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Refractory high entropy alloys (RHEAs) with multiple principal elements constitute a new paradigm in alloy design and have gained recent interest for advanced technical applications due to their unique properties and mechanical stability at high temperatures. However, the refractory metals that make up these alloys are pretty expensive, and they cause RHEAs to exhibit low plasticity behaviour at room temperature. The high stability properties of RHEAs from room temperature to high temperatures limit their machinability with traditional cutting methods. Therefore, it is vitally important to economically machine these alloys while preserving their mechanical properties and minimising waste. For this purpose, in this study, the machinability of a HfTaTiVZr RHEA was evaluated with wire electric discharge machining (WEDM). The surface morphology, crack formation, and mechanical characteristics of the surface layer were investigated as a function of three different cutting conditions: rough cutting, semi-finishing, and finishing. The RHEA was precision cut in three passes by reducing the volume of material in each pass, resulting in better surface quality with the optimal cutting speed and metal removal rate. However, rough cutting gave better results than semi-finish and finished cutting processes in preserving mechanical properties.

Refractory high-entropy alloys (RHEAs) have recently attracted widespread attention due to their outstanding mechanical properties at elevated temperatures, making them appealing for concentrating solar power and nuclear energy applications. Here, the corrosion behavior of equimolar HfTaTiVZr and TaTiVWZr RHEAs was investigated in molten FLiNaK eutectic salt (LiF-NaF-KF: 46.5−11.5−42 mol.%) at 650 °C. Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and immersion test measurements were carried out for these two RHEAs and compared with Inconel 718 (IN718) superalloy and SS316 stainless steel under identical test conditions. Both TaTiVWZr and HfTaTiVZr refractory high-entropy alloys exhibited an order of magnitude lower corrosion rate than SS316. IN718 and TaTiVWZr showed similar corrosion rates. Corrosion products enriched with noble alloying elements formed in the case of TaTiVWZr and IN718 were stable and protective on the substrate. SS316 showed the lowest corrosion resistance and void formation along the exposed surface due to the active dissolution of Cr and Fe, which provided diffusion paths for the corroded species. The surface analysis results showed that IN718 underwent pitting corrosion, while TaTiVWZr experienced selective dissolution in the inter-dendritic area. In contrast, HfTaTiVZr and SS316 experienced corrosion at the grain boundaries.

Lightweight energy-saving magnesium (Mg) nanocomposites could be titled materials of future. Remarkable specific strength along with acceptable ductility is two key features of these materials which have made them a unique class of emerging materials. However, magnesium nanocomposites are at the initial stages of development and therefore systematic research is required to establish microstructure/property relationships at different potential conditions (i.e. temperatures and strain rates). In this paper, a recently introduced magnesium-samarium oxide (Mg–Sm2O3) nanocomposite, with different volume fractions of nanosize Sm2O3 particles as reinforcement, is employed to study ambient temperature rate-dependent plastic response of the material. To study the rate-dependent response of the materials, a depth-sensing nanoindentation measurement technique was used which is considered a non-destructive, robust, and convenient method to assess the controlling mechanisms of creep phenomenon in small scales. Tests were performed on both nanocomposites and pure Mg for the purpose of comparison. Microstructural observations and nanoindentation data indicate that the creep resistance of the materials is directly associated with the volume fraction of the nanoparticles. The results of this study would provide the required reference lines for the forthcoming elevated temperature creep assessment of the materials.

Metallic glasses exhibit excellent properties such as ultrahigh strength and excellent wear and corrosion resistance, but there is limited understanding on the relationship between their atomic structure and mechanical properties as a function of their structural state. In this paper, we bridge the processing-structure-property gap by utilizing molecular dynamics simulation for a model binary metallic glass, namely Ni80P20. The structural statistics including the fraction of Voronoi index, the distribution of Voronoi volume, and medium-range ordering are calculated to explain the observed changes in mechanical behavior and strain localization upon relaxation and rejuvenation. Our findings demonstrate that the evolution of mechanical properties can be linked to the atomic structure change in terms of short- and medium-range ordering. With the help of structural statistics, the mechanical properties are determined based on simple Voronoi analysis.

