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Bulk metallic glasses--formed by supercooling the liquid state of certain metallic alloys--have potentially superior mechanical properties to crystalline materials. Here, we report a Co(43)Fe(20)Ta(5.5)B(31.5) glassy alloy exhibiting ultrahigh fracture strength of 5,185 MPa, high Young's modulus of 268 GPa, high specific strength of 6.0 x 10(5) Nm kg(-1) and high specific Young's modulus of 31 x 10(6) Nm kg(-1). The strength, specific strength and specific Young's modulus are higher than previous values reported for any bulk crystalline or glassy alloys. Excellent formability is manifested by large tensile elongation of 1,400% and large reduction ratio in thickness above 90% in the supercooled liquid region. The ultrahigh-strength alloy also exhibited soft magnetic properties with extremely high permeability of 550,000. This alloy is promising as a new ultrahigh-strength material with good deformability and soft magnetic properties.

A different dependence of apparent glass-forming ability (GFA) on casting-atmosphere pressure is observed in a Zr65Al7.5Ni10Cu17.5-xPdx (x=0–17.5) alloy system. Low-Pd alloys (x<12.5) reveal low GFA dependence, while high-Pd ones (x>=12.5) show high GFA dependence on atmosphere pressure applied during casting. The phenomenon is suggested to originate from the fact that for the high-Pd alloys, the transformation region of supercooled-liquid to quasicrystalline phase is located at the low-temperature side of the undercooled-liquid region where the atmosphere-pressure dependence of cooling characteristic coincidently takes place. The on-cooling phase transformation in the alloy system and the cooling mechanism during mold-casting process are discussed comprehensively. [ABSTRACT FROM AUTHOR]

Zr65Al7.5Ni10Cu12.5Nb5 glass was found to exhibit a large plastic compressive strain of over 10% and the property was suggested to be due to deformation-induced nanocrystallization. A transmission electron microscopic observation, however, only revealed obscure ordered clusters with a size of ˜2 nm in the fracture surface of a deformed sample, instead of well-identified crystals as previously reported for the Zr–Al–Ni–Cu–Pd system. This phenomenon is suggested to correlate with the higher viscosity of supercooled liquid and the slower grain growth of icosahedral phase during primary crystallization in the Zr65Al7.5Ni10Cu12.5Nb5 compared to those in the Zr65Al7.5Ni10Cu12.5Pd5 alloy. The role of the deformation-induced nanoclusters on the enhanced compressive plasticity was discussed. [ABSTRACT FROM AUTHOR]

The high-entropy alloy (HEA) design strategy is effective for ultra-coarsening-resistant 3D interconnected materials developed by liquid metal dealloying (LMD). However, the fundamental understanding of the dealloying mechanism and structural evolution of multi-principal elements 3D structured materials is still missing. In this study, the microstructural evolutions of 3D interconnected HEAs in Mg matrix were investigated using two types of multiphase precursors, namely, arc-melted and homogenized ones. The precursors' microstructure greatly influences dealloying kinetics and dealloying mechanisms what, in its turn, determines the final morphology of the 3D interconnected HEAs in Mg matrix. First, the prior fcc phase was dealloyed faster than any other precursor phases at dealloying temperatures from 600 to 900 °C. Second, the dealloying kinetics was faster along precursor grain boundaries (GB) as compared with grain interior. This led to the formation of a unique layered composite structure due to the inhomogeneous dealloying along the fine lamellars' GB of the homogenized precursor. Moreover, governing orientation relationship between precursor and dealloying product depends on the LMD conditions, and it significantly affects the 3D interconnected grain structure. The fundamental understanding of the dealloying mechanisms will pave the way for customized morphology design of the 3D interconnected HEAs in metallic matrix with improved thermal stability and physical properties. [Display omitted] [ABSTRACT FROM AUTHOR]

A new type of Mg-Zn-Cu-Gd-based alloy strengthened by quasicrystal and Laves phase was developed. This alloy exhibits much better creep properties compared to AE42(Mg-4 wt% Al-2 wt% rare-earth) alloy, which is the benchmark creep-resistant magnesium die-casting alloy under the compressive creep condition of 180°C and 80 MPa. The new alloy also exhibits high room-temperature mechanical properties close to that of AZ91 alloy. The good mechanical properties are attributed to the special microstructure; the thermally stable icosahedral quasicrystals phase (i-phase) and Laves phase distributed along the grain boundary as a hard skeleton, and some fine β′1 precipitates distributed homogenously on the matrix. The dislocation morphology after the creep test was studied, and the strengthening mechanism was proposed. [ABSTRACT FROM AUTHOR]

