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A NiTi/Mg composite was fabricated using a method that combines top-down pore-forming and pressureless infiltration processes. The phase constituents of this simple composite are B2-NiTi, B19′-NiTi and Mg phases. Both the size and the distribution of the Mg-phase are fine and homogeneous. The composite has very high mechanical strength and damping capacity, ~1.2 and 1.5-fold higher than those of a similar composite with different microstructures, respectively. These behaviors are generally attributed to the high damping capacity of Mg, the physical continuity of the composite, and the homogeneous distribution of fine Mg-phase, which generate more interfaces, contributing to the damping capacity. This composite is considered a good candidate for use as a damping material in engineering applications. [ABSTRACT FROM AUTHOR]

Abstract: Heat evolution of stress-induced structural disorder ΔH s(ε) of a Zr55Al10Ni5Cu30 bulk metallic glass (BMG) during compressive constant ram-velocity deformation in the glass transition region (T g =680K) was deduced from in situ measurements of temperature change ΔT(ε) of deforming samples, where ε is true strain. At transition from the linear to nonlinear viscoelasticity, i.e., a softening phenomenon, viscosity η(ε) does not change consistently with ΔT(ε) but with ΔH s(ε). Therefore, it is concluded that the stress-induced structural disorder triggered this softening phenomenon. The viscous frictional heating of the softened alloy brings about the increase in ΔT, which also influences ΔH s. Because ΔT is determined by relationship between the power of the frictional heating and heat convection to the sample-surroundings, ΔH s and η can be positively controlled with varying thermal conductivity D of the surrounding materials, especially after the transition period. [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]

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]

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: The Mg-3.5Zn-0.6Gd (at. %) alloy was prepared and homogenized at 673K for 8h, and then extruded at 523K with an extrusion ratio of 9:1. The microstructure and mechanical properties of the extruded alloy have been investigated. Icosahedral quasicrystalline phase (I-phase) existed in extruded Mg–Zn–Gd-based alloys in two morphologies: (1) micron-scale I-phase formed in the solidification, (2) nano-scale ellipsoid-shape I-phase particles precipitated in the extrusion process. A definite orientation relationship and good atomic match between I-phase and α-Mg matrix were directly observed by conventional and high-resolution transmission electron microscopy (HRTEM), which contribute to the high tensile strength of 308MPa and the large plasticity of 16.4%. [Copyright &y& Elsevier]

The present work was aimed to demonstrate the possibility of forming Fe66Cr10Nb5B19 metallic glass coatings by detonation spraying and analyze the coating formation process. A partially amorphous Fe66Cr10Nb5B19 powder with particles ranging from 45 µm to 74 µm in diameter was used to deposit coatings on stainless steel substrates. The deposition process was studied for different explosive charges (fractions of the barrel volume filled with an explosive mixture (C2H2 + 1.1O2)). As the explosive charge was increased from 35% to 55%, the content of the crystalline phase in the coatings, as determined from the X-ray diffraction patterns, decreased. Coatings formed at explosive charges of 55–70% contained as little as 1 wt.% of the crystalline phase. In these coatings, nanocrystals in a metallic glass matrix were only rarely found; their presence was confined to some inter-splat boundaries. The particle velocities and temperatures at the exit of the barrel were calculated using a previously developed model. The particle temperatures increased as the explosive charge was increased from 35% to 70%; the particle velocities passed through maxima. The coatings acquire an amorphous structure as the molten particles rapidly solidify on the substrate; cooling rates of the splats were estimated. The Fe66Cr10Nb5B19 metallic glass coatings obtained at explosive changes of 55–60% showed low porosity (0.5–2.5%), high hardness (715–1025 HV), and high bonding strength to the substrate (150 MPa). [ABSTRACT FROM AUTHOR]

We designed a new microstructure control method (liquid metal replacement method) that creates entirely new composites using the original microstructure as a template. This method selectively replaces a specific phase from a composite with another phase based on differences in atomic interactions. We applied this method to the dissimilar material joining of immiscible titanium and magnesium. After diffusion bonding one side of an interlayer consisting of α-Ti / α-Sc phases to Ti, we butted the opposite side with Mg and reheated. At this interface, selective interdiffusion of Mg and Sc results in the replacement of only the α-Sc phase by the α-Mg phase, forming a new α-Ti / α-Mg bicontinuous microstructure using the α-Ti / α-Sc monotectoid microstructure as a template. The Sc that diffused to the Mg side formed a reaction layer where the MgSc (B2) and (Mg, Sc) solid solution coexisted. These novel composite structures and reaction layers strengthened the joint area. As a result, we suppressed fracture at the joint interface, causing fracture at Mg and achieving a maximum joint strength of 116 MPa. [Display omitted] • We welded dissimilar titanium and magnesium through a scandium-containing interlayer. • The magnesium melts selectively replaced specific phases of the Ti/Sc microstructure. • A three-dimensional bicontinuous microstructure of immiscible Ti/Mg phases formed at the joint interface. • We studied the relationship between the interlayer composition and tensile strength. [ABSTRACT FROM AUTHOR]