The effect of ion irradiation on the hardness and yield strength of Zr57Nb5Cu15.4Ni12.6Al10 bulk metallic glass has been studied using nanoindentation and micropillar compression tests. The results for the amorphous alloy were compared with those for 304 stainless steel. After Ni2+ ion irradiation, the metallic glass was found on an average to have 16% lower hardness and 13% lower yield strength. In contrast, 304 stainless steel showed significant hardening (~ 50% hardness and strength increase) after irradiation under identical conditions. The irradiation-induced hardening of the steel was attributed to hindrance of dislocation movement from the defects generated, while the softening behavior of the metallic glass was attributed to structural change in the irradiated region while retaining a fully amorphous state. The present work paves the way for better understanding of the irradiation response of metallic glasses to develop degradation-resistant alloys for next-generation nuclear applications.

The strain gradient plasticity of multiprincipal element alloys, CoCrNi and CoCrFeMnNi, was investigated in work-hardened and annealed conditions using nano-indentation. The hardness of the alloys demonstrated significant dependence on indentation depth, which was explained by geometrically necessary dislocations resulting from the high strain gradients due to the shape of the indenter. The characteristic length-scale of the indentation size effect for the multiprincipal element alloys was found to be larger than pure nickel due to higher friction stress, which constrains the storage volume of geometrically necessary dislocations.

Hypereutectoid SAE 52100 steel is extensively used in bearing applications. Microstructure modification in terms of dislocation martensite and carbide refinement was achieved for SAE 52100 steel through a simple duplex heat treatment. Refinement of prior austenite grains to less than 5 μm resulted in the conversion of conventional high-carbon twinned martensite to dislocation martensite. The concurrent refinement of austenite grains and carbide precipitates was accomplished by high-temperature austenitization followed by low-temperature tempering. This resulted in nanoscale nonstoichiometric e-carbides within a heavily twinned martensitic structure. These nanoscale carbides acted as grain boundary pinning agents after their transformation to θ-carbides during the final austenitization process. The resulting microstructure was characterized by a fine dispersion of θ-carbides within dislocation martensite and showed roughly 24% increase in tensile strength and 30% better wear resistance compared to conventional structure.

Metallic glasses are a unique class of materials combining ultrahigh strength together with plastic-like processing ability. However, the currently used melt quenching route to obtain amorphous alloys has a high cost basis in terms of manufacturing and expensive constituent elements often necessary to achieve the glassy state, thus hindering widespread adoption. In contrast, multimaterial electrodeposition offers a low-cost and versatile alternative to obtain amorphous alloys. Here, we demonstrate multiscale manufacturing of a model binary amorphous system by a facile and scalable pulsed electrodeposition approach. The structural and mechanical characteristics of electrodeposited Ni-P metallic glasses are investigated by a combination of experiments and molecular dynamics simulations. The property dependence on slight change in alloy chemistry is explained by the fraction of short-range-order clusters and geometrically unfavorable motifs. Bicapped square antiprism polyhedra clusters with two-atom connections result in more homogeneous deformation for Ni

Complex concentrated alloys with multiple principal elements represent a new paradigm in alloy design by focusing on the central region of a multi-component phase space and show a promising range of properties unachievable in conventional alloys [...]

An integrated experimental and molecular dynamics approach was used for developing low-activation high entropy alloys, potentially attractive for next generation nuclear reactor applications. These alloys were based on the concept of high entropy phase formation from a palette of elements with intrinsic low activity, namely Ta–Ti–V–Zr–X (X = Hf or W), with constituents in equimolar proportions. Molecular dynamics predicted homogenous alloy formation for Ta–Ti–V–Zr–Hf. In contrast, a tendency for Ta–W atomic-pair clustering was seen for Ta–Ti–V–Zr–W, in agreement with microstructure after melt-casting and homogenization. Both alloys showed stable microstructure with high hardness, which was retained up to 300 °C.