Abstract: Multi-component (Cu0.50Hf0.35Ti0.10Ag0.05)100− x Ta x (x =0, 1, 3, 5, 8, 12) bulk metallic glass (BMG) composites containing in situ formed dendrites were prepared successfully. With increasing Ta content, both compressive fracture strength (σ f) and elastic-plastic strain (ε f) increase from 2180MPa and 2.1% for x =0, to 2770MPa and 19.2% for x =8, respectively, but yield strength and elastic modulus decrease. The precipitation of a high volume fraction of the dendrites (V dendrite) causes the compositional variation of the dendrites and its counterpart glass matrix. Composition analysis shows that both Hf and Ti elements exhibit an opposite behavior of dissolving into the dendrites during the cooling. About 7–11at.% component elements (Ti, Cu and Ag) were detected in Ta-rich dendrites, but no Hf element was found. With increasing V dendrite, the content of component elements dissolving into Ta-rich dendrites decreases from 11.35at.% for V dendrite =4.3% and 7.97at.% for V dendrite =26.5%. Indentation testing was also performed to evaluate the properties of the composites. With increasing V dendrite, the hardness of the dendrites decreases from 6.0GPa for x =3 to 5.21GPa for x =12, and its elastic modulus increases from 151.2GPa for x =3 to 156.9GPa for x =12. The hardness and elastic modulus of the glassy matrix also decrease, respectively, from 9.66 and 148.7GPa for x =0 to 9.36 and 137.4GPa for x =12 with increasing precipitation of the dendrites. The variation of the properties is due to the compositional change originating from the opposite behavior of Hf and Ti elements to dissolve into the dendrites. [Copyright &y& Elsevier]

The primary transformation reaction of the Zr65Al7.5Cu27.5 ternary glassy alloy with a low oxygen impurity of approximately 100 mass ppm was investigated. We have discovered the precipitation of the metastable icosahedral phase with a fine grain size of 50-100 nm in diameter accompanying with the formation of stable Zr2Cu phase at the annealing temperatures ranging from 715 to 730 K. The lattice spacing of Zr2Cu phase decreases at higher temperatures, which is attributed to the rearrangement of Zr and Cu in the decomposition of the icosahedral phase. It is suggested that the formation of the icosahedral phase in the primary stage originates from the existence of the quenched-in icosahedral local atomic configuration in the glassy state. [ABSTRACT FROM AUTHOR]

It is found that an increase in the hydrostatic chamber pressure (P) during the casting process suppresses the glass forming ability (GFA) of the Zr65Al7.5Ni10Cu17.5 alloy, on the contrary, it enhances the GFA of the Zr65Al7.5Ni10Pd17.5 alloy. This opposite dependence of the GFA on P in these alloys may be because the volume increases or decreases by the primary crystallization. [Copyright &y& Elsevier]

The structure of an arc-melted ingot of Ti 70 Fe 15 Co 15 alloy has been studied by X-ray diffractometry and scanning electron microscopy. Its microstructure consists of a primary P m m Ti(Fe, Co) phase and a binary Ti(Fe, Co) + I m m β-Ti solid solution eutectic. The mechanical properties were tested by an Instron-type machine. A sample cut from the central part of the ingot exhibits excellent mechanical properties. [ABSTRACT FROM AUTHOR]

The structure and mechanical properties of Mg-Zn-Al-Y base cast alloys containing an icosahedral quasicrystal phase (i-phase) as a main strengthening phase were investigated. Mg-8Zn--4Al-xY base bulk alloys containing the i-phase were prepared by casting into a copper mold at moderate cooling rates. The Y addition was effective for decreasing the size of the i-phase and the increasing the homogeneity of its dispersed state. The mechanical properties examined by compression tests at room temperature were much superior to those of a conventional AZ91 Mg alloy. The creep tests at elevated temperatures indicated a promising high temperature creep resistance of the quasicrystal-reinforced Mg-Zn-Al-Y cast alloy. The strengthening mechanism was also discussed. [ABSTRACT FROM AUTHOR]

