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The phase stability, microstructural evolution, and mechanical properties of Al0.6CoCrFeNi high-entropy alloy (HEA) subjected to different thermo-mechanical treatments were systematically investigated in the present study. The face center... more
The phase stability, microstructural evolution, and mechanical properties of Al0.6CoCrFeNi high-entropy alloy (HEA) subjected to different thermo-mechanical treatments were systematically investigated in the present study. The face center cubic (FCC) matrix, B2, and minor Body Center Cubic (BCC) phases were observed in the as-cast state. The morphology of the B2 precipitates evolved from needle-like to droplet-shaped when annealed at 900 °C, 1000 °C, and 1100 °C. The resulting yield stress of this FCC/B2 duplex-phase HEA after annealing heat treatments was successfully analyzed based on the contributions from solid solution strengthening, precipitate strengthening, grain boundary hardening, and dislocation hardening.
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... Wei ZHAO, Peter K. LIAW and David C. JOY* 323 Dougherty Engineering Building, The University of Tennessee, 15 12 Middle Drive, Knoxville, TN 37996 *232 ... quite evenly in both the fiber region (Pixel 20 to 100) and the matrix region... more
... Wei ZHAO, Peter K. LIAW and David C. JOY* 323 Dougherty Engineering Building, The University of Tennessee, 15 12 Middle Drive, Knoxville, TN 37996 *232 ... quite evenly in both the fiber region (Pixel 20 to 100) and the matrix region (Pixel 1 to 20, and after Pixel loo), with the ...
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Amorphous and solid-solution phases are both with high entropy; the former is mainly with topological disorder while the later is mainly with chemical disorder. The amorphous phase forms at lower temperatures usually below the eutectic... more
Amorphous and solid-solution phases are both with high entropy; the former is mainly with topological disorder while the later is mainly with chemical disorder. The amorphous phase forms at lower temperatures usually below the eutectic temperature, while the solid-solution phase forms at higher temperatures. Mechanical-alloying results have verified that amorphous and solid-solution phases are the two terminal phases by enough long time of milling of the component elements. The phase formation regions, e.g., amorphous, intermetallic compound, and solid-solution, were summarized from the literature and experimental data, with the parameter of the atomic-size differences, δ, and the parameter of Ω. Recently, the definition of the high-entropy alloys (HEAs) was also extended to four components and one of the elements may exceed 35%. Wires with diameters at micro- and nanoscale were prepared by the melt-extracted and thermal-plastic forming method. The dynamic mechanical properties of the wires were evaluated.
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Microstructures in nanocrystalline Ni-Fe alloys during cold rolling are quantitatively investigated by synchrotron high-energy X-ray diffraction. It is found that rolling leads to an obvious reduction in the densities of both dislocations... more
Microstructures in nanocrystalline Ni-Fe alloys during cold rolling are quantitatively investigated by synchrotron high-energy X-ray diffraction. It is found that rolling leads to an obvious reduction in the densities of both dislocations and twins and an increase in crystallite size. A huge dislocation flux flows through the grains during rolling, even though only a small fraction remains in the specimen
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The recent interest in the bulk nanocrystalline (NC) metals and alloys has focused mainly on improving their ductility [1], [2] and [3]. By contrast, the fatigue behavior of these NC metals has not been explored extensively. One of the... more
The recent interest in the bulk nanocrystalline (NC) metals and alloys has focused mainly on improving their ductility [1], [2] and [3]. By contrast, the fatigue behavior of these NC metals has not been explored extensively. One of the reasons lies in the fact that the sample size of ...