The reciprocating sliding wear behavior of two high entropy alloys, CoCrFeMnNi and Al0.1CoCrFeNi, was evaluated in dry and marine environments. Both the alloys showed better wear performance in marine environment as compared to dry condition, indicating negative synergy of wear and corrosion. Al0.1CoCrFeNi was more wear resistant compared to CoCrFeMnNi in both environments. Accelerated electrochemical corrosion tests were carried out to quantify the effect of passive layer on marine wear behavior. Al0.1CoCrFeNi showed lower corrosion rate, higher pitting resistance and greater degree of passivation. A strong correlation was found between the electrochemical polarization resistance and wear resistance.

An Al 0.25 Ti 0.75 CoCrFeNi high entropy alloy (HEA), consisting of multiple principal elements, forms the uncommonly observed chi-phase, which is a large lattice parameter intermetallic phase based on the body centered cubic crystal structure, as the matrix phase and a L2 1 phase (ordered Huesler phase, X 2 YZ-type based on the face-centered cubic structure) as a major secondary phase. Additionally, a face centered cubic phase with a high density of nano-twins is also present in the microstructure as a third phase. The extremely high Vicker's hardness of the matrix chi phase (1090Hv ± 14) and of the L2 1 phase (570 ± 9 H V ) along with low sliding coefficient of friction (∼0.3) and low wear rate (∼1.2 × 10 −5 mm 3 /N m) makes this HEA a promising candidate for mechanical wear-resistant applications.

Laser engineered net shaping (LENS) processing of an in-situ Ti-B4C composite, results in the natural formation of a novel periodically layered structure, when a mixture of Ti powders and B4C powders are used as a feedstock. One of the layers predominantly consisted of TiB2 and inter-dendritic TiC phases, while the other alternating layer exhibited a rather complex microstructure, comprising of TiB, TiC, partially melted-B4C and α-Ti phases. Increasing the laser power (300–700 W) results in an increase in the height/thickness of these layers, as well as the number density of in-situ formed ceramic precipitates (TiB, TiC) in the TiB + TiC + α-Ti layer. Additionally, the Heipel-Roper theory of weld pool dynamics was employed to rationalize the unconventional microstructural evolution in these multi-layered LENS processed Ti-B4C composites. Microhardness and wear properties revealed that among the three powers, the 700 W condition exhibited the best combined wear and hardness which can be attributed to reduced porosity, and an increase in hardness of both layered regions due to an increase in number density of precipitates in the TiB + TiC + α-Ti layer. Such AM process induced naturally layered composites open up a new avenue for design and development of hybrid materials for future engineering applications.

Amorphous metallic alloys are widely used in bulk form and as coatings for their desirable corrosion and wear behavior. Nevertheless, the effects of heat treatment and thermal cycling on these surface properties are not well understood. In this study, the corrosion and wear behavior of two Zr-based bulk metallic glasses were evaluated in as-cast and thermally relaxed states. Significant improvement in wear rate, friction coefficient, and corrosion penetration rate was seen for both alloys after thermal relaxation. A fully amorphous structure was retained with thermal relaxation below the glass transition. There was an increase in surface hardness and elastic modulus for both alloys after relaxation. The improvement in surface properties was explained based on annihilation of free volume.

Metallic glass nanocomposite thin films were synthesized for an immiscible Ag-Cu alloy system by magnetron sputtering. The structure of the films was unique, consisting of homogeneously dispersed nanocrystallites in an amorphous matrix. The size and volume fraction of the nanocrystallites increased with increasing film thickness resulting in increased elastic modulus and hardness. The high electrical conductivity of the nanocomposite films was examined by a valence-band study, which showed that exchange interaction between Ag and Cu in the nanocomposite structure resulted in enhanced charge carrier concentration. The inverse correlation between electrical conductivity and film thickness was explained by surface and interface scattering of electrons with increasing volume fraction of nanocrystallites. The small temperature dependence of conductivity was attributed to the distorted Fermi surface of the nanocomposite films resulting in a greater contribution from structure scattering, which is temperature-independent.

