The effect of electromagnetic bulging on the fatigue behavior of the 5052 aluminum alloy was investigated through tensile–tensile fatigue testing. The intriguing finding is that the bulged specimens exhibited enhanced fatigue strength as depicted by maximum stress vs the number of cycles until failure (S–N) curves, by comparison with these original aluminum alloys. Although the fatigue process of the original and budged alloys follows the same mechanism with three distinct steps, namely, crack initiation at a corner of the tested samples, stable crack propagation with typical fatigue striations and finally catastrophic fracture with dimple fractographic features. The typical crack propagation rate vs stress intensity factor range (da/dN–ΔK) curves derived from the spacing of striations reveal a lower crack propagation rate in the bulged specimens. The enhancement of fatigue strength in electromagnetically bulged aluminum alloy is further rationalized in-depth on the basis of strain hardening and dislocation shielding effect.

•Colored Zr-based TFMGs were created by magnetic sputtering under Ar/N2 mixing atmosphere.•Colors of the TFMGs could be varied by changing the nitrogen content and film thickness.•Nitrogen doping led to the increase of hardness of the Zr-based TFMGs.•The mechanism of color changes in the Zr-based TFMGs was revealed.In this work, a novel approach for the preparation of a variety of colored thin film metallic glasses (TFMGs) is proposed. Based on magnetron sputtering technique using a mixture of nitrogen and argon as the sputtering gas, ZrCuFeAlAg TFMGs with a high hardness of 8.9 GPa and a variety of colors ranging from yellow to aqua to pink to purple were achieved by adjusting the nitrogen-doping content and the thickness of the thin films. It was revealed that the change of colors of the TFMGs is governed by a two-step mechanism: i) the TFMGs first became partially transparent by nitrogen doping owing to the formation of amorphous ZrxNy nitrides, which led to expansion of the energy band gap of the films, and ii) the color was varied by changing the thickness of the film due to the interference effect. The present work presents the possibility of making functional TFMGs for optical and electrical device applications.Download high-res image (224KB)Download full-size image

•A crack-free Zr-based bulk metallic glass composite was successfully fabricated by selected laser melting.•The composite exhibited high strength of about 1500 MPa.•Both low thermal stress and high fractural toughness responsible for the crack-free BMG composite in selected laser melting.3D printing of crack-free bulk metallic glasses remains challenge due to the generation of huge thermal stress during the selective laser melting and their intrinsic brittleness. Herein, Zr55Cu30Ni5Al10 system was selected and 3D printed by selective laser melting technique. The results indicated that bulk metallic glassy composite comprises a large fraction (about 83%) of amorphous phase and minor fraction of intermetallic compounds with free of cracks were successfully fabricated. The 3D printed metallic glassy composite exhibited high strength over 1500 MPa. Experiment combined with finite-element-method simulation not only revealed the mechanism of crystallization at heat affected zones, but demonstrated that low thermal stress reduce the risk of micro-cracks generation and fracture toughness plays a crucial role in suppression the crack propagation during selective laser melting process.

•The dealloying processes of Pd32Ni48P20 (at.%) amorphous alloy in H2SO4 solution were revealed.•Pd-based amorphous nanoporous structure has been synthesized by dealloying technique.•The amorphous nanoporous structure exhibits a superior catalytic activity toward methanol electro-oxidation.•The enhanced mechanism for this amorphous nanostructure was clarified.Pd-based catalysts are of interest for their application in direct alcohol fuel cells. This is due to the excellent electro-catalytic performance and relatively low cost. In this work, by electrochemical dealloying of Pd32Ni48P20 metallic glass at a relatively low potential (0.85 V) in sulfuric acid solution, a novel Pd-based nanoporous structure, composed of amorphous nanoparticles and interconnected conduits has been successfully fabricated. By contrast, Pd-based nanoporous network structure, consisting of crystalline ligaments and porous channels, was also fabricated by dealloying at a high potential (0.88 V). The former exhibited an enhanced catalytic activity (up to 160% increase) over the latter toward methanol electro-oxidation in alkaline medium, benefiting with the combination of amorphism and nanoporosity of the dealloyed nano-products. The excellent electro-catalysis provides promising perspective of the Pd-based amorphous nanoporous structure for the application in direct alcohol fuel cells.

