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Abstract Capturing a shear band in a metallic glass during its propagation experimentally is very challenging. Shear bands are very narrow but extend rapidly over macroscopic distances, therefore, characterization of large areas at high magnification and high speed is required. Here we show how to control the shear bands in a pre-structured thin film metallic glass in order to directly measure local strains during initiation, propagation, or arrest events. Based on the experimental observations, a model describing the shear banding phenomenon purely within the frameworks of continuum mechanics is formulated. We claim that metallic glasses exhibit an elastic limit of about 5% which must be exceeded locally either at a stress concentrator to initiate a shear banding event, or at the tip of a shear band during its propagation. The model can successfully connect micro- and macroscopic plasticity of metallic glasses and suggests an alternative interpretation of controversial experimental observations.

As highly integrated circuits continue to advance, accompanied by a growing demand for energy efficiency and weight reduction, materials are confronted with mounting challenges pertaining to thermal conductivity and lightweight properties. By virtue of numerous intrinsic mechanisms, as a result, the thermal conductivity and mechanical properties of the Mg alloys are often inversely related, which becomes a bottleneck limiting the application of Mg alloys. Based on several effective modification methods to improve the thermal conductivity of Mg alloys, this paper describes the law of how they affect the mechanical properties, and clearly indicates that peak aging treatment is one of the best ways to simultaneously enhance an alloy's thermal conductivity and mechanical properties. As the most frequently used Mg alloy, cast alloys exhibit substantial potential for achieving high thermal conductivity. Moreover, recent reports indicate that hot deformation can significantly improve the mechanical properties while maintaining, and potentially slightly enhancing, the alloy's thermal conductivity. This presents a meaningful way to develop Mg alloys for applications in the field of small-volume heat dissipation components that require high strength. This comprehensive review begins by outlining standard testing and prediction methods, followed by the theoretical models used to predict thermal conductivity, and then explores the primary influencing factors affecting thermal conductivity. The review summarizes the current development status of Mg alloys, focusing on the quest for alloys that offer both high thermal conductivity and high strength. It concludes by providing insights into forthcoming prospects and challenges within this field.

In this work, an in-situ boride-reinforced Ti6Al4V compositionally graded material was prepared successfully by spark plasma sintering (SPS), and exhibited a good potential for military application because of its stepwise transition properties from a high-toughness end to a high-strength end along the thin-thickness direction. Microstructure characterization shows the chemical gradient ranged from 0 to 30 wt% TiB2 along the thickness direction, which was correlated with increasing micro-hardness values ranging from 565±5HV to 1270±5HV, respectively. The strength-toughness matching mechanisms of the gradient composites with different compositional gradients were discussed based on the static compression experiments and the dynamic Hopkinson compression rod experiments. The primary phases of the gradient composites included the α-Ti phase, β-Ti phase, remained TiB2 and in-situ formed whisker-like TiB phases. The composites with a compositional gradient of G84 (0, 0, 15, 30 wt%) exhibited the best impact resistance which achieved a good balance of high toughness and strength, and exhibited a compressive strength of 2148±5 MPa and a good elongation of 20 ± 0.5%. The strength-toughness matching mechanisms can be explained by the dispersion strengthening effect due to the presence of the in-situ formed TiB phase, and the consumption of more fracture energy by dislocation defects, which can prevent the crack propagation. Moreover, the pull-out of the whisker-like TiB phases toughened the gradient composites furthermore. This research demonstrated a reliable method for preparing TiB2/Ti–6Al-4Vgradient composites with high-impact resistance.

Abstract Residual stress engineering is widely used in the design of new advanced lightweight materials. For metallic glasses, attention has been given to structural changes and rejuvenation processes. High-energy scanning X-ray diffraction strain mapping reveals large elastic fluctuations in notched metallic glasses after deformation under triaxial compression. Microindentation hardness mapping hints at a competing hardening–softening mechanism after compression and reveals the complementary effects of stress and structure modulation. Transmission electron microscopy proves that structure modulation and elastic heterogeneity distribution under room temperature deformation are related to shear band formation. Molecular dynamics simulations provide an atomistic understanding of the confined deformation mechanism in notched metallic glasses and the related fluctuations in the elastic and plastic strains. Thus, future focus should be given to stress modulation and elastic heterogeneity, which, together with structure modulation, may allow the design of metallic glasses with enhanced ductility and strain-hardening ability.

Ni60/60% WC composite coatings with a good surface roughness and high mechanical properties were successfully prepared on 316L stainless steel substrate by laser-directed energy deposition (LDED) technology. The effects of laser power on the microstructural evolution and mechanical properties of the Ni60/60% WC composite coating were investigated. The relationships between the chemical composition, the microstructure, the hardness, and the friction wear resistance of the composite coatings were characterized and investigated. The results show that the laser power had a significant effect on the energy input, which determined the melting extent of the Ni60 phases around the WC particles and the bonding strength between the reinforcements and the matrix, as well as the bonding strength between the substrate and the coatings. With an increase in the laser power from 800 W to 1400 W, the average hardness of the coating surface increased due to the increased densification of the deposited coatings and then decreased due to grain coarsening under a high energy input. The average coefficient of friction of the coatings decreased gradually to 0.383 at 1000 W, showing a minimum wear of 0.00013 mm2 at 1200 W. The main wear mechanisms on the coated surfaces were adhesive wear and abrasive wear. Moreover, the coatings deposited at 1200 W exhibited better forming quality and wear resistance. This work suggests that the processing parameters during LDED can be optimized to prepare Ni60/60% WC wear-resistant coatings with excellent mechanical properties.