The mechanical properties, glass-forming ability, supercooled liquid region and devitrification behaviour of the Cu–Zr–Ti–(Pd, Ag, Pt and Au) bulk glass formers were studied by using a mechanical testing machine, X-ray diffraction, transmission electron microscopy, differential scanning calorimetry and isothermal calorimetry. The bulk glassy alloys of diameter 2 mm were formed in the Cu55Zr30Ti10Pd5 and Cu55Zr30Ti10Ag5 alloys while Cu55Zr30Ti10Au5 bulk alloy showed mixed glassy and crystalline structure. No glassy phase was formed in the Cu55Zr30Ti10Pt5 bulk alloy whereas the glassy phase was formed in all of the ribbon samples prepared by rapid solidification. The studied alloys except for the Pt-bearing one have slightly increased compressive fracture or yield strength values compared to ternary Cu60Zr30Ti10 glassy alloy. At the same time Pd and Au addition significantly expand the supercooled liquid region of Cu–Zr–Ti glassy alloy and increase Young''s modulus. A nanoicosahedral phase is primarily formed in the Cu55Zr30Ti10(Pd,Au)5 glassy alloys in the initial stage of the devitrification process by nucleation and three-dimensional diffusion-controlled growth. Nearly the same quasilattice constant obtained in the Cu55Zr30Ti10(Pd,Au)5 alloys illustrates the same type of the icosahedral phase in these alloys. However, no icosahedral phase was found in the Cu55Zr30Ti10(Ag,Pt)5 alloys. [Copyright &y& Elsevier]

High-entropy alloys (HEAs) have attracted extensive interest due to their unprecedented structure and mechanical performance. We recently proposed a series of novel corich twinning induced plasticity (TWIP) and transformation induced plasticity (TRIP) HEAs with superior tensile properties at room temperature; however, the hot deformation behavior has not been reported. Here, we investigated the dynamic recrystallization behavior and grain refinement of a representative TRIP-HEA, compressed at temperatures of 1123–1273 K with strain rates of 0.1–0.001 s−1. We characterized the impact of the temperature and strain rate on the grain structure evolution. A constitutive equation was constructed to reveal the correlations between the flow stress, strain rate, temperature, and strain. The apparent activation energy was estimated to be ~385.7 kJ/mol. The discontinuous dynamic recrystallization played an important role in the grain refinement, particularly at a relatively higher temperature and a lower strain rate, and the volume fraction and morphology of the recrystallized grains exhibited a strong dependency on the Zener–Hollomon parameter. The study provides guidelines for the grain refinement of HEAs through thermomechanical processing. [ABSTRACT FROM AUTHOR]

High-entropy nanomaterials possessing high accessible surface areas have demonstrated outstanding catalytic performance, beating that found for noble metals. In this communication, we report about the synthesis of a new, nanoporous, high-entropy alloy (HEA) possessing open porosity. The nanoporous, high-entropy Ta19.1Mo20.5Nb22.9V30Ni7.5 alloy (at%) was fabricated from a precursor (TaMoNbV)25Ni75 alloy (at%) by liquid metal dealloying using liquid magnesium (Mg). Directly after dealloying, the bicontinuous nanocomposite consisting of a Mg-rich phase and a phase with a bulk-centered cubic (bcc) structure was formed. The Mg-rich phase was removed with a 3M aqueous solution of nitric acid to obtain the open, porous, high-entropy Ta19.1Mo20.5Nb22.9V30Ni7.5 alloy (at%). The ligament size of this nanoporous HEA is about 69 ± 9 nm, indicating the high surface area in this material. [ABSTRACT FROM AUTHOR]

The CoCrNi and precipitate-hardened (CoCrNi)94Ti3Al3 medium entropy alloys (MEAs) have attracted much attention, due to their exceptional mechanical properties, whereas the hot deformation characteristics have not been revealed. In the present study, we investigated the dynamic recrystallization behavior and microstructure evolutions of the two MEAs hot-compressed at single-phase temperatures. The constitutive equation was obtained, and microstructures were observed. Discontinuous dynamic recrystallization acted as a key mechanism of grain refinement at a relatively higher temperature and lower strain rate, which leads to the formation of a homogeneous grain structure. The addition of Ti and Al promoted dynamic recrystallization due to the solid solution hardening effect. The results provide valuable guidelines for microstructure refinement via thermomechanical processing. [ABSTRACT FROM AUTHOR]

