti 10– x Ni x ( x =1–3, mole fraction, %) BMGs when the loading rate is 1×10 −2 s −1 . The plastic strain ( ɛ p ), yielding strength ( σ y ) and fracture strength ( σ f ) of the studied Cu-based BMGs significantly depend on the aspect ratio and the loading rate. In addition, the σ y of the studied Cu-based BMGs with an aspect ratio of 1:1 is close to the σ f of those with the other aspect ratios when the loading rate is 1×10 −2 s −1 . The mechanism for the mechanical response to the loading rate and the aspect ratio was also discussed.

A multicomponent metallic glass (MG) with highly efficient and anomalous durability for catalyzing water splitting is reported. The outstanding performance of the MG catalyst contributed by self-optimized active sites originates from the intrinsic chemical heterogeneity and selective dealloying on the disordered surface; thus, a new mechanism for improving the durability of catalysts is uncovered.

(Zr53Al11.6Ni11.7Cu23.7)1-x(Fe77.1C22.9)x (x = 0–2.2 at.%) bulk metallic glasses (BMGs) were prepared by water cooling copper mold suction casting and their isochronous crystallization characteristics are investigated. The glass transition temperature, crystallization temperature, and crystallization peak temperature for all studied Zr-based BMGs firstly increase with increasing heating rate, and then decrease when the heating rate increases up to 60 K/min for the BMGs (0 ≤ x ≤ 0.88 at.%) and 80 K/min for the BMGs (1.32 ≤ x ≤ 2.20 at.%). The glass transition temperature, crystallization temperature, glass transition activiation energy, crystallization activiation energy, and activiation energy for crystallization peak temperature of the Fe- and C-free Zr-based BMG are the smallest among the studied BMGs, indicating that Fe and C additions are benificial to delaying the glass transition and the crystallization. Fe and C additions influence more significantly on the glass transition than on the crystallization. The local crystallization activiation energy for the Fe- and C-free BMG are the smallest among the studied BMGs, indicating that the crystallization is easy for the Fe- and C-free BMG. The peak height of local Avrami exponent and its corresponding crystallization fraction decrease with increasing heating rate except for the BMG (x = 1.32 at.%). The fragility indexes are 32–48 for the studied Zr-based BMGs. The present results are of guiding significance for preparing the excellent BMG composites by heat treatment and selecting suitable conditions for forming the BMGs.

The thermal, mechanical and corrosive properties of (Cu45Zr45.5Ti9.5)100-xAlx (x = 0–0.25 at%) glass forming alloys were systematically studied. The thermal measurements show that Al microalloying leads to increase of glass transition temperature but decrease of supercooled liquid region. The glass transition activation energy slightly increases and then decreases with increasing Al content. The room-temperature compression tests demonstrate that all studied Cu-based bulk metallic glasses (BMGs) exhibit work-hardening behavior, but the work-hardening capacity depends on Al content. In addition, yield strength, fracture strength and fracture strain are drastically increased by Al addition. The largest plasticity of (Cu45Zr45.5Ti9.5)99.8Al0.2 BMG is 6 times larger than that of the Al-free Cu-based BMG. Moreover, the electrochemical measurements indicate that the Al minor addition cause the decrease of both corrosion potential and corrosion current density. The corrosion behavior gradually transforms from the pitting corrosion to the self-passivization with increasing Al content. The local heterogeneity of Al element is thought to be the reason for the performance change of the studied Cu-based BMGs. The present results would provide a new insight into the mechanism for the microalloying effect on the properties of the metallic glasses.

This study explores nanosecond-pulsed (ns-pulsed) laser welding on the metallic glass (MG) ribbons of four compositions: Fe78Si9B13, Zr65Cu15Ni10Al10, La55Ni20Al25 and Ce65Al10Cu20Co5. All MGs can be welded in the air by the ns-pulsed laser, and the crystallization of the welding joints can be avoided by proper control of the laser parameters. By varying the travel speed, pulse duration and repetition frequency, the critical crystallization time of MG can be quickly detected in a high-throughput way by ns-pulsed laser welding. At the optimal processing conditions, 70–90% of the tensile strength of the parent melt-spun ribbon can be preserved in the welded MG ribbons. The mechanical strength is well linked to the profile of the welding joint, which suggests a simple method to evaluate the welding quality. A welding parameter map has been established based on the experiments, and it is concluded that the laser power-density per sample thickness and the interaction time are the key factors that control the crystallization and strength of the welding joints. The map is valid for a broad range of MG compositions of all sample thickness, and thus the optimal processing conditions may be extended to all MGs with equivalent glass-forming ability.

A group of plastic Zr-Al-Ni-Cu bulk metallic glasses (BMGs) with low Zr content was developed and their thermal and mechanical properties were investigated. The results show that these Zr-based BMGs have a single crystallization event for all heating rates in the studied temperature region. The glass transition temperature Tg decreases with increasing Zr content for all heating rates. There are two melting procedures for the BMGs whose Zr content is less than 52 at %, while three melting procedures for the other Zr-based BMGs. The second melting procedure is split into two melting procedures for Zr52.5Al12.2Ni12.6Cu22.7 and Zr53Al11.6Ni11.7Cu23.7 BMGs, while the first melting procedure is split into two melting procedures for the other BMGs. The activation energy decreases with increasing sensitivity index β for the studied Zr-based BMGs. The plastic strain ep is in the region of 0.2%-19.1% for these Zr-based BMGs. Both yield strength σy and fracture strength σf are smallest for Zr55Al8.9Ni7.3Cu28.8 BMG whose ep is largest among all studied Zr-based BMGs and reaches up to 19.1%. In addition, the mechanism for the large difference of the plasticity among the studied Zr-based BMGs is also discussed.

The effects of stress relief on the magnetic characteristics of Fe-based metallic glass (MG) ribbons are investigated under external stress through various annealing treatments. We found that long-time annealing treatments benefit for making softer magnetic MGs under applied bending stress. We show that the irreversible domain wall movement region and the irreversible domain wall rotation region in the M-H curve represent the stress relief, which can be well reflected by the demagnified magnetic anisotropy. The magnetic coercivity and effective permeability variations in the lower frequency regime also represent the stress relief state. These observations have implications for understanding the relationship between the stress relief, microstructure change, and magnetic softness in magnetic MGs and might be helpful for the performance improvement of the ferromagnetic glassy materials.

Fe-based metallic glasses (MGs) with excellent soft magnetic properties are applicable in a wide range of electronic industry. We show that the cryogenic thermal cycle has a sensitive effect on soft magnetic properties of Fe78Si9B13 glassy ribbon. The values of magnetic induction (or magnetic flux density) B and coercivity H c show fluctuation with increasing number of thermal cycles. This phenomenon is explained as thermal-cycle-induced stochastically structural aging or rejuvenation which randomly fluctuates magnetic anisotropy and, consequently, the magnetic induction and coercivity. Overall, increasing the number of thermal cycles improves the soft magnetic properties of the ribbon. The results could help understand the relationship between relaxation and magnetic property, and the thermal cycle could provide an effective approach to improving performances of metallic glasses in industry.