During the laser-based directed energy deposition (DED-LB) processing, a WC-12Co composite coating with high hardness and strong wear resistance was successfully prepared on a 316L stainless steel substrate by adopting a high-precision coaxial powder feeding system using a spherical WC-12Co composite powder, which showed a large number of dendritic carbides and herringbone planar crystals on the substrate-binding interface. The influences of laser power on microstructural and mechanical properties (e.g., hardness, friction resistance) of WC-12Co composite surfaces were investigated. The results show that laser power has a significant effect on determining the degree of Co phase melting around the WC particles and the adhesion strength between the matrix and the coating. Lower laser power does not meet the melting requirements of WC particles, thus weakening the molding quality of the composite coating. At high laser power, it is possible to dissolve the WC particles and melt the metal powder between the particles, thus improving the material properties. The laser power increased from 700 W to 1000 W and the average hardness of the coating surface gradually increased from 1166.33 HV to 1395.70 HV, which is about 4–5 times higher than the average hardness of the substrate (about 281.76 HV). In addition, the coatings deposited at 1000 W showed better wear resistance. This work shows that the processing parameters during laser-directed energy deposition can be optimized to prepare WC-12Co composite coatings with excellent mechanical properties.

High-entropy alloys (HEAs) have attracted considerable attention for their exceptional microstructures and properties. Discovering new HEAs with desirable properties is crucial, but traditional design methods are laborious and time-consuming. Fortunately, the emerging Machine Learning (ML) offers an efficient solution. In this study, composition-microhardness data pairs from various alloy systems were collected and expanded using a Generative Adversarial Network (GAN). These data pairs were converted into empirical parameter-microhardness pairs. Then Active Learning (AL) was employed to screen the Al-Co-Cr-Cu-Fe-Ni system and identify the eXtreme Gradient Boosting (XGBoost) as the optimal ML master model. Millions of data training iterations employing the XGBoost sub-model and accuracy evaluations using the Expected Improvement (EI) algorithm establish the relationship between HEA compositions and microhardness. The proposed sub-model aligns well with experimental data, wherein four Al-rich compositions exhibit ultra-high microhardness (>740 HV, with a maximum of ∼780.3 HV) and low density (

Hydrogen is considered one of the most ideal future energy carriers. The safe storage and convenient transportation of hydrogen are key factors for the utilization of hydrogen energy. In the current investigation, two-dimensional vanadium carbide (VC) was prepared by an etching method using V4AlC3 as a precursor and then employed to enhance the hydrogen storage properties of MgH2. The studied results indicate that VC-doped MgH2 can absorb hydrogen at room temperature and release hydrogen at 170 °C. Moreover, it absorbs 5.0 wt.% of H2 within 9.8 min at 100 °C and desorbs 5.0 wt.% of H2 within 3.2 min at 300 °C. The dehydrogenation apparent activation energy of VC-doped MgH2 is 89.3 ± 2.8 kJ/mol, which is far lower than that of additive-free MgH2 (138.5 ± 2.4 kJ/mol), respectively. Ab-initio simulations showed that VC can stretch Mg-H bonds and make the Mg-H bonds easier to break, which is responsible for the decrease of dehydrogenation temperature and conducive to accelerating the diffusion rate of hydrogen atoms, thus, the hydrogen storage properties of MgH2 are remarkable improved through addition of VC.

The laser drilling of carbon steel is always suffered from the formation of slag, the presence of cutting burrs, the generation of a significant quantity of spatter, and the incomplete penetration of the substrate. In order to avoid these defects formed during the laser drilling of carbon steel, the COMSOL multi-physics simulation method was used to model and optimize the laser drilling process. Considering the splash evolution of the material during the complex drilling process, the transient evolution of the temperature field, the flow of the molten fluid, the geometrical changes, and the absorption of the laser energy during the laser drilling process were investigated. The simulated borehole dimensions are consistent with the experimental results. The process parameters have a great influence on the fluid flow pattern and material slag splashing. The laser power has a significant effect on the laser processing compared with the process parameters. With the increase in laser power and the decrease in laser heat source radius, the time required for perforation is reduced, the flow of melt is accelerated, the perforation efficiency is increased, and the hole wall is smoother, but the degree of spattering is greater. The optimized process parameters were obtained: laser heat source radius of 0.3 mm, laser power of 3000 W. These findings can help reduce the machining defects in carbon steel with excellent mechanical properties by optimizing the laser drilling processing parameters.

Abstract To alleviate the mechanical instability of major shear bands in metallic glasses at room temperature, topologically heterogeneous structures were introduced to encourage the multiplication of mild shear bands. Different from the former attention on topological structures, here we present a compositional design approach to build nanoscale chemical heterogeneity to enhance homogeneous plastic flow upon both compression and tension. The idea is realized in a Ti-Zr-Nb-Si-XX/Mg-Zn-Ca-YY hierarchically nanodomained amorphous alloy, where XX and YY denote other elements. The alloy shows ~2% elastic strain and undergoes highly homogeneous plastic flow of ~40% strain (with strain hardening) in compression, surpassing those of mono- and hetero-structured metallic glasses. Furthermore, dynamic atomic intermixing occurs between the nanodomains during plastic flow, preventing possible interface failure. Our design of chemically distinct nanodomains and the dynamic atomic intermixing at the interface opens up an avenue for the development of amorphous materials with ultrahigh strength and large plasticity.

The thermo-mechanical and failure behavior of the burning-free Al2O3 –C–SiO2 slide gate plate materials during the steel casting process are investigated. Firstly, the instantaneous coefficient of thermal expansion and the Young's modulus of the slide gate plate materials with different component contents at high temperature are measured. Secondly, a material constitutive model and a concrete damage plasticity mode are established based on the experiments, and adopted to simulate the failure behavior of the burning-free Al2O3–C–SiO2 slide gate plate during casting based on Finite Element Method (FEM) analysis. Results show that temperature gradient in the slide gate plate near the casting hole increased significantly and had a significant influence on cracking. The area near the casting hole of the slide gate plate is under tensile stress conditions, and then changes towards compressive stress conditions. Under those severe thermal stress conditions, crack formation is evaluated and an optimized composite structure of the slide gate plate combining advantages of reducing the risk of cracking and extending the service life is proposed. Moreover, the thermal shock test further verified that the microcrack extension was significantly alleviated due to the SiC distributed in whisker form and formed an interlocking structure in material. This work provides a reliable theoretical and experimental basis for the design and optimization of high performance Al2O3–C–SiO2 slide gate plates.