•20% Al2O3 particle addition remarkably improves the impact resistance of amorphous coating.•Al2O3 particles absorb impact energy by crack deflection and micro-crack mechanisms.•Al2O3 particles alleviate the stress concentration upon impacting revealed by FEM.•The composite coating is more corrosion resistant than the monolithic coating after impact.The load-bearing applications of Fe based amorphous coatings are limited due to their poor impact resistance. Here, we have designed an amorphous composite coating reinforced with 20 wt% Al2O3 particles that is tougher and more impact resistant than the monolithic amorphous coating. Impact resistance of the coatings was systematically studied by drop-weight impact tests and finite element modelling (FEM). It was found that the hard Al2O3 particles in the composite coatings could effectively hinder crack propagation via the formation of micro-cracks inside the Al2O3 particles, which absorbs the impact energy. FEM indicates that the Al2O3 dispersion acts as the main loading-bearing phase and alleviates the stress concentration in the composite coating, thus suppresses crack initiation and propagation. Furthermore, electrochemical polarization test shows that composite coating remains good corrosion resistance in a 3.5% NaCl solution after impact.

Although corrosion and friction/wear behavior of Fe-based amorphous coatings and their composites has been extensively studied during the past decade, there is very limited work related to tribocorrosion behavior. In this paper, the tribocorrosion behavior of a Fe-based amorphous composite coating reinforced with 20 wt.% Al2O3 particles was investigated in a 3.5% NaCl solution on a ball-on-disk tester and was compared to the monolithic amorphous coating and 316L stainless steel (SS). The results showed that the amorphous composite coating exhibited the highest tribocorrosion resistance among the three materials tested, as evidenced by the lowest coefficient of friction (~0.3) and tribocorrosion wear rate (~1.2 × 10−5 mm3/N·m). In addition, potentiodynamic polarization measurements before and during tribocorrosion testing demonstrated that corrosion resistance of the amorphous composite coating was not influenced so much by mechanical loading compared to the amorphous coating and the 316L SS. Observations on the worn surface revealed a corrosion-wear- and oxidational-wear-dominated tribocorrosion mechanism for the composite coatings. The excellent tribocorrosion resistance of the composite coating results from the effect of chemically stable Al2O3 phase which resists oxidation and delamination during sliding, along with poor wettability with corrosive NaCl droplets.

Fatigue behaviors of a biocompatible Ni-free Zr60.14Cu22.31Fe4.85Al9.7Ag3 Zr-based bulk metallic glass (BMG) have been studied under three-point-bending test in a simulated body fluid (SBF) at 37 °C and compared with those in air at room temperature (RT). The BMG shows a high fatigue limit of approximately 366 MPa in SBF, which was slightly lower than that in air (400 MPa). The fatigue cracks tended to initiate from the defects such as cast-pores, inclusions and corners of the samples and propagate in a similar path in SBF and in air. Three distinct regions, i.e. a crack-initiation region, a stable crack-growth region and an unstable fast-fracture region were clearly observed on the fatigue-fractured surface. Although pitting occurred at the defects where crack initiated, it does not affect significantly the fatigue life of the BMG, because the lifetime in the present BMG is mainly determined by crack propagation. The high corrosion-fatigue limit of the studied BMG results from its excellent corrosion resistance in SBF and intrinsically good toughness.

•The amorphous coatings show excellent corrosion resistance and unusual pitting mechanisms in NaCl solution.•The amorphous coatings exhibit an oxidative and delamination wear mechanism.•The bonding strength of the coatings was 25–45 MPa in this work.•Highly hydrophobic coating can be directly fabricated via the surface roughness control.•The amorphous coating has potential applications in the military and industry.Bulk metallic glasses (BMGs), also called amorphous alloys, have totally different structure from the conventional crystalline metals and are well-known for their high strength and high hardness, large elastic limits, and, in particular, for their outstanding corrosion and wear resistance. During the past several decades, despite the understanding gained on the formation and microstructure, as well as the mechanisms related to their unique mechanical properties that have achieved great progress, industrial applications of BMGs are still very scant due to mostly the poor ductility at room temperature. In contrast, amorphous coatings based on BMG systems have received increasing attention and interest in recent years because of the combination of the excellent properties inherited from the bulk glassy alloys and the potential engineering applications for amorphous coatings. In this article, we briefly summarize the past development and the recent progress of amorphous coatings made in our group in terms of fabrication, microstructure, thermal stability, and properties such as corrosion and wear resistance, bonding strength and wettability. In addition, we also describe simply the foreseen potential applications and future developments of this kind of materials.