Abstract: In the glassy temperature region from ambient to the glass transition temperature (T g), an apparent Young''s modulus (E ap), the slope of the initial linear part on the stress–strain curve, in a Zr-based metallic glass clearly depends on both temperature and strain rate, especially above 0.87 T g. This indicates that viscous contribution is included in this apparent elastic response. If yield strain is deduced with Young''s modulus measured by the ultrasonic vibration method, which excludes the viscous contribution, temperature dependence of the yield strain can be captured well with the Argon''s Shear Transformation Zone (STZ) model. On the other hand if the yield strain is deduced with E ap, the strain was found to keep the “universal” critical value ∼0.020 for many metallic glasses at the ambient temperature. This may indicate another clue to understand the yield mechanism on BMG. [Copyright &y& Elsevier]

Surface functionalization is an effective approach to change the surface properties of a material to achieve a specific goal such as improving the biocompatibility of the material. Here, the surface of the commercial biomedical Ti-6Al-7Nb alloy was functionalized through synthesizing of a porous surface layer by liquid metal dealloying (LMD). During LMD, the Ti-6Al-7Nb alloy is immersed in liquid magnesium (Mg) and both materials react with each other. Particularly, aluminum (Al) is selectively dissolved from the Ti-6Al-7Nb alloy into liquid Mg while titanium (Ti) and niobium (Nb) diffuse along the metal/liquid interface to form a porous structure. We demonstrate that the porous surface layer in the Ti-6Al-7Nb alloy can be successfully tailored by LMD. Furthermore, the concentration of harmful Al in this porous layer is reduced by about 48% (from 5.62 ± 0.11 wt.% to 2.95 ± 0.05 wt.%) after 30 min of dealloying at 1150 K. The properties of the porous layer (e.g., layer thickness) can be tuned by varying the dealloying conditions. In-vitro tests suggest improved bone formation on the functionalized porous surface of the Ti-6Al-7Nb alloy. [ABSTRACT FROM AUTHOR]

Rising demand for bone implants has led to the focus on future alternatives of alloys with better biocompatibility and mechanical strength. Thus, this research is dedicated to the synthesis and investigation of new compositions for low-alloyed Ti-based compounds, which conjoin relatively acceptable mechanical properties and low elastic moduli. In this regard, the structural and mechanical properties of α + β Ti-Fe-Cu-Sn alloys are described in the present paper. The alloys were fabricated by arc-melting and tilt-casting techniques which followed subsequent thermo-mechanical treatment aided by dual-axial forging and rolling procedures. The effect of the concentrations of the alloying elements, and other parameters, such as regimes of rolling and dual-axial forging operation, on the microstructure and mechanical properties were thoroughly investigated. The Ti94Fe1Cu1Sn4 alloy with the most promising mechanical properties was subjected to thermo-mechanical treatment. After a single rolling procedure at 750 °C, the alloy exhibited tensile strength and tensile plasticity of 1300 MPa and 6%, respectively, with an elastic modulus of 70 GPa. Such good tensile mechanical properties are explained by the optimal volume fraction balance between α and β phases and the texture alignment obtained, providing superior alternatives in comparison to pure α- titanium alloys. [ABSTRACT FROM AUTHOR]

Titanium carbide (TiC), is the most thermodynamically stable compound in the Ti–C–Cu system, which makes it a suitable reinforcement phase for copper matrix composites. In this work, the interaction of a Ti–Cu alloy with different forms of carbon was investigated to trace the structural evolution leading to the formation of in-situ TiC–Cu composite structures. The reaction mixtures were prepared from Ti25Cu75 alloy ribbons and carbon black or nanodiamonds to test the possibilities of obtaining fine particles of TiC using ball milling and Spark Plasma Sintering (SPS). It was found that the behavior of the reaction mixtures during ball milling depends on the nature of the carbon source. Model experiments were conducted to observe the outcomes of the diffusion processes at the alloy/carbon interface. It was found that titanium atoms diffuse to the alloy/graphite interface and react with carbon forming a titanium carbide layer, but carbon does not diffuse into the alloy. The diffusion experiments as well as the synthesis by ball milling and SPS indicated that the distribution of TiC particles in the composite structures obtained via reactive solid-state processing of Ti25Cu75+C follows the distribution of carbon particles in the reaction mixtures. This justifies the use of carbon sources that have fine particles to prepare the reaction mixtures as well as efficient dispersion of the carbon component in the alloy–carbon mixture when the goal is to synthesize fine particles of TiC in the copper matrix. [ABSTRACT FROM AUTHOR]