Voids are probably the most widely studied type of manufacturing defects since they are often formed during material processing. In this paper, the fracture and plastic deformation of Cu/Cu64Zr36 crystalline/amorphous composites with different void locations and shapes are investigated by molecular dynamics simulations. The results show that changes of the void location and shape in the composites significantly change the dislocation motion, shear transformation zones (STZs) activation, shear band propagation, and fracture strength of the composites. The largest shear strain is always found around the void, where it is most likely to activate dislocation motion, STZs and shear band formation. A stepwise increase of the shear localization is mainly related to the nucleation and emission of dislocations, while the very rapid increase is caused by shear band formation. Moreover, the variation of dislocation density and activity of shear bands are mainly responsible for the stress fluctuations in the composites. This paper provides important information for understanding and improving the plastic and fracture behaviors of composites by changing the location and shape of void from an atomistic perspective.

Large eutectic carbides presenting in the matrix deteriorate the mechanical properties of high carbon martensitic stainless steel. In the present work, nitrogen-alloyed martensitic stainless steel with different C/N ratios were designed by partial substitution of C by N of 9Cr18Mo, and their microstructure and mechanical properties were investigated. The results show that, with increasing the content of N up to 0.15 wt% in the experimental steel, the quantity and the size of eutectic carbides decrease； and the net-work eutectic carbides are gradually eliminated. The microstructure of all the steels is composed of lath martensite, twin martensite and M23C6 carbides. With partial substitution of C by N, the morphology of martensite blocks evolves from a lath shape to a blocky one, the quantity of twin martensite increases, and the nano-scaled Cr2N nitrides precipitate in the martensite matrix. The steel containing 0.15 wt% N exhibits the hardness of 60.5 HRC, a fracture strength of 1900 MPa and an elongation rate of 1.6 % due to hot rolling and heat treatment, which is attributed to the refinement of carbides and grains, solid solution of C and N, as well as the dense dislocation.

In order to develop materials for energy storage, a bulk nanocomposite with a composition of FeTi-25 vol% Cu was prepared by high-pressure torsion, with FeTi as functional phase for hydrogen storage and Cu as ductile phase to improve the processability. Despite the use of such a highly ductile auxiliary phase, the processability remained challenging due to strain localization in the softer Cu. This behavior is most pronounced at room temperature, and no nanocomposites were formed. At elevated temperatures, the strong strain rate sensitivity of the flow stress of the nanocrystalline Cu facilitates the formation of a FeTi–Cu nanocomposite due to a self-reinforcing process. Nevertheless, fragmentation of FeTi is limited because the resulting massive strain hardening prevents controlled processing at temperatures 250 °C. Satisfactory microstructural homogeneity is only achieved at the highest deformation temperatures of 550 °C. Overall, this study highlights that for unlikely material pairings, as often required in the pursuit of superior functional materials, the mechanical behavior of the phases involved and their interplay remains critical and must be thoroughly investigated when aiming for controlled structural homogeneity of bulk nanomaterials.

In this work, a new design principle, i.e. doping with refractory metal particles with a low diffusion rate to prevent the formation of cracks and to improve the mechanical properties of bulk metallic glass (BMG) composites, was put forward. It was proven that crack-free and dense Mo(p)/Cu47Zr47Al6 BMG composites with enhanced mechanical properties can be produced via LPBF. The dislocations generated in the Mo particles can release thermal stress, thereby inhibiting the formation of thermal-cracks. The fracture patterns of Mo particles show that they can delay rapid of crack expansion, thereby improving the inherent strength and toughness of the material.

The application of highly biocompatible advanced materials leads to fewer complications and more successful medical treatments. This study proposes Ti40Zr10Cu36Pd14 bulk metallic glass (BMG) as an oral implant material and provides insights into its possible processing routes, where high-temperature compression molding via an optimized process is adopted to both evaluate the thermoplastic net-shaping kinetics and tune the specific properties of the alloy. We present processed BMGs and BMG composites of the same composition with improved thermomechanical stability, from which high strength retention at temperatures, compared to the cast glass, by above 100 K higher is registered via dynamic mechanical analysis. ∼100 nm thin surface layers comprised of Ti, Cu, and Zr oxides form at the surface of the alloys, as identified by high-resolution transmission microscopy. Also, ∼4 orders of magnitude lower passivation current density along with ∼2 orders of magnitude lower corrosion current density of the processed glass compared to the values of the as-cast state confirms an extremely high stability in a 0.9 wt% saline environment which can be linked to surface hydrophobicity. Cytocompatibility analysis conducted by seeding human gingival fibroblast cells directly onto the thermoplastically formed Ti40Zr10Cu36Pd14 BMG reveals no adverse effect on cytocompatibility. On the other hand, the formation of a nanoscale oxide layer on the thermoplastically formed samples leads to significantly higher cell attachments on the surface.

To expand the basis for property-oriented material design, complex relationships between chemistry, atomistic structure, and properties of sputter-deposited AgxAu85-xSi15 alloys are investigated using versatile experimental methods. According to differential scanning calorimetry and X-ray diffraction data, the alloys are amorphous within a wide compositional range of 20 ≤ x ≤ 60 at%. However, high-resolution transmission electron microscopy revealed noticeable amounts of crystallites in limiting compositions with x = 20 at% and x = 60 at%. Glass transition and crystallization temperatures grow with increasing Ag content, while room-temperature resistivity and temperature coefficient of resistance are shown to be highly sensitive to the amount of crystalline phase. Neither the existence of nanocrystallites nor the substitution of Ag by Au affected significantly the mechanical properties. All compositions exhibit similar nanoindentation hardness of about 4.3 GPa, Young’s modulus of about 55 GPa, and macroscopic elastic limit of about 2%. The unique combination of high hardness, high elastic strain but low Young’s modulus together with the expected chemical inertness inherited from noble metals makes this alloy family suitable for biomedical applications in form of coatings or in jewelry if an economic bulk production route will be developed.