CoCrFeMnNi high entropy alloys (HEAs) were additively manufactured (AM) by laser powder bed fusion and their corrosion resistance in 3.5 wt% NaCl solution was studied by potentiodynamic polarization and electrochemical impedance spectroscopy tests. A systematic study of AM CoCrFeMnNi HEAs&rsquo, porosity under a wide range of laser processing parameters was conducted and a processing map was constructed to identify the optimal laser processing window for CoCrFeMnNi HEAs. The near fully dense AM CoCrFeMnNi HEAs exhibit a unique non-equilibrium microstructure consisting of tortuous grain boundaries, sub-grain cellular structures, columnar dendrites, associated with some processing defects such as micro-pores. Compared with conventional as-cast counterpart, the AM CoCrFeMnNi HEAs showed higher pitting resistance (&Delta, E) and greater polarization resistance (Rp). The superior corrosion resistance of AM CoCrFeMnNi HEAs may be attributed to the homogeneous elemental distribution and lower density of micro-pores. Our study widens the toolbox to manufacture HEAs with exceptional corrosion resistance by additive manufacturing.

Al–Co–Cr–Fe high-entropy alloy coatings were laser additively produced on aluminum substrate under different laser fluences (17.0–21.2 J/mm2). The resultant coatings consisted of a mixture of high-entropy and intermetallic phases, which resulted in marked improvement in hardness (~ 275–500 HV) as compared to the aluminum substrate (~ 30 HV). Coating corresponding to higher laser fluences showed lower corrosion currents (Icorr ~ 3.6 × 10−4 mA/cm2) and higher linear polarization resistance (LPR) of ~ 14–16 kΩ/cm2 as compared to the aluminum substrate (Icorr ~ 7×10−4 mA/cm2) and ~ 11 kΩ/cm2 in 0.6 M NaCl solution. The behavior of surface properties was analyzed in relation to the variation in fraction of HEA and intermetallic phases within the coatings resulting due to increased content of Al from the Al substrate with an increase in the laser fluence. The coating consisting of optimal amount of HEA and intermetallic phases showed a tenfold decrease wear volume loss (0.01 mm3) as compared to Al substrate showing 0.11 mm3.

The electrodeposition route to obtain amorphous alloys offers a facile, low-cost, and versatile alternative to conventional melt quenching. However, there are significant knowledge gaps in tribological properties and wear mechanisms for electrodeposited metallic glasses (EMGs). Here, the wear behavior and the scratch response of a model binary amorphous alloy system were investigated. Electrodeposited Ni–P metallic glasses were systematically studied as a function of composition, with amorphous alloy formation over the narrow range of 10 at% to 20 at% phosphorus. The electrodeposited metallic glasses showed hardness values in the range of 6.6–7.4 GPa, modulus in the range of 155–163 GPa, and friction coefficient around 0.50. Among the studied alloys, electrodeposited Ni80P20 showed the lowest wear rate, which was two orders of magnitude lower than electrodeposited pure Ni. The wear mechanism was determined to be extensive plastic deformation along with mild ploughing, micro tears, and formation of discontinuous lubricious oxide patches. Scratch tests showed an increase in critical load for damage initiation with the increase in phosphorus content among the amorphous alloys following the trend: Ni80P20 > Ni85P15 > Ni90P10. The overall wear rate for the electrodeposited metallic glasses was found to be lower than most reported bulk metallic glasses (BMGs). This represents a fundamental study on structure-property correlations in electrodeposited metallic glasses and demonstrates the versatility of electrodeposition in tuning the surface properties of amorphous alloys.

This paper reports the dynamic elastic constants of laser powder bed fusion additively manufactured Ti6Al4V alloy by recently developed effective bulk modulus elastography technique and compares them with the static elastic constants evaluated using the nanoindentation technique. With this elastography technique, two ultrasound frequencies (10 MHz and 20 MHz) were employed, which distinctly identified spatially varying the dynamic elastic constants and effective density in additively manufactured Ti6Al4V while comparing to the wrought Ti6Al4V. The spatial resolution of elastic constants and effective density of the scanned region significantly improved at 20 MHz ultrasound frequency. The dynamic elastic constants were 5 % –8 % lower than static elastic constants obtained for the additively manufactured Ti6Al4V and wrought Ti6Al4V. In addition, the present study compares the elastic moduli of additively manufactured Ti6Al4V, wrought Ti6Al4V, and solutionized and water quenched wrought Ti6Al4V. The microstructural examination of additively manufactured Ti6Al4V using scanning electron microscopy revealed a high density of internal twins within martensite laths contrary to scarcely twinned martensite lath in water quenched wrought Ti6Al4V. The origin of such high defect density was realized by a thermo-mechanical computational model that predicted rapidly changing alternating tensile-compressive stresses in the range of 49–720 MPa that, in turn, affected the dynamic and static elastic constants.