Even though the Mg-based bulk metallic glasses (BMGs) have shown superior anti-corrosion properties compared with their crystalline counterparts, the brittleness of them limits the widespread application of these materials. In the present study, we have firstly introduced porous NiTi shape memory alloy particles into an Mg-Zn-Ca BMG by the direct adding method. This composite showed both improved compressive strength and corrosion resistance in Hank's solutions than its monolithic glassy counterpart. The NiTi dispersoids among the matrix were likely to hinder the main shear band propagation, and also acted as the corrosion barriers. Furthermore, the porous nature of present added particle could further increase the interface areas, which should enhance the reinforcing effects compared with solid ones. This low-cost, high-anticorrosive composite was a good candidate as an engineering material. [ABSTRACT FROM AUTHOR]

In the present letter we compare the thermal conductivities of Cu- and Ni-based alloys in relation with their cooling rates and glass-forming abilities. The cooling rates obtained for Cu- and Ni-based bulk glass-forming alloys are found to scale with the thermal conductivities of the base elements. Relatively low thermal conductivity of Ni-based alloy compared to the Cu-based one explains its lower glass-forming ability. The results also indicate that the thermal conductivity of the molten alloy should be also used as an indicator of the glass-forming ability among the other factors. [ABSTRACT FROM AUTHOR]

The relatively low density of Ti (4.5 Mg/m3) implies high strength/density ratio for Ti-based alloys. A composite Ti65Fe35 alloy produced in the shape of arc-melted ingot of about 20 mm in diameter and 10 mm in height exhibits a high mechanical strength of 2.2 GPa at 6.7% ductility and a Young’s modulus of 149 GPa. Its microstructure consists of the cubic TiFe phase and a supersaturated BCC β-Ti solid solution. The formation of a supersaturated β-Ti solid solution and the disperse eutectic structure obtained result in a high strength of the Ti–Fe alloy which in addition to that has much higher ductility compared to that of nanostructured and glassy alloys. The Ti–Fe alloy is characterized by low cost of the alloying elements and does not require an additional injection mould casting procedure. [Copyright &y& Elsevier]

Nanoporous non-noble metals with attractive properties can be fabricated by liquid metal dealloying (LMD). However, further refinement of the ligament size of nanoporous metals produced by LMD is desired because this high-temperature process induces rapid ligament coarsening. Herein, we fabricate nanoporous refractory metals and alloys by LMD. The molybdenum (Mo)-tantalum (Ta) alloy with the smallest ligament size of the specimens contains a B2 ordered structure, whereas the other specimens possess disordered structures. It is proposed that the B2 ordering of the Mo-Ta alloy suppresses ligament coarsening by restricting the surface diffusion of atoms during LMD. The Mo-Ta alloy with B2 ordered structure exists in a previously inaccessible low-temperature region of the related phase diagram, illustrating that LMD can enable access to new materials. Our results indicate that materials with refined ligaments may be obtained by LMD promoting the formation of ordered structures. [Display omitted] [ABSTRACT FROM AUTHOR]

The viscosity and flow stress of a bulk Pd[sub 40]Ni[sub 10]Cu[sub 30]P[sub 20] alloy glass near the glass transition were measured as a function of temperature and strain rate under compression. The steady-state viscosity of the glass for a given temperature remains constant at low strain rate, then decreases by many orders of magnitude above a critical strain rate. A master curve in term of the viscosity ratio η/η[sub N] and the product η[sub N]ε. has been constructed, where η and η[sub N] are, respectively, the steady-state viscosity and Newtonian viscosity, and ε. is the strain rate. The flow stress also can be represented in terms of the product η[sub N]ε.. The master curves are fitted with a simple stress relaxation of the form 1-exp[-t/λ] with t=ε.[sup -1]. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: The effect of Mo addition on the glass-forming ability (GFA), magnetic properties, mechanical properties and corrosion resistance of (Fe0.76Si0.096B0.084P0.06)100−x Mo x (x =0, 2, 4 and 6at.%) bulk glassy alloys (BGAs) with high Fe contents was investigated. The 2at.% Mo addition makes the alloy composition approach towards a eutectic point, which could result in an increase in the GFA. The BGA rod with diameters up to 3.5mm was produced by copper mold casting. These BGAs exhibit a rather high saturation magnetization of 0.98–1.51T and lower coercive force of 1.7–2.1A/m. A significant improvement in corrosion resistance was observed with microalloying Mo element in 1N H2SO4 solution. Furthermore, these Fe-based BGAs show super-high strength of ∼3.3GPa and Young''s modulus of 200GPa. [Copyright &y& Elsevier]