We introduce four new biocompatible toxic element-free Ti-based metallic glass (MG) compositions with constant metalloid (Si10B5) and varying precious metal (PM) contents for simultaneous improvement in glass-forming ability (GFA) and corrosion properties. Being completely free from cytotoxic elements like Cu, Ni, or Be, which are indispensable for Ti-based bulk metallic glass production, limits the GFA of the studied alloys significantly. However, avoiding these elements also realizes an unprecedented corrosion resistance in simulated body fluids, which supports the potential utilization of the alloys as long-lasting dental implant material. The novel Ti60Zr15Si10B5Pd10, Ti60Zr15Si10B5Pt10, Ti60Zr15Si10B5Pd5Pt5, Ti60Zr15Si10B5Pd5Au5 alloys are obtained in ribbon form using conventional single-roller melt spinning. The effect of the PM additions on the GFA and corrosion resistance of the alloys is investigated comparatively with each other by synchrotron X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, and cyclic polarization tests. Further, their Vickers hardness values are deduced using an ultra-sensitive micro indentation method, and the findings are discussed based on the composition dependence. It was found that the Ti60Zr15Si10B5Pd5Pt5 alloy presents a promising GFA while showing outstanding corrosion resistance in a simulated body fluid at 310 K.

Recent investigations have demonstrated that the plasticity of bulk metallic glasses (BMGs) at room temperature can be improved by artificially introducing both macroscopic and microscopic defects. In this work, both surface grooves and multiple shear bands (MLSBs) are concurrently introduced into the surface of a Zr65Cu15Ni10Al10 BMG employing an ultrasonic bonding machine, whose sizes are also tailored by tuning gas pressures and times. After surface treatment, MLSBs appear around grooves due to the pre-plastic deformation, while numerous nano-scale crystals resulting from thermal-induced nanocrystallization appear within the grooves, leading to the emergence of hierarchical structural heterogeneities. As a result, the strength and plasticity are effectively enhanced compared to as-cast samples when suitable experimental parameters are adopted. The plastic deformation mechanisms change from single main shear banding to multiple shear banding. Therefore, the serrated plastic behaviors exhibit a transition from chaotic to self-organized critical dynamics after surface treatment, confirming the modification of the shear banding instability. The present study provides a viable method to tailor the mechanical properties of BMGs and sheds light on their dynamic plastic deformation behaviors.

The addition of hybrid ceramic reinforcing phases provides the possibility of regulating the in-situ reaction and effective strengthening in laser additive manufactured aluminum matrix composites (AMCs). In this work, AMCs reinforced with (ZrC + TiC) solid solution ceramics with micro/nanoscale microstructural features are fabricated by laser powder bed fusion (LPBF). The influence of laser power on the manufacturing quality, the microhardness and the wear properties of the LPBF-fabricated (ZrC + TiC)/Al composites is investigated. Moreover, the reaction mechanism between the ZrC and TiC ceramics in the LPBF process is revealed. The tensile properties of the (ZrC + TiC)/Al composites with different (ZrC + TiC) contents prepared at optimal process parameters are compared. During the LPBF process, the ZrC and TiC ceramics are incompletely melted. On the ceramic particles, a thin (Ti,Zr)C layer formed and large amounts of (Ti,Zr)C nanoparticles precipitated via a dissolution-precipitation mechanism. When the laser power increases from 375 to 425 W, the manufacturing quality, microhardness, tensile and wear properties of the (ZrC + TiC)/Al composites increase. The tensile strength of 10 wt.% (ZrC + TiC)/Al composites prepared at optimal processing parameters reaches a high strength value of ∼227 MPa with a uniform elongation of ∼6.7%, which is three times higher than that of the unreinforced Al-matrix. This is ascribed to the combined effects of Orowan strengthening, coefficient of thermal expansion (CTE) mismatch strengthening, load-bearing strengthening and grain refinement strengthening.

Abstract Metallic glasses (MG) have attracted much attention due to their superior hardness and good corrosion resistance. However, designing new MG compositions is still a big challenge, and their integration into different systems is limited when they are in the shape of bulk materials. Here, we present a new method for the fabrication of MG in the form of microfibers which could greatly help them to be integrated within different systems. The newly proposed technique has the ability to form MG structure from commercially available alloy compositions thanks to its significantly improved quenching rate(~ 108 K.s−1). In this technique, individual melt droplets are ejected on a rotating wheel forming a thin film which are ruptured upon solidification leading to the formation of MG microfibers. In this regard, we have fabricated microfibers from a commercial DIN 1.4401 stainless-steel which could form a completely amorphous structure confirmed by DSC, XRD, and HRTEM. The fabricated MG microfibers show an increased hardness for more than two-fold from 3.5 ± 0.17 GPa for the as-received stainless-steel to 7.77 ± 0.60 GPa for the amorphous microfibers. Subsequent heat-treatment of the microfibers resulted in a nanocrystalline structure with the presence of amorphous regions when the hardness increases even further to 13.5 ± 2.0 GPa. We propose that confinement of both shear transformation zones and dislocations in the heat-treated MG microfibers plays a major role in enhancing strength.

Abstract Widespread application of magnesium (Mg) has been prevented by its low strength and poor corrosion resistance. Core of this limitation is Mg’s low electrochemical potential and low solubility for most elements, favoring secondary phase precipitation acting as effective micro-galvanic elements. Mg-based metal–metal composites, while benefiting strength, are similarly active galvanic couples. We show that related detrimental corrosion susceptibility is overcome by nanoscale composite architecture design. Nanoscale phase spacings enable high-strength Mg–Fe composites with degradation rates as low as ultra-high purity Mg. Our concept thus fundamentally changes today’s understanding of Mg’s corrosion and significantly widens the property space of Mg-based materials.