The mechanical behavior of nano-scale metallic glasses was investigated by in situ compression tests in a scanning electron microscope. Platinum-based metallic glass nano-pillars were fabricated by thermoplastic forming. The nano-pillars and corresponding bulk substrate were tested in compression over the range of room temperature to glass transition. Stress–strain curves of the nano-pillars were obtained along with in situ observation of their deformation behavior. The bulk substrate as well as nano-pillars showed an increase in elastic modulus with temperature which is explained by diffusive rearrangement of atomic-scale viscoelastic units.

Bulk metallic glass matrix composites represent a unique microstructural design strategy for overcoming the strength/ductility trade-off in structural alloys. Site-specific mechanical behavior of a Ti-based bulk metallic glass composite was evaluated at microstructural length-scale. The micro-pillars on the amorphous matrix showed an average yield point of 1.9 GPa followed by serrated plastic deformation characteristic of shear banding. In contrast, micro-pillars on the crystalline dendritic phase showed a much lower yield strength of 0.72 GPa on average for the four different crystallographic orientations chosen, smooth plastic flow with no recognizable load burst, and stable strain-hardening after yield point. A number of micro-pillars were made at the interface between the glassy matrix and the crystalline dendrite. The mixed micro-pillars showed homogeneous deformation and greater plasticity which was attributed to their smaller stored elastic energy. Shear bands initiated in the amorphous matrix were arrested by the crystalline dendrite, which accommodated plasticity through slip bands and dislocations pile-ups. The interface remained intact after plastic deformation, with no observable signs of devitrification in the amorphous phase.

Evolution of atomic distribution during devitrification of a zirconium-based bulk metallic glass, Zr41.2Ti13.8Cu12.5Ni10.0Be22.5, was investigated using three-dimensional atom probe microscopy. Atom probe analysis showed uniform distribution of constituent elements for the as-cast alloy, with no phase separation. The metallic glass was annealed at different temperatures to study the crystallization pathways and the length scale, distribution, and morphology of the phases formed. Devitrification was found to proceed via the formation of a metastable icosahedral phase. The devitrification pathway is explained based on “strong-liquid” behavior of this alloy.

Friction stir processing of a ternary immiscible alloy was investigated as a pathway to thermally stable nanostructured alloys. The processed alloy was characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM), nano-indentation, and thermal stability analysis. Both XRD and high-magnification SEM confirmed the formation of solid solution at the shear edge of the friction stir layer. Microstructural inhomogeneity was observed in the processed region that resulted in hardness variation. Upon annealing treatment, a significant improvement in hardness was observed at 200°C that was due to the formation of nano-precipitates. Remarkably, the Cu-Ag-Nb immiscible system displayed exceptional thermal stability up to 500°C.

Temperature-induced variation in magnetic properties for cobalt-based metallic glass was investigated. The formation of metastable nanocrystalline phases prior to complete devitrification and their effect on magnetic properties for Co72B19.2Si4.8Cr4 metallic glass was studied. The nature, shape, and distribution of the intermediate nanocrystalline phases were characterized using transmission electron microscopy and x-ray diffraction. A drastic change in magnetic properties was found in going from a fully amorphous state to different stages of nanocrystallization. The coercivity changes from amorphous soft magnetic state (H c ~ 0.12 Oe) to a nanocrystalline-dispersed hard magnetic state (H c ~ 187 Oe), with no significant change in saturation magnetization. This suggests potential use in futuristic magnetic switches, fluxgate sensors, and electromagnetic shielding devices.

The nanomechanical behavior of the Co20Cr20Fe20Mn20Ni20 high-entropy alloy was investigated in as-cast, rolled, annealed, and thin-film forms. Dislocation nucleation was studied by repeated indents at a low load for each of the different processing conditions. Distinct displacement bursts (pop in) were observed in the loading curve marked by incipient plasticity for all the samples. The as-cast and annealed samples showed pop ins for 100% of the indents, whereas the rolled and thin-film samples showed a much lower fraction of displacement bursts. This was explained by the high density of dislocations for the cold-worked and thin-film conditions. The strong depth dependence of hardness was explained by geometrically necessary dislocations. The nanomechanical behavior and twinned microstructure indicate low stacking-fault energy for this high-entropy alloy.