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Research Interests: Materials Science, Neutron Diffraction, Medicine, Nanocrystalline Material, Mesoscale Meteorology, and 14 morePhysical sciences, Dislocation, Dislocations, Grain size, Nickel, Grain Boundary, X ray diffraction, Plastic deformation, Grain Size and Shape, Textures, Experimental Data, Coarse Grained Soil, Deformation Mechanism, and Mechanical Property
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Research Interests: Materials Engineering, Mechanical Engineering, Materials Science, Thermodynamics, Heat Transfer, and 12 moreThermography, Nondestructive Evaluation, Nondestructive testing, Crack propagation, Thermal Imaging, Phase Transformation, High Speed, Infrared, Very High Cycle Fatigue, Fatigue Testing, High Sensitivity, and imaging system
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Internal-strain profiles in friction-stir processed aluminum-alloy plates were investigated using neutron diffraction. Three different specimens were prepared with a purpose of separating the effects of frictional heating and severe... more
Internal-strain profiles in friction-stir processed aluminum-alloy plates were investigated using neutron diffraction. Three different specimens were prepared with a purpose of separating the effects of frictional heating and severe plastic deformation on the internal-strain distribution: (Case 1) a plate processed with both stirring pin and tool shoulder, (Case 2) a plate processed only with the tool shoulder, and (Case 3) a plate processed only with the pin. The comparison between Cases 1 and 2 shows distinctly different strain profiles revealing deconvoluted effects of the different sources (i.e., heat, deformation, or the combination) on the internal strains generated during the friction-stir processing.
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The plastic behavior of an annealed HASTELLOY C-22HS alloy, a face-centered cubic (FCC), nickel-based superalloy, was examined by in-situ neutron-diffraction measurements at room temperature. Both monotonic-tension and low-cycle-fatigue... more
The plastic behavior of an annealed HASTELLOY C-22HS alloy, a face-centered cubic (FCC), nickel-based superalloy, was examined by in-situ neutron-diffraction measurements at room temperature. Both monotonic-tension and low-cycle-fatigue experiments were conducted. Monotonic-tension straining and cyclic-loading deformation were studied as a function of stress. The plastic behavior during deformation is discussed in light of the relationship between the stress and dislocation-density evolution. The calculated dislocation-density evolution within the alloy reflects the strain hardening and cyclic hardening/softening. Experimentally determined lattice strains are compared to verify the hardening mechanism at selected stress levels for tension and cyclic loadings. Combined with calculations of the dislocation densities, the neutron-diffraction experiments provide direct information about the strain and cyclic hardening of the alloy.
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This paper presents a bilinear log model, for predicting temperature-dependent ultimate strength of high-entropy alloys (HEAs) based on 21 HEA compositions. We consider the break temperature, T break , introduced in the model, an... more
This paper presents a bilinear log model, for predicting temperature-dependent ultimate strength of high-entropy alloys (HEAs) based on 21 HEA compositions. We consider the break temperature, T break , introduced in the model, an important parameter for design of materials with attractive high-temperature properties, one warranting inclusion in alloy specifications. For reliable operation, the operating temperature of alloys may need to stay below T break. We introduce a technique of global optimization, one enabling concurrent optimization of model parameters over low-temperature and high-temperature regimes. Furthermore, we suggest a general framework for joint optimization of alloy properties, capable of accounting for physics-based dependencies, and show how a special case can be formulated to address the identification of HEAs offering attractive ultimate strength. We advocate for the selection of an optimization technique suitable for the problem at hand and the data available, and for properly accounting for the underlying sources of variations.
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The full information on the changes in many crystallographic aspects, including the structural and microstructural characterizations, during the phase transformation is essential for understanding the phase transition and “memory”... more
The full information on the changes in many crystallographic aspects, including the structural and microstructural characterizations, during the phase transformation is essential for understanding the phase transition and “memory” behavior in the ferromagnetic shape-memory alloys. In the present article, the defects-related microstructural features connected to the premartensitic and martensitic transition of a Ni2MnGa single crystal under a uniaxial pressure of 50 MPa applied along the [110] crystallographic direction were studied by the in-situ high-energy X-ray diffuse-scattering experiments. The analysis of the characteristics of diffuse-scattering patterns around different sharp Bragg spots suggests that the influences of