Pure metals tend to have a superior malleability compared to alloys. However, the applicability of pure metals is limited by their low strengths and hardness properties. In this study, strong and ductile pure Ti was synthesized via an approach involving powder modification and additive manufacturing (AM) under a reactive atmosphere. Specifically, pure Ti was processed by laser powder bed fusion in an environment containing a mixture of argon and nitrogen gases. In-situ high-energy synchrotron X-ray diffraction analysis reveals that in-situ nitrogen strengthening of the pure Ti occurs during the reactive AM of Ti. Furthermore, the presence of a nitrogen solid solution leads to the formation of high-strength pure Ti (yield strength of ∼979 MPa and ultimate tensile strength of ∼1058 MPa, respectively). This material exhibits excellent uniform elongation (11%) due to strong work hardening caused by the interaction of interstitial elements and submicrostructure. The proposed reactive AM approach paves the way for in-situ strengthening of pure metals and alloys.

Understanding of the atomic-scale mechanisms of rejuvenation of bulk metallic glass still remains unclear. Here, using configurational entropy derived from X-ray experiments, authors show a clear picture of the relaxation process during annealing of a metallic glass.

Abstract Currently, predominant high‐performance permanent magnets contain rare‐earth elements. In the search for rare‐earth‐free alternates, body‐centered tetragonal Fe–Ni is notable. The ordering to form this phase from the usual cubic close‐packed Fe‐Ni is understood to be possible only below a critical temperature, commonly accepted to be 593 K. The ordering is first demonstrated by using neutron irradiation to accelerate atomic diffusion. The tetragonal phase, designated as the mineral tetrataenite, is found in Fe‐based meteorites, its formation attributed to ultra‐slow cooling. Despite many attempts with diverse approaches, bulk synthesis of tetrataenite has not been reported. Here it is shown that with appropriate alloy compositions, bulk synthesis of tetrataenite is possible, even in conventional casting at cooling rates 11‒15 orders of magnitude higher than in meteorites. The barrier to obtaining tetrataenite (slow ordering from cubic close‐packed to body‐centered tetragonal) is circumvented, opening a processing window for potential rare‐earth‐free permanent magnets. The formation of tetrataenite on industrially practicable timescales also throws into question the interpretation of its formation in meteorites and their associated cooling rates.

Numerical finite element method (FEM) calculation results reveal that the effective strain differs between the ductile Zr-based bulk metallic glass and brittle Hf-based bulk metallic glass (BMG) during rolling at room temperature. The current results demonstrated that the deformation mechanism of ductile Zr-based bulk metallic glass can be explained by perceptibility of multiple shear bands formation, however, the deformation mechanism of brittle Hf-based bulk metallic glass is represented by uniformly distribution of effective strain through overall specimen rather than localized into shear band. The variation of stress and the distribution of effective strain change significantly near the surface region of a Hf-based bulk metallic glass plate with increasing number of rolling passes. Under elasto-plastic deformation by cold rolling, the brittle Hf-based BMG has a thickness strain (εt) of −0.012, and the neutral effective strain (εeff) is 0.011 at the thickness direction, respectively. We present experimental confirmation that when the applied effective strain can be adjusted to below 1.1% during elasto-plastic deformation then even the brittle as-cast Hf-based BMG can be deformed up to 44% thickness reduction and 23% width expansion after multi-pass cold rolling without fracture by localization of shear stress.

Ni-free Ti-based bulk metallic glasses (BMGs) are promising for biomedical applications, thanks to their excellent biocompatibility and high corrosion resistance. BMGs can be shaped and patterned by viscous flow deformation using thermoplastic net-shaping. This work presents a novel strategy for thermoplastic net-shaping of Ti40Zr10Cu34Pd14Sn2 BMG. Instead of operating for a short time slightly above the glass transition temperature to avoid crystallization, the proposed method accepts the formation of nanocrystals and makes use of the lower viscosity of the supercooled liquid when processing above the glass transition temperature. Following this approach, Ti40Zr10Cu34Pd14Sn2 BMG is deformed from a rod to a thin disk, and patterns scaling from 5 μm to 300 μm are successfully created on the Ti-BMG surfaces, demonstrating the potential to create complex features for functional materials. Furthermore, after the thermoplastic net-shaping treatment, the Vickers hardness increases by 6% while the corrosion and passivation current density decrease by an order of magnitude. This work reveals that the BMGs can still be deformed and patterned via the thermoplastic net-shaping technique if the first crystallization event of the BMG systems is the formation of nanocrystals. Most importantly, this work reveals the possibility of processing a broad family of mediocre glass-forming systems and semi-crystalline composites via thermoplastic net-shaping.

This paper envisions Ti40Zr10Cu36Pd14 bulk metallic glass as an oral implant material and evaluates its antibacterial performance in the inhabitation of oral biofilm formation in comparison with the gold standard Ti–6Al–4V implant material. Metallic glasses are superior in terms of biocorrosion and have a reduced stress shielding effect compared with their crystalline counterparts. Dynamic mechanical and thermal expansion analyses on Ti40Zr10Cu36Pd14 show that these materials can be thermomechanically shaped into implants. Static water contact angle measurement on samples' surface shows an increased surface wettability on the Ti–6Al–4V surface after 48 ​h incubation in the water while the contact angle remains constant for Ti40Zr10Cu36Pd14. Further, high-resolution transmission and scanning transmission electron microscopy analysis have revealed that Ti40Zr10Cu36Pd14 interior is fully amorphous, while a 15 ​nm surface oxide is formed on its surface and assigned as copper oxide. Unlike titanium oxide formed on Ti–6Al–4V, copper oxide is hydrophobic, and its formation reduces surface wettability. Further surface analysis by X-ray photoelectron spectroscopy confirmed the presence of copper oxide on the surface. Metallic glasses cytocompatibility was first demonstrated towards human gingival fibroblasts, and then the antibacterial properties were verified towards the oral pathogen Aggregatibacter actinomycetemcomitans responsible for oral biofilm formation. After 24 ​h of direct infection, metallic glasses reported a >70% reduction of bacteria viability and the number of viable colonies was reduced by ∼8 times, as shown by the colony-forming unit count. Field emission scanning electron microscopy and fluorescent images confirmed the lower surface colonization of metallic glasses in comparison with controls. Finally, oral biofilm obtained from healthy volunteers was cultivated onto specimens' surface, and proteomics was applied to study the surface property impact on species composition within the oral plaque.