The authors report on the high catalytic activity and bi-functional catalysis mechanism of amorphous metals in degrading AZO Dye, a toxic water pollutant and carcinogen. Aluminum-based metallic glass was found to completely degrade AZO dye at room temperature without any toxic by-products. The high catalytic activity originates from the simultaneous ionization of the transition metals, which act as electron donors for rapid degradation of AZO dye in an aqueous medium. The dye degradation rate and catalytic activity were characterized via UV–VIS absorption spectroscopy. The rate of dye degradation was significantly faster compared to state-of-the-art zero valent iron. The dye degradation mechanism was studied using Raman and IR spectroscopy combined with X-ray photoelectron spectroscopy.

The crystallization behavior and viscosity of an in situ metallic glass composite was investigated using a non-contact electrostatic levitation technique. The width of the supercooled liquid region for the amorphous matrix was found to be 74 K, indicating its excellent stability against crystallization. The viscosity data follows the Vogel–Fulcher–Tammann relation, which was used to determine the fragility of the composite melt. The viscosity of the composite is compared to monolithic metallic glasses in the context of “strong-fragile” liquid behavior.

Substrate-cell interactions for a bioimplant are driven by substrate's surface characteristics. In addition, the performance of an implant and resistance to degradation are primarily governed by its surface properties. A bioimplant typically degrades by wear and corrosion in the physiological environment, resulting in metallosis. Surface engineering strategies for limiting degradation of implants and enhancing their performance may reduce or eliminate the need for implant removal surgeries and the associated cost. In the current study, we tailored the surface properties of stainless steel using submerged friction stir processing (FSP), a severe plastic deformation technique. FSP resulted in significant microstructural refinement from 22 μm grain size for the as-received alloy to 0.8 μm grain size for the processed sample with increase in hardness by nearly 1.5 times. The wear and corrosion behavior of the processed alloy was evaluated in simulated body fluid. The processed sample demonstrated remarkable improvement in both wear and corrosion resistance, which is explained by surface strengthening and formation of a highly stable passive layer. The methylthiazol tetrazolium assay demonstrated that the processed sample is better in supporting cell attachment, proliferation with minimal toxicity, and hemolysis. The athrombogenic characteristic of the as-received and processed samples was evaluated by fibrinogen adsorption and platelet adhesion via the enzyme-linked immunosorbent assay and lactate dehydrogenase assay, respectively. The processed sample showed less platelet and fibrinogen adhesion compared with the as-received alloy, signifying its high thromboresistance. The current study suggests friction stir processing to be a versatile toolbox for enhancing the performance and reliability of currently used bioimplant materials.

Structural changes in a bulk metallic glass subjected to high-strain plastic deformation was investigated. A zirconium-based bulk metallic glass was friction stir processed at different tool rotational speeds. The alloy retained its fully amorphous structure at lower speed. At higher tool rotational speed there was partial nano-crystallization with nearly three times increase in surface hardness. Changes in the glass transition temperature, relaxation and crystallization enthalpies were analyzed to explain the physics of high-strain deformation in amorphous metals.

In recent years, there is great interest in development of “reduced activity” refractory alloys for next generation nuclear applications for safe and efficient post-service recycling. Here, the strain rate sensitivity of a refractory high entropy alloy, namely HfTaTiVZr, was investigated consisting of all reduced activation elements. The intrinsic versus extrinsic effects in rate sensitivity were evaluated for fundamental understanding of the differences in loading condition. Uniaxial bulk and micro-pillar compression tests were performed along with multi-axial nano-indentation in a wide range of strain rates. The extrinsic strain rate sensitivity obtained from micro-pillar compression and bulk compression was higher than its intrinsic characteristic determined from nano-indentation. The low value of strain rate sensitivity obtained from nano-indentation was attributed to greater degree of dislocation entanglement in confined volume beneath the indenter. On the other hand, the high value of strain rate sensitivity in case of micro-pillar compression tests was attributed to the extrinsic effect of larger surface to volume ratio which helped in annihilation of dislocations through the free surface. A pronounced indentation size effect of strain rate sensitivity was also observed. At smaller depth, higher mobility and diffusion of dislocations near the free surface resulted in higher strain rate sensitivity compared to that at larger indentation depth.