•Nanoporous Cu with various pore sizes were fabricated by dealloying MgCuGd metallic glasses.•Samples with larger pore size exhibit higher catalytic activity in degrading phenol.•Pore size and wettability play a key role in achieving high catalytic performance.•The degradation mechanism of phenol by nanoporous samples is discussed.Nanoporous Cu with tunable pore size (20–50 nm) are synthesized through chemical dealloying of the Mg65Cu25Gd10 metallic glass in sulfuric acid solution. X-ray diffraction (XRD) and scanning electron microscopy (SEM) demonstrated the formation of mixing structures consisting of amorphous matrix and fcc-Cu ligaments with nanoporous structure in the dealloyed samples. The nanoporous alloy obtained shows superior catalytic activity in degrading phenol-containing wastewater, e.g., the degradation rate increases by 2–4 times as compared to the un-dealloyed Mg-based metallic glass. It was also found that surface wettability plays an important role in degradation, which results in a better catalytic performance in the sample with coarser nanoporous structure although it has relatively less specific surface area as compared to the samples with finer pores. Finally, the mechanism for degradation of phenol is discussed.

In this paper, pure Cu sheet with thickness of 1 mm was electromagnetically budged to form a conical shape workpiece. The deformation behavior and the microstructural evolution of the Cu sheet under electromagnetic bulging were systematically studied using strain analysis, optical microscopy (OM), electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). It is found that the strain distribution in the workpiece is quite un-uniform from the bottom to the top due to the inhomogeneous electromagnetic pressure generated by the spiral coil. The characterization of microstructure reveals that the bulge deformation of the Cu sheet is governed by dislocation multiple slip and cross slip, which cause finally the formation of cell structures. However, the size and the boundary width of cells are closely related to the plastic strain, i.e., the cell size and boundary width decrease with increasing strain. In addition, low misorientation angle of cells inside the grains increases with increasing strain. This structural evolution is discussed on the basis of the low energy dislocation structures (LEDS) theory.

Bonding strength is one of the most important properties in thermally sprayed coatings as it plays crucial roles in the performance and lifetime of the coatings. This study aims to explore different factors that affect the bonding strength of the Fe48Mo14Cr15Y2C15B6 amorphous coating prepared by high velocity oxygen fuel (HVOF) thermal spraying. The results demonstrate that the substrate roughness and the coating thickness have significant influence on the bonding strength of the amorphous coating, e.g. the bonding strength increases when the substrate roughness is above a certain threshold, and decreases with the increasing coating thickness. In addition, the bond strength can be effectively enhanced via the addition of an intermediate NiCrAl layer between the substrate and the amorphous coating due to the occurrence of metallurgical reaction and the improved interfacial structure. Finally, the fracture mechanism of the coatings was also discussed.Highlights► Bonding strength of amorphous coating increased with an increasing substrate roughness. ► Bonding strength of the coating decreased with the increasing coating thickness. ► Bonding strength was significantly enhanced via an intermediate NiCrAl coating. ► Crack mostly initiated at the boundaries of un-melted particles in the coating

The deformation behavior of the Zr69.5Cu12Ni11Al7.5 bulk metallic glass (BMG) was examined by compression, tension and three-point bending test. It was found that the BMG exhibits excellent room temperature plasticity and toughness with a compressive strain over 11.5%, a tension strain of about 0.2–0.3% and a notch toughness of 86 ± 5.5 MPa m1/2. Structural analyses revealed that the existence of strong icosahedral medium-range order (IMRO) clusters in amorphous phase, which contributes to the good plasticity and toughness of the BMG studied.Highlights► Zr69.5Cu12Ni11Al7.5 metallic glass exhibits excellent plasticity and toughness. ► The compressive strain is over 11.5% and tension strain of about 0.2–0.3%. ► The notch toughness is 86 ± 5.5 MPa m1/2. ► There is a strong icosahedral medium-range order clusters in amorphous phase. ► There is no crystallization in shear band during plastic deformation.