We introduce five new biocompatible Ti-based metallic glass (MG) compositions with different metalloid and soft metal content for a synergistic improvement in corrosion properties. Without any potentially harmful elements such as Cu, Ni or Be, these novel alloys can eliminate the risk of inflammatory reaction when utilized for permanent medical implants. Excluding Cu, Ni or Be, which are essential for Ti-based bulk MG production, on the other hand, confines the glass-forming ability of novel alloys to a moderate level. In this study, toxic-element free MG alloys with significant metalloid (Si–Ge–B, 15–18 at.%) and minor soft element (Sn, 2–5 at.%) additions are produced in ribbon form using conventional single-roller melt spinning technique. Their glass-forming abilities and their structural and thermal properties are comparatively investigated using X-ray diffraction (XRD), synchrotron XRD and differential scanning calorimetry. Their corrosion resistance is ascertained in a biological solution to analyze their biocorrosion properties and compare them with other Ti-based bulk MGs along with energy dispersive X-ray. Ti60Zr20Si8Ge7B3Sn2 and Ti50Zr30Si8Ge7B3Sn2 MG ribbons present a higher pitting potential and passivation domain compared with other Ti-based MG alloys tested in similar conditions. Human mesenchymal stem cell metabolic activity and cytocompatibility tests confirm their outstanding cytocompatibility, outperforming Ti-Al6-V4.

Highly effective yet affordable non-noble metal catalysts are a key component for advances in hydrogen generation via electrolysis. The synthesis of catalytic heterostructures containing established Ni in combination with surface NiO, Ni(OH)2, and NiOOH domains gives rise to a synergistic effect between the surface components and is highly beneficial for water splitting and the hydrogen evolution reaction (HER). Herein, the intrinsic catalytic activity of pure Ni and the effect of partial electrochemical oxidation of ultra-smooth magnetron sputter-deposited Ni surfaces are analyzed by combining electrochemical measurements with transmission electron microscopy, selected area electron diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy. The experimental investigations are supplemented by Density Functional Theory and Kinetic Monte Carlo simulations. Kinetic parameters for the HER are evaluated while surface roughening is carefully monitored during different Ni film treatment and operation stages. Surface oxidation results in the dominant formation of Ni(OH)2, practically negligible surface roughening, and 3–5 times increased HER exchange current densities. Higher levels of surface roughening are observed during prolonged cycling to deep negative potentials, while surface oxidation slows down the HER activity losses compared to as-deposited films. Thus, surface oxidation increases the intrinsic HER activity of nickel and is also a viable strategy to improve catalyst durability.

Transformation-induced plasticity is a fundamental solution for improving the ductility of bulk metallic glass composites (BMGCs). However, the underlying mechanism remains controversial. Here, by using in situ transmission electron microscopy, we present direct observation of the transformation dynamics from β/ω phase to α’ phase of the crystalline dendrites in a TiZrCuBe BMGC under uniaxial tensile deformation. The transformation redistributes the stress in the adjacent matrix, making interfacial regions potential preferential sites for shear band nucleation. The high density of nucleation sites is believed to promote the formation of shear band networks and enhance the ductility of BMGCs.

The effects of severe plastic deformation (SPD) by means of high-pressure torsion (HPT) on the structural properties of the two iron-based metallic glasses Fe73.9Cu1Nb3Si15.5B6.6 and Fe81.2Co4Si0.5B9.5P4Cu0.8 have been investigated and compared. While for Fe73.9Cu1Nb3Si15.5B6.6, HPT processing allows us to extend the known consolidation and deformation ranges, HPT processing of Fe81.2Co4Si0.5B9.5P4Cu0.8 for the first time ever achieves consolidation and deformation with a minimum number of cracks. Using numerous analyses such as X-ray diffraction, dynamic mechanical analyses, and differential scanning calorimetry, as well as optical and transmission electron microscopy, clearly reveals that Fe81.2Co4Si0.5B9.5P4Cu0.8 exhibits HPT-induced crystallization phenomena, while Fe73.9Cu1Nb3Si15.5B6.6 does not crystallize even at the highest HPT-deformation degrees applied. The reasons for these findings are discussed in terms of differences in the deformation energies expended, and the number and composition of the individual crystalline phases formed. The results appear promising for obtaining improved magnetic properties of glassy alloys without additional thermal treatment.

Nanocomposites bear the potential to enable novel material properties that considerably exceed the capabilities of their individual constituent phases, thereby enabling the exploration of white areas on material property charts [...]

The intrinsic properties and the damage behavior of powder metallurgy (P/M) connecting rod preform have significant effects on its metal flow behavior during flashless forging into its final complex shape with substantial densification. The P/M material constitutive equation were established using isothermal compression tests, and then used to study the metal flow behavior of a P/M connecting rod preform during flashless forging based on finite element modelling (FEM). Moreover, the preform geometry was designed based on these metal flow mechanisms. Experiments and flashless forging of P/M connecting rod preforms were performed in order to verify the accuracy of the simulations. The simulated results are well consistent with the experimental results. Results showed that the shank is much more prone to cracking due to the higher deformation rate and the faster cooling rate. The optimal dimensions of the P/M preform were obtained. When the preform geometry are optimized, the average density of the connecting rod increases homogeneously, and becomes superior to that of the original shape. This work suggests that the geometry of the preform can be designed efficiently based on our models. This work can help to derive a P/M connecting rod preform optimization methodology, which can offer the possibility of improving the quality of the connecting rods efficiently. Keywords: Connecting rod, Numerical simulation, Optimization, Powder metallurgy

Bulk metallic glasses (BMGs) have attracted wide interest, but their successful application is hindered by their low ductility at room temperature. Therefore, the use of composites of a BMG matrix with crystalline secondary phases has been proposed to overcome this drawback. In the present work we demonstrate the fabrication of a tailored BMG nanocomposite containing a high density of monodisperse nanocrystals with a size of around 20 nm using a combination of mechanical and thermal treatment of Cu36Zr48Al8Ag8 well below the crystallization temperature. Direct observations of the interaction of the nanocrystals with a shear band during in situ deformation in a transmission electron microscope demonstrate that the achieved nanocomposite has the potential to inhibit catastrophic fracture in tension. This demonstrates that a sufficient number of nanoscale structural heterogeneities can be a route towards BMG composites with superior mechanical properties.