Abstract: The high strength metastable Ti–Fe–Co alloys were produced by arc-melting in the shape of distorted semi-spherical ingots with the dimensions of about 25–30mm in diameter and 7–10mm in height. The structure of the hypereutectic Ti–Fe–Co alloys (at Fe/Co ratio ≥1) studied by X-ray diffractometry and scanning electron microscopy consisted of the primary dendrites of an ordered cP2 Ti(Fe, Co) compound and an eutectic consisting of the cP2 Ti(Fe, Co) compound and a disordered BCC cI2 β-Ti solid solution. The strongest Ti–Fe–Co alloys have a hypereutectic structure and exhibit a high strength exceeding 2000MPa and a plastic deformation of about 15%. The quaternary Ti67Fe14Co14Sn5 alloy exhibits a high strength of 1830MPa and the largest plastic strain of 24%. The deformation behavior and the fractography of Ti–Fe–Co and Ti–Fe–Co–Sn alloys are studied in detail. The formation of a composite-like structure with hard carcass of the intermetallic phase in the relatively soft eutectic matrix enabled both high strength and ductility. The accommodation deformation can be explained by the intergranular sliding of the primary Ti(Fe, Co) dendrites in the softer eutectic matrix. Rough primary dendrites and eutectic rods of the cP2 intermetallic phase act as efficient barriers for shear strain and cracks propagation, while fine eutectic rods of submicron size are quite effortlessly cut by deformation bands and cracks. It is shown that the high strength and ductility values for Ti-based alloys can be achieved without using the injection mould casting or rapid solidification procedure. [Copyright &y& Elsevier]

Face-centered cubic (fcc)-phase high-entropy alloys (HEAs) have attracted much academic interest, with the stacking fault energy (SFE) playing an important role in regulating their mechanical behaviors. Here, we revealed the principles for regulating both the elastic and plastic behaviors by composition modification and Mo addition in an fcc-phase quaternary CoCrFeNi system with the assistance of ab initio and thermodynamics calculations. An increase in Co content and a decrease in Fe and Ni contents reduced the fcc phase stability and SFE, but enhanced the elastic modulus, anisotropy, and lattice friction stress. A minor substitution of Co by Mo increased the lattice constant, but decreased the SFE and elastic modulus. Based on these findings, we developed a series of strong and ductile metastable fcc-phase Co x Cr 25 (FeNi) 70- x Mo 5 (x = 30, 40, 50) HEAs with mechanical properties superior to those of the CoCrFeNi HEAs. The careful investigation revealed that the enhanced mechanical properties are due to the Mo-addition-induced strengthening accompanied with a low-SFE-induced restriction of planar behavior of dislocations, mechanical twinning, and strain-induced martensitic transformation. The findings shed light on the development of high-performance HEAs. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Abstract The equiatomic CoCrMnNiFe high-entropy alloy (HEA) has attracted much attention owing to its exceptional mechanical properties. Here, we designed novel face-centered cubic (fcc) phase Co-rich non-equiatomic CoCrMnNiFe HEAs with tensile properties superior to the counterparts, derived from lowering stacking fault energy (SFE) via modifying constituent concentrations. The decrease of Mn, Ni, Fe meanwhile increase of Co, Cr concentrations does reduce the SFE value, based on ab initio and thermodynamics calculations. Hereinto, Co 35 Cr 20 Mn 15 Ni 15 Fe 15 and Co 35 Cr 25 Mn 15 Ni 15 Fe 10 HEAs overcame the strength-ductility trade-off, contributing to twinning-induced plasticity (TWIP) or transformation-induced plasticity (TRIP) effects, respectively. The present study sheds light on developing high performance HEAs. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Metallic glass (MG) exhibits viscous flow behavior in the supercooled liquid (SCL) state, which is of great advantage for its net-forming process. However, the viscous workability varies strongly with the alloy system and/or composition. In this paper, we demonstrate how MG with less viscous workability such as Gd-based MG can be processed in the SCL region. Based on this understanding, high aspect ratio analyzer gratings of 9 μm pitch and ∼30 μm heights have been fabricated through an imprinting method by allowing crystallization during a rapid heating isochronal imprinting process. The analyzer gratings made of Gd-based MG have brought a breakthrough for advancing neutron phase imaging based on grating interferometer. [ABSTRACT FROM AUTHOR]