The wear behavior of Fe48Cr15Mo14C15B6Y2 amorphous coatings prepared by high velocity oxygen fuel (HVOF) thermal spraying was studied under dry sliding conditions in a ball-on-plate mode using alumina ball as the counterpart. It was found that the friction coefficient and the wear rate of the coating are around 0.3–0.4, and (3–19) × 10−5 mm3 N−1 m−1, respectively. Compared with traditional steels and other wear-resistant coatings, such as hard Cr and Al2O3 coatings, the Fe-based amorphous coating shows higher wear resistance. The wear rate is independent of the applied load, but increases linearly with the increase of sliding speed. The dominating wear mechanism of the Fe-based amorphous coating is by oxidative wear coupled with delamination wear, where the oxidation process is governed by inward diffusion of oxygen.Highlights► The high velocity oxygen fuel sprayed Fe-based amorphous coatings show excellent wear resistance. ► It is about 2–3 times better than the AISI 1045 steel substrate and conventional hard Cr coating. ► The wear rate of the amorphous coatings increase linearly with increasing sliding speed. ► The wear mechanism of the Fe-based amorphous coating is dominated by oxidative wear coupled with delamination wear. ► Oxidation process is governed by inward diffusion of oxygen.

The Fe-based amorphous coatings with the composition of Fe48Cr15Mo14C15B6Y2 were successfully sprayed on mild steel substrate by the high velocity oxygen fuel (HVOF) spraying process with different feedstock powder sizes (i.e., powder A: −33 + 20 μm, powder B: −45 + 33 μm, powder C: −55 + 45 μm). The coatings were characterized for its morphology, microstructure and thermal stability by using X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The corrosion behavior of the coatings in 3.5 wt% NaCl solution was studied with potentiodynamic and potentiostatic polarization test. It was found that the particle size of the feedstock powders had a significant influence on microstructure and corrosion resistance of the resultant coatings. The coatings sprayed with the finest powders show the most compact structure; while the coating with the coarser powders exhibits a better corrosion resistance. It is found that the corrosion resistance of the coatings is closely related to the wetting behavior which is affected by the oxygen content and the roughness of coatings. The coatings with hydrophobicity exhibit a better corrosion. The present result demonstrates that the amorphous coatings with hydrophobicity and excellent corrosion resistant are promising for industrial application in marine environment.Highlights► Fe-based amorphous coatings from different particle sizes of powders were prepared. ► Increasing the particle size will decrease the oxygen content but increase porosity in coating. ► Increasing the particle size will enhance the hydrophobic property of coatings. ► The more hydrophobic is, the better corrosion resistance will be. ► The wettability of coating is closely related with its porosity and oxygen content.

The notch fracture toughness of Fe75Mo5P10C8.3B1.7 monolithic bulk metallic glass (BMG) and Fe77Mo5P9C7.5B1.5 and Fe79Mo5P8C6.7B1.3 BMG matrix composites with α-Fe as reinforcing phase, fabricated by suction mould casting, were evaluated. It was found that the monolithic BMG has a toughness of 27 MPa m1/2, while the Fe77Mo5P9C7.5B1.5 BMG composite reinforced by single α-Fe dendrite phase exhibits a higher toughness of nearly 40 MPa m1/2. However, for the Fe79Mo5P8C6.7B1.3 alloy with more dendrites, the toughness decreased up to 25 MPa m1/2. Microstructure investigation reveals that the simultaneous formation of Fe–Mo–P hard brittle phase apart from α-Fe dendrites in the Fe79Mo5P8C6.7B1.3 alloy is the reason for the degradation of the fracture toughness.Highlights► We examine the notch fracture toughness of the three Fe-based alloys including one monolithic BMG, and two BMG matrix composites. ► The toughness could be significantly enhanced by formed single α-Fe dendrite. ► The intrinsic properties of precipitation phase play more important role in the fracture toughness rather than the formation of dendrite phase.

The plastic deformation of Zr65Cu17.5Ni10Al7.5 bulk metallic glass with different diameters (Ø 1–4 mm) but the same initial atomic-scale structure was investigated through compression at room temperature. It was found that the plastic strain increases with decreasing sample dimension, and this tendency becomes more prominent when the diameter of the specimen decreases to 1 mm, indicating a size dependent plasticity. Correspondingly, the morphology of sheared surface also shows size dependence. The fracture surface is characterized by typical vein-like patterns for the sample with large diameter, but for the small size sample, the sheared surface exhibits regular spaced striations. The origin of shear-banding instability that is responsible for the size dependent plasticity is discussed in terms of the adiabatic heating and the free volume model.