High-energy ball milling and spark plasma sintering (SPS) are used to create high-strength Ti-25Nb-6Zr biomedical alloys with β structures. The Ti-25Nb-6Zr alloy microstructure and mechanical properties were examined as a function of the sintering temperatures. The results showed that as the sintering temperature was raised, the densification process was expedited, and the comprehensive mechanical characteristics increased at first, then dropped slightly. Moreover, under high temperatures, the fracture morphology of the Ti-25Nb-6Zr biomedical alloys exhibited more dimples, indicating enhanced plasticity of the material. Evaluating the mechanical properties of the Ti-25Nb-6Zr biomedical alloy sintered at 1623 K indicated a high compressive strength of 1678.4 ± 5 MPa and an elongation of 12.4 ± 0.5%. The strengthening mechanisms are discussed in terms of the formation and distribution of bcc-Ti in the matrix as well as the homogeneous distribution of Nb and Zr. This research presents a new method for fabricating Ti-25Nb-6Zr biomedical alloys with high strength and low modulus values. The theoretical grounds for the development of high-performance Ti-Nb-Zr alloys will be laid by detailed research of this technology and its strengthening mechanisms.

One way to rejuvenate metallic glasses is to increase their free volume. Here, by randomly removing atoms from the glass matrix, free volume is homogeneously generated in metallic glasses, and glassy states with different degrees of rejuvenation are designed and further mechanically tested. We find that the free volume in the rejuvenated glasses can be annihilated under tensile or compressive deformation that consequently leads to structural relaxation and strain-hardening. Additionally, the deformation mechanism of highly rejuvenated metallic glasses during the uniaxial loading–unloading tensile tests is investigated, in order to provide a systematic understanding of the relaxation and strain-hardening relationship. The observed strain-hardening in the highly rejuvenated metallic glasses corresponds to stress-driven structural and residual stress relaxation during cycling deformation. Nevertheless, the rejuvenated metallic glasses relax to a more stable state but could not recover their initial as-cast state.

The ladle nozzle is one of the most important components in metal smelting. The cracking phenomenon occurs due to excessive thermal stress, which seriously affects the performance and life of the ladle nozzle. In this paper, a new composite structure of ladle nozzle is proposed, which consists of two materials with different properties and costs. The thermal physical parameters of the material are measured by high temperature dynamic Young’s modulus test method, thermal expansion test and flashing method. Based on the new structural model of the composite ladle nozzle, finite element simulation is used to combine the material ontology model, contact mechanics model and heat transfer model to study the temperature and thermal stress distribution inside the composite structure of the ladle nozzle during the casting process by taking representative key points inside the ladle nozzle. There is a large temperature gradient in the area near the casting hole, and the farther away from the casting hole, the smaller the temperature change. The ladle nozzle structure was optimized and compared with the existing ladle nozzle structure. The results show that the optimized composite structure of the ladle nozzle has significantly lowered thermal stress extremes under thermal shock, while the thermal stress distribution tends to be more uniform, which can largely reduce the chance of crack generation. This study is of great significance for improving the reliability and service life of the ladle nozzle and reducing its production cost.

Iron-based bulk metallic glasses are remarkably plastic, but the origin of their plasticity remains challenging to isolate. Here, the authors use high resolution microscopy to show that nanocrystals are dispersed within the glass and form hard and soft zones that are responsible for enhancing ductility.

Displacive martensitic transformations through lattice distortion usually involve a change from one crystal structure to another. Here however, the authors “melt” metastable Ti alloys during cooling and show that a martensitic transformation can lead to the formation of an intragranular amorphous phase.

In this study, the wear behavior of a heat-treatable Al-7Si-0.5Mg-0.5Cu alloy fabricated by selective laser melting was investigated systematically. Compared with the commercial homogenized AA2024 alloy, the fine secondary phase of the SLM Al-Cu-Mg-Si alloy leads to a low specific wear rate (1.8 ± 0.11 × 10−4 mm3(Nm)−1) and a low average coefficient of friction (0.40 ± 0.01). After the T6 heat treatment, the SLM Al-Cu-Mg-Si alloy exhibits a lower specific wear rate (1.48 ± 0.02 × 10−4 mm3(Nm)−1), but a similar average coefficient of friction (0.34 ± 0.01) as the heat-treated AA2024 alloy. Altogether, the SLM Al-3.5Cu-1.5Mg-1Si alloy is suitable for the achievement of not only superior mechanical performance, but also improved tribological properties.

Complex phase transformations in β-stabilised titanium alloys can dramatically change their α and β microstructures, providing tailorability for aerospace or biomaterial applications. Here the authors show that Ti-Nb alloys exhibit giant thermal expansions and identify two new pathways that lead to α phase formation.

The current investigation presents a green mechanochemical procedure for the synthesis of a special kind of rubber-compatible organo-montmorillonite (OMMT) for use in the inner liner compound of tires. The compatibility character of the OMMT arises from the mechanochemical reaction of the raw bentonite mineral and gum rosin as some of the organic constituents of the inner liner composition. The monitoring of OMMT synthesis by various characterization techniques reveals that gum rosin gradually intercalates into the montmorillonite (MMT) galleries during milling and increases the interlayer spacing to 41.1 ± 0.5 Å. The findings confirm the simultaneous formation of single- or few-layered OMMT platelets with average sizes from the sub-micron range up to several micrometers during the milling process. The mechanical properties of the OMMT/rubber nanocomposite, such as tensile strength, tear resistance and elongation, present a good enhancement in comparison to the un-modified material. Moreover, the organo-modification of the inner liner composition also leads to a property improvement of about 50%.