Friction stir processing (FSP) was carried out for AE42 Mg alloy resulting in significant grain refinement and uniform dispersion of fine in situ precipitates. The average grain size was 20 μm for the as-cast AE42 alloy, which was refined to 1.5 μm after FSP. Tensile testing revealed significantly higher modulus and yield strength for the friction stir processed (FSPed) specimen with some improvement in ductility. The fractured surface of the as-cast alloy showed ridges, grooves and cracks indicating brittle failure. In contrast, the fractured surface of FSPed specimen showed fine dimples, characteristic of ductile failure. Nano-indentation was used to analyze the variation of hardness and modulus across the nugget zone of the FSPed specimen. FSPed specimen demonstrated greater strain-hardening tendency compared to the as-cast alloy. Enhancing the mechanical properties of Mg alloys can result in substantial cost savings across a number of industries and have wide economic impact.

The liquid impingement erosion behavior of a zirconium-based bulk metallic glass (BMG), Zr44Ti11Cu10Ni10Be25, was evaluated in this study. For comparison, commonly used hydroturbine steel was evaluated under the same test conditions. BMG demonstrated more than four times higher resistance against cavitation erosion compared with hydroturbine steel. The unusually high erosion resistance for BMG is attributed to its uniform amorphous structure with no grain boundaries, higher hardness, and ability to accommodate strain through localized shear bands.

The wettability of different nanotextured metallic glass surfaces is investigated. Wettability is quantified by the sessile drop technique using a distilled water droplet. It is demonstrated that hydrophilic–hydrophobic nature of the metallic glass surface can be controlled through nanotopography. The contact angle was found to increase from 70° for the flat metallic glass surface to 110° for a nanorod patterned surface. The difference in contact angle is explained in terms of the surface topography/roughness measured using atomic force microscopy.

Friction stir processing (FSP) of Mg based AE42 alloy was performed under single pass as well as double pass conditions. The evolution of microstructure was investigated using electron back scatter diffraction (EBSD) analysis. EBSD revealed that the grain size and texture varies within the nugget zone of friction stir processed region. The variation of mechanical properties across the nugget region was evaluated using nanoindentation. Hardness and Young's modulus was found to increase along the depth of the friction stir processed specimen. This was attributed to a finer grain structure with increasing depth. The friction stir processed specimen showed higher tendency toward strain hardening compared to as-cast alloy. Understanding microstructure–property relationship paves the way for optimization of FSP conditions and development of advanced functional Mg alloys.

High-performance magnetic materials have immense industrial and scientific importance in wide-ranging electronic, electromechanical, and medical device technologies. Metallic glasses with a fully amorphous structure are particularly suited for advanced soft-magnetic applications. However, fundamental scientific understanding is lacking for the spin-exchange interaction between metal and metalloid atoms, which typically constitute a metallic glass. Using an integrated experimental and molecular dynamics approach, we demonstrate the mechanism of electron interaction between transition metals and metalloids. Spin-exchange interactions were investigated for a Fe-Co metallic glass system of composition [(Co1-x Fe x )0.75B0.2Si0.05]96Cr4. The saturation magnetization increased with higher Fe concentration, but the trend significantly deviated from simple rule of mixtures. Ab initio molecular dynamics simulation was used to identify the ferromagnetic/anti-ferromagnetic interaction between the transition metals and metalloids. The overlapping band-structure and density of states represent 'Stoner type' magnetization for the amorphous alloys in contrast to 'Heisenberg type' in crystalline iron. The enhancement of magnetization by increasing iron was attributed to the interaction between Fe 3d and B 2p bands, which was further validated by valence-band study.