• Si-addition overcomes the strength-ductility trade-off of CoCrFeNi HEA. • Si-addition tunes the plastic deformation mechanism of the CoCrFeNi HEA. • Si-addition enhances yield stress by multiple strengthening mechanisms. • The plasticity mechanism is tuned partially due to the reduced SFE. Face-centered cubic single-phase high-entropy alloys (HEAs) containing multi-principal transition metals have attracted significant attention, exhibiting an unprecedented combination of strength and ductility owing to their low stacking fault energy (SFE) and large misfit parameter that creates severe local lattice distortion. Increasing both strength and ductility further is challenging. In the present study, we demonstrate via meticulous experiments that the CoCrFeNi HEA with the addition of the substitutional metalloid Si can retain a single-phase FCC structure while its yield strength (up to 65%), ultimate strength (up to 34%), and ductility (up to 15%) are simultaneously increased, owing to a synthetical effect of the enhanced solid solution strengthening and a reduced SFE. The dislocation behaviors and plastic deformation mechanisms were tuned by the addition of Si, which improves the strain hardening and tensile ductility. The present study provides new strategies for enhancing HEA performance by targeted metalloid additions. [ABSTRACT FROM AUTHOR]

• Hall-Petch coefficient of FCC-phase HEAs increases with the decrease of SFE. • Elastic modulus accounts for high intrinsic yield strengths of Co-rich HEAs. • Faulting, twinning/phase transformation enhances the strength of Co-rich HEAs. The equiatomic CoCrFeMnNi Cantor alloy, a face-centered-cubic (FCC) single-phase high-entropy alloy (HEA), has attracted considerable attention owing to its high strength and good ductility over a wide temperature range. The mechanical performance of this alloy was improved by reducing the stacking fault energy (SFE) through composition modification, and thus, a series of near- or non-equiatomic HEAs that are stronger and more ductile than their predecessor have been developed. However, the plastic-deformation behavior and strengthening mechanisms have not yet been fully discovered. In this study, we investigated the yielding and hardening behaviors of the Cantor alloy and FCC-phase Co-rich HEAs with different SFEs by in situ neutron diffraction combined with the first-principles method and electron-microscopy characterizations. The Co-rich HEAs exhibited a higher intrinsic yield strength than the Cantor alloy, mainly because of the larger shear modulus or modulus misfit, and grain refinement being more effective in improving the yield strength of low-SFE HEAs. Furthermore, higher flow stresses and better ductility of the Co-rich HEAs are attributed to the greater dislocation density and a larger number of stacking faults, which enhanced the strain-hardening rate during tensile deformation. The low SFE promoted mechanical twinning, and martensitic transformation contributed to higher strain-hardening rates. The present study provides deep insight into the yielding and hardening of FCC-phase HEAs, the understanding of which is a prerequisite for developing high-performance materials. [ABSTRACT FROM AUTHOR]

Near-equiatomic single-phase twining-induced plasticity (TWIP) high-entropy alloys (HEAs) exhibit a good combination of strength and ductility, but their modest yield strength requires further improvement. Here, we propose a strategy for markedly enhancing their strength while retaining satisfactory ductility, taking advantage of the temperature dependence of the stacking fault energy. The room-temperature strength of a representative TWIP HEA was improved by the cryogenic pre-deformation-induced dislocations, martensite, nanotwins, and stacking faults. The tensile properties were further tuned by subsequent annealing to obtain partially recovered or recrystallized microstructures. The influence of regulated microstructures on the yield strength was clarified by neutron diffraction line profile analysis. The room temperature tensile yield strength of the HEA increased from 275 to 1012 MPa while retaining an elongation of 21.9%. The yield strength and elongation were then further altered to 826.9 MPa and 42.6%. This study presents possibilities for fabricating advanced HEAs by tuning the substructures. [Display omitted] [ABSTRACT FROM AUTHOR]

The kinematic and isotropic hardening behavior was investigated for high and medium entropy alloys with a single-phase face-centered cubic (FCC) structure. The cross-slip associated with screw dislocations in FCC structures is strongly influenced by local fluctuations in the spatial distribution of different atom species. The local atomic arrangements inhibit the movement of Shockley partial dislocations during plastic deformation, thereby lowering the probability of cross-slip and generating a higher back-stress. This study used a solid-solution induced back-stress model, which combines nonlinear kinematic and isotropic hardening, to investigate the effects of dislocation forest stress and back-stress in a non-equiatomic Cr 12 Fe 42 Mn 24 Ni 22 medium entropy alloy. Based on the experimental results, numerical simulations by the finite element method were performed to validate this modeling approach. [ABSTRACT FROM AUTHOR]

[Display omitted] Recently-developed high-entropy alloys (HEAs) containing multiple principal metallic elements have extended the compositional space of solid solutions and the range of their mechanical properties. Here we show that the realm of possibilities can be further expanded through substituting the constituent metals with metalloids, which are desirable for tailoring strength/ductility because they have chemical interactions and atomic sizes distinctly different from the host metallic elements. Specifically, the metalloid substitution increases local lattice distortion and short-range chemical inhomogeneities to elevate strength, and in the meantime reduces the stacking fault energy to discourage dynamic recovery and encourage defect accumulation via partial-dislocation-mediated activities. These impart potent dislocation storage to improve the strain hardening capability, which is essential for sustaining large tensile elongation. As such, metalloid substitution into HEAs evades the normally expected strength-ductility trade-off, enabling an unusual synergy of high tensile strength and extraordinary ductility for these single-phase solid solutions. [ABSTRACT FROM AUTHOR]

Pure Ti shows promising performance for biomedical applications, but its strength needs to be greatly improved when used as heavy-load implants. In this work, β-Ti alloy was used as the reinforced layer to prepare Ti/β-Ti alloy laminated composite through Spark Plasma Sintering (SPS) with hot/cold rolling and partial recrystallization annealing. The microstructural evolution of Ti layer, β-Ti alloy layer and the interface between them during the fabrication process was investigated. The results showed the composite comprises alternating recrystallized Ti layer, β-Ti alloy layer with deformed microstructure, and α+β dual phase interface layer containing submicron sized rod-like or granular α phase. Besides, the deformation behavior and mechanical properties of the Ti/β-Ti alloy laminate composite were studied. The Ti/β-Ti alloy laminate composite after partial recrystallization annealing shows a good match of high strength and good ductility (tensile strength: 832 MPa and uniform elongation: 20%), owing to the co-work of the diffusion interface layer and the constraint effect. The α+β dual phase layer has an important effect on weakening the deformation incompatibility between Ti layer and β-Ti alloy layer and preventing crack propagation during the tensile deformation. [ABSTRACT FROM AUTHOR]

Medium-entropy alloys strengthened by the L1 2 -type coherent precipitates were recently proposed, whereas the mechanical property still needs to be improved. Here, we demonstrated a strategy for notably improving the strength of the representative (CoCrNi) 94 Ti 3 Al 3 alloy, in which the refinement of grain structures and the promotion of precipitation were concurrently achieved by pre-strain followed by aging. A refined grain structure containing incoherent σ-precipitates and a large number of coherent L1 2 -precipitates was formed, which enhances the yield strength and ultimate tensile strength up to 1431 MPa and 1683 MPa respectively. Furthermore, decreasing pre-strain temperature or increasing strain further aids the enhancement. The present study opens an avenue for fabricating high-performance precipitation-strengthened alloys. [ABSTRACT FROM AUTHOR]

We investigated the nanoscale anisotropic deformation behavior of Al-supersaturated α 2 -Ti 3 Al single crystals, using wedge indentation with the loading axis parallel to the (0001) α 2 basal plane. The deformability, plastic deformation mechanism, and introduced dislocation structures beneath the indentations were notably affected by the inclination angle between the indenter edge and basal plane. Notably, abnormal dislocation bands were introduced when the edge was parallel to the (0001) plane, which can potentially be utilized for manipulating the phase decomposition locally. The present study sheds light on the regulation of local plastic deformation and manipulation of nanoscale phase transformation in metals and alloys. Image 1 • The local deformation behavior of Al-supersaturated α 2 -Ti 3 Al single crystals was firstly investigated by wedge indentation. • The deformation behavior is notably affected by the orientation relationship between indenter and basal plane of crystal. • Regulated periodic basal dislocations for manipulating phase decompositions is successfully introduced. [ABSTRACT FROM AUTHOR]