A bone-like apatite layer was successfully deposited on the surface of the Ni-free Zr60.5Cu19.5Fe5Al9.5Ti5.5 bulk metallic glass (BMG) by using a hybrid technique of micro-arc oxidation (MAO) and a biomimetic process. The Zr-based BMG was initially modified via MAO which led to the formation of a porous and rough ZrO2 layer on the BMG surface. After subsequent immersion in a simulated body fluid, a bone-like apatite could be spontaneously and promptly formed on the ZrO2 layer, demonstrating a good bioactivity. The present work provides a promising technique for bioactive surface modification of Zr-based bulk metallic glasses, which could pave a way to medical application of the newly developed BMG materials.

The tensile deformation behavior of Zr55.9Cu18.6Ni10Al7.5Ta8 bulk metallic glass composite was investigated in the supercooled liquid region at various strain rates and temperatures. The deformation of the bulk metallic glass composite exhibited superplastic behavior, which is closely related to the strain rate and temperature. This excellent superplasticity, with a maximum elongation over 650%, indicates that the bulk metallic glass composite looks promising for thermoplastic forming applications.

A significant enhancement of the room-temperature plasticity was realized by the micro-addition of 1 at% Fe in a CuZrAl bulk metallic glass (BMG). It was found that the phase separation by the formation of a Cu-rich phase and a Fe-rich phase is responsible for the improvement of plasticity of the CuZrAl BMG. The result provides a promising approach to enhance the plasticity of BMGs through compositional and structural design by microalloying.

The effect of Ag addition on the glass forming ability (GFA) and mechanical properties of (Zr0.62Cu0.23Fe0.05Al0.10)100−xAgx (x = 0, 1, 3, 5, 7) alloys were investigated by X-ray diffractometry, differential scanning calorimetry and compression testing. Their GFA and plasticity are found to increase simultaneously with increasing Ag content up to 3 at.%, but beyond this range, they both decrease. The (Zr0.62Cu0.23Fe0.05Al0.10)97Ag3 alloy exhibits the highest GFA and largest plasticity, with a critical diameter of 10 mm and a fracture plastic strain of 5.2%. The reasons for the enhanced GFA and plasticity are discussed by considering the positive heat of mixing between Ag, Cu and Fe. The Ni-free (Zr0.62Cu0.23Fe0.05Al0.10)97Ag3 alloy with high GFA, reasonably good plasticity and a low Young's modulus of approximate 68 GPa is a promising candidate for biomedical applications.

Three Ni-free Zr-based BMGs with composition of Zr60Nb5Cu20Fe5Al10, Zr60Nb5Cu22.5Pd5Al7.5, Zr60Ti6Cu19Fe5Al10 were fabricated by suck copper-mould casting. All the BMGs prepared exhibit good glassy forming ability and wide supercooled liquid region ranging from 38 to 99 K. These BMGs also show good mechanical properties under static compression with yield strength of over 1350 MPa, Young's modulus of 70–80 GPa, and plastic strain of 3.6–9.5%. Friction and wear tests revealed that the BMGs exhibit much better wear resistance than the medical alloy Ti6Al4V, although BMGs have a higher friction coefficient. In addition, the in vitro test indicated that the BMGs have a similar or even better cell viability and proliferation activity as compared with Ti6Al4V. Finally, the in vivo evaluation of the BMGs was carried out by the implantation of BMG samples into white rabbits. It is shown that the BMG implants performed as well as the Ti alloy, demonstrating that the Ni-free Zr-based BMGs developed in this work are promising in medical applications.

Instrumented nanoindentation was conducted on an Au49Ag5.5Pd2.3Cu26.9Si16.3 bulk metallic glass from room temperature to supercooled liquid region. It was found that the hardness decreases as the depth of the indentation increases at a modest loading rate (e.g. ∼0.5 mN s−1), which is known as the indentation size effect (ISE). The transition from inhomogeneous to homogeneous flow was clearly observed at the glass transition temperature. However, the deformation behavior of the metallic glass in the supercooled liquid region showed strong loading rate dependence. The deformation mode changed from homogeneous to inhomogeneous, and even exhibited a reverse indentation size effect when the loading rate was sufficiently high (i.e., ≥10 mN s−1 in the study). The different deformation behaviors and indentation size effects at various temperatures and loading rates are discussed in terms of free volume theory.

A significant enhancement of the room-temperature plasticity was realized by the micro-addition of 1 at% Fe in a CuZrAl bulk metallic glass (BMG). It was found that the phase separation by the formation of a Cu-rich phase and a Fe-rich phase is responsible for the improvement of plasticity of the CuZrAl BMG. The result provides a promising approach to enhance the plasticity of BMGs through compositional and structural design by microalloying.