Bulk metallic glasses (BMGs) are fully amorphous multi-component alloys with homogeneous and isotropic structure down to the atomic scale. Some attractive attributes of BMGs include high strength and hardness as well as excellent corrosion and wear resistance. The research goal of this paper is to determine the mechanical properties at elevated temperatures. To accomplish this goal, we have used two methods in this paper to determine the Young's modulus of a BMGs, Zr41.2Ti13.8Cu12.5Ni10Be22.5 at elevated temperatures: sonic resonance method and nanoindentation. In the sonic resonance method, the system was designed using a laser displacement sensor to detect the sonic vibration produced by a speaker on the specimen in high-temperature furnace. The Young'ss modulus was found to reduce from 100 GPa (350°C) to 94 GPa (50°C). In the nanoindentation method, modulus was determined from the unloading curve and found to be in the same range as measurements from sonic resonance technique.

There has been tremendous interest in recent years in a new class of multi-component metallic alloys that are referred to as high entropy alloys, or more generally, as complex concentrated alloys. These multi-principal element alloys represent a new paradigm in structural material design, where numerous desirable attributes are achieved simultaneously from multiple elements in equimolar (or near equimolar) proportions. While there are several review articles on alloy development, microstructure, mechanical behavior, and other bulk properties of these alloys, then there is a pressing need for an overview that is focused on their surface properties and surface degradation mechanisms. In this paper, we present a comprehensive view on corrosion, erosion and wear behavior of complex concentrated alloys. The effect of alloying elements, microstructure, and processing methods on the surface degradation behavior are analyzed and discussed in detail. We identify critical knowledge gaps in individual reports and highlight the underlying mechanisms and synergy between the different degradation routes.

Electrochemical devices such as fuel cells, electrolyzers, lithium-air batteries, and pseudocapacitors are expected to play a major role in energy conversion/storage in the near future. Here, it is demonstrated how desirable bulk metallic glass compositions can be obtained using a combinatorial approach and it is shown that these alloys can serve as a platform technology for a wide variety of electrochemical applications through several surface modification techniques.

The atomic distribution in catalytically active metallic glass alloys, Pd43Cu27Ni10P20and Pt57.5Cu14.7Ni5.3P22.5, was investigated using three-dimensional atom probe microscopy. Atom probe analysis showed uniform distribution of constituent elements for both the starting amorphous alloys, with no phase separation. Both the crystallized alloys showed eutectic microstructure with a very sharp interface (~0.5 nm as determined from atom probe). The atomic distribution in the devitrified state is explained based on the “fragile liquid” behavior for these noble-metal glassy alloys.

Activation energy and diffusion kinetics are important in modulating the high temperature oxidation behavior of metals. Recently developed multi-principal element alloys, also called high entropy alloys (HEAs), are promising candidate material for high temperature applications. However, the activation energies and diffusion kinetics of HEAs have been limitedly explored. We investigate the diffusional activation energy for oxidation of Al0.1CoCrFeNi HEA. Compared to conventional steels and Ni-based super alloys, the HEA showed a significantly higher diffusion activation energy. This behavior is explained based on low potential energy of the lattice and interstitial sites which effectively trap the atoms, limiting their diffusion. The atomic mean jump frequency for interstitial diffusion of oxygen in the HEA is four-orders of magnitude lower than T22 and T91 steels and seven-orders of magnitude lower compared to pure iron. Al0.1CoCrFeNi HEA showed the lowest oxidation rate compared to conventionally used steels, super-alloys, and coatings.

We demonstrate the refinement and uniform distribution of the crystalline dendritic phase by friction stir processing (FSP) of titanium based in situ ductile-phase reinforced metallic glass composite. The average size of the dendrites was reduced by almost a factor of five (from 24 μm to 5 μm) for the highest tool rotational speed of 900 rpm. The large inter-connected dendrites become more fragmented with increased circularity after processing. The changes in thermal characteristics were measured by differential scanning calorimetry. The reduction in crystallization enthalpy after processing suggests partial devitrification due to the high strain plastic deformation. FSP resulted in increased hardness and modulus for both the amorphous matrix and the crystalline phase. This is explained by interaction of shear bands in amorphous matrix with the strain-hardened dendritic phase. Our approach offers a new strategy for microstructural design in metallic glass composites.