Liquid metal dealloying is a promising technique for synthesizing non-noble porous materials by preventing oxidation in a metallic melt. This method considers the heats of mixing between precursor elements and a melt element to design miscible and immiscible elements for a precursor. In this study, Ni and Co were selected as the miscible elements in an Mg melt as constituents of (FeCo) 100− x Ni x precursor alloys to understand the complex mechanisms of their dissolution behavior. Dissolution of the second miscible element, Co, was governed by the composition of the Mg melt, because the characteristics of the melt changed in the presence of a high amount of dissolved Ni and its convection. The synthesized FeCo ligaments showed morphology variations depending on the dealloying temperature: the ligaments become more elongated along the dealloying direction at higher temperatures. A double-gyroid-like porous structure with a narrow liquid channel, produced from the (FeCo) 70 Ni 30 precursor, exhibited the highest specific surface area at all processing temperatures from 600 °C to 800 °C. This structure differed completely from that of the typical porous Fe 80 Cr 20 alloy produced under the same liquid metal dealloying conditions. Elongation resulted from time-dependent directional coarsening behavior that was affected by the composition of the Mg melt. Unlabelled Image • First demonstration of 3D interconnected porous FeCo materials produced by liquid metal dealloying • Ligament morphology depends on ordering and coarsening mechanisms at different temperatures. • Strong interaction between FeCo ligaments and the Mg melt affected coarsening behavior. • Double-gyroid-like structure showed the highest specific surface area. • Prerequisite conditions for dissolution of the second miscible element are identified. [ABSTRACT FROM AUTHOR]

Abstract Liquids metal dealloying is a new technology to create porous materials. In this study, a commercial Incoloy 825 nickel superalloy is dealloyed for 1 h at 3 different temperatures to elaborate a fully porous FeCr-based metal with 3 different porous microstructures. The resulting porous metals showed unimodal pore distribution, hierarchical structure or, contain large ligaments inclusions. The passivation ability of the porous material was conformed irrespective of the microstructure. This letter proves the possibility of fabricating low cost high specific surface materials for electrochemical applications. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

To obtain anisotropic nanoporous NiCr , some NiCr-Ag composites were prepared using a liquid metal dealloying method and were cold rolled before etching. While immersing (Ni 90 Cr 10 ) 60 Cu 40 precursors in a molten Ag bath, Cu atoms selectively migrate into the Ag bath. After cooling down to room temperature, the resulting microstructure is a bi-continuous structure of NiCr and A g (with Cu in solid solution). These ingots are strong enough to be cold rolled in one or two (perpendicular) directions with a thickness reduction of 70%. A final etching step removes the A g solid-state solution phase. The influence of cold rolling on the microstructure was investigated using X-ray tomography and on the mechanical properties using nanoindentation. We will show how introducing anisotropy into the microstructure and in the mechanical properties was successful while being able to preserve the porous state. [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]

Graphical abstract Highlights • Ti 25 Cu 75 alloy was as a source of Ti and Cu to synthesize TiC-Cu nanocomposites. • During milling, the alloy experienced crystallization and decomposition. • In sintered composites, there were Cu regions 0.5–1 µm in size free from TiC. • Ti-Cu intermetallics transformed into non-agglomerated TiC 10–20 nm in size. • Hardness of nanocomposites exceeded that of conventional TiC-Cu composites. Abstract In this work, Ti 25 Cu 75 melt-spun partially amorphous alloy was used as a source of Ti and Cu to synthesize in-situ TiC-Cu nanocomposites. The reaction between the alloy and carbon started during ball milling and continued during Spark Plasma Sintering. At the same time, during ball milling, the alloy experienced phase transformations: crystallization of the amorphous phase was followed by decomposition of TiCu 3. Copper crystallites formed during the alloy transformations were the reason for the presence of copper regions 0.5–1 µm in size free from TiC nanoparticles in the sintered composites. The Ti-Cu intermetallics transformed into non-agglomerated TiC 10–20 nm in size distributed in the copper matrix. The hardness of the synthesized TiC-Cu nanocomposites exceeded that of composites obtained by conventional sintering of ball-milled Ti-C-Cu powders. [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]

[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]

• A novel Fe-Ni-Co-Mn-Ti-Si MEA strengthened by heterogeneous microstructure was developed. • A superior combination of high-strength (YS ~ 930 MPa and UTS ~ 1075 MPa) and ductility (30%) has been achieved. • The deformation-induced martensitic transformation occurs during the straining of samples. • HDI and high plastic-incompatibility between the martensite and austenitic contributes to the high strength and ductility. In the work reported here, the mechanical properties of a newly developed Fe-Ni-Co-Mn-Ti-Si medium-entropy alloy with heterogeneous microstructure were investigated. High yield strength (~930 MPa), high ultimate tensile strength (~1100 MPa), and good ductility (~30%) were achieved using hetero-deformation-induced strengthening and high plastic-incompatibility between mechanically induced-martensite and the austenitic matrix. [ABSTRACT FROM AUTHOR]

• Substituting few percents of Cu in TiZrCuPd BMG improves its passive behavior. • Sn and Si elements play a beneficial role on the metallurgical quality of BMG. • Heterogeneity within solid solution and casting defects act as weakening sites. • Adding Sn and Si elements limit the susceptibility to pitting corrosion. In this work, the effect of substituting Cu with small amounts of Sn and Si on the passive behavior and pitting resistance of the bulk metallic glass Ti 40 Zr 10 Cu 36 Pd 14 was investigated. The Sn/Si substitution promoted homogenization of the solid solution and limited the presence of casting defects. In addition, unlike the heterogeneous passive film grown on TiZrCuPd, the passive films of the micro-alloyed materials were homogeneous, implying less sensitivity to film weakening and breakdown. Thus, alloying with small amounts of Sn and Si appears to be a viable approach to drastically improve the corrosion resistance of TiZrCuPd. [ABSTRACT FROM AUTHOR]