Amorphous/crystalline nanolaminate composites have aroused extensive research interest because of their high strength and good plasticity. In this paper, the nanoindentation behavior of Cu64Zr36/Cu amorphous/crystalline nanolaminates (ACNLs) is investigated by molecular dynamics (MD) simulation while giving special attention to the plastic processes occurring at the interface. The load–displacement curves of ACNLs reveal small fluctuations associated with shear transformation zone (STZ) activation in the amorphous layer, whereas larger fluctuations associated with dislocations emission occur in the crystalline layer. During loading, local STZ activation occurs and the number of STZs increases as the indentation depth in the amorphous layer increases. These STZs are mostly located around the indenter, which correlates to the high stresses concentrated around the indenter. When the indenter penetrates the crystalline layer, dislocations emit from the interface of amorphous/crystalline, and their number increases with increasing indentation depth. During unloading, the overall number of STZs and dislocations decreases, while other new STZs and dislocations become activated. These results are discussed in terms of stress distribution, residual stresses, indentation rate and indenter radius.

The plasticity of metallic glasses depends largely on the atomic-scale structure. However, the details of the atomic-scale structure, which are responsible for their properties, remain to be clarified. In this study, in-situ high-energy synchrotron X-ray diffraction and strain-rate jump compression tests at different cryogenic temperatures were carried out. We show that the activation volume of flow units linearly depends on temperature in the non-serrated flow regime. A plausible atomic deformation mechanism is proposed, considering that the activated flow units mediating the plastic flow originate from the medium-range order and transit to the short-range order with decreasing temperature.

We directly determine the thermodynamic fragility index of two metallic glasses (Mg65Cu25Gd10 and Au49Cu26.9Si16.3Ag5.5Pd2.3) from fictive temperature shifts induced by a variation of the quenching rate using fast differential scanning calorimetry (FDSC). Recent chip calorimeters are able to achieve the cooling rates necessary to perform such an evaluation. For the Mg65Cu25Gd10 and Au49Cu26.9Si16.3Ag5.5Pd2.3 metallic glasses studied, we find very good agreement of the kinetic fragility index with literature data obtained by conventional calorimetry and rheology. The thermodynamic fragility indices are m=25.5 ± 1.5 for Mg65Cu25Gd10 and m=50.3 ± 2.3 for Au49Cu26.9Si16.3Ag5.5Pd2.3, respectively. The FDSC method discussed here allows for fast and reliable determination of the kinetic fragility of metallic glasses, and is thus competitive with high-frequency methods.

Abstract In this paper we report the effect of alloying elements on hydrogen storage properties of melt-spun Mg-based alloys. The base alloys Mg90Si10, Mg90Cu10, Mg65Cu35 (at%) were studied. We also investigated the effect of rare earths (using MM: mischmetal) and Al in Mg65Cu25Al10, Mg65Cu25MM10 and Mg65Cu10Al15MM10 alloys. All the melt-spun alloys without MM show a crystalline structure, and the Mg65Cu25MM10 and Mg65Cu10Al15MM10 alloys showed an amorphous and partially amorphous structure respectively. At 350˚C all the alloys had a crystalline structure during the hydrogen absorption-desorption tests. It was observed that Si and Cu in the binaries alloys hindered completely the activation of the hydrogen absorption. The partial substitution of Cu by MM or Al allowed activation. The combined substitution of Cu by MM and Al showed the best results with the fastest absorption and desorption kinetics, which suggests that this combination can be used for new Mg-alloys to improve hydrogen storage properties.

The microstructure and phase formation of rapid solidified Ag-rich Ag-Cu-Zr alloys were investigated. Two types of structure; interconnected- and droplet-type structures, were obtained due to phase separation mechanisms. The former was spinodal decomposition and the later was nucleation and growth mechanism. Depending on the alloy compositions, three crystalline phases; FCC-Ag, AgZr and Cu10Zr7 phases were observed along with an in-situ nanocrystalline/amorphous composite. Vickers hardness testing indicated a significant increase of hardness in the nanocrystalline/amorphous-composite alloy.

The microstructures and mechanical properties of (Cu0.5Zr0.5)100−xZnx (x = 0, 1.5, 2.5, 4.5, 7, 10, and 14 at. %) bulk metallic glass (BMG) composites were studied. CuZr martensitic crystals together with minor B2 CuZr and amorphous phases dominate the microstructures of the as-quenched samples with low Zn additions (x = 0, 1.5, and 2.5 at. %), while B2 CuZr and amorphous phases being accompanied with minor martensitic crystals form at a higher Zn content (x = 4.5, 7, 10, and 14 at. %). The fabricated Cu-Zr-Zn BMG composites exhibit macroscopically appreciable compressive plastic strain and obvious work-hardening due to the formation of multiple shear bands and the deformation-induced martensitic transformation (MT) within B2 crystals. The present BMG composites could be a good candidate as high-performance structural materials.

The laser-based powder bed fusion (LBPF) process or commonly known as selective laser melting (SLM) has made significant progress since its inception. Initially, conventional materials like 316L, Ti6Al4V, and IN-718 were fabricated using the SLM process. However, it was inevitable to explore the possible fabrication of the second most popular structural material after Fe-based alloys/steel, the Al-based alloys by SLM. Al-based alloys exhibit some inherent difficulties due to the following factors: the presence of surface oxide layer, solidification cracking during melt cooling, high reflectivity from the surface, high thermal conductivity of the metal, poor flowability of the powder, low melting temperature, etc. Researchers have overcome these difficulties to successfully fabricate the different Al-based alloys by SLM. However, there exists no review dealing with the fabrication of different Al-based alloys by SLM, their fabrication issues, microstructure, and their correlation with properties in detail. Hence, the present review attempts to introduce the SLM process followed by a detailed discussion about the processing parameters that form the core of the alloy development process. This is followed by the current research status on the processing of Al-based alloys and microstructure evaluation (including defects, internal stresses, etc.), which are dealt with on the basis of individual Al-based series. The mechanical properties of these alloys are discussed in detail followed by the other important properties like tribological properties, fatigue properties, etc. Lastly, an outlook is given at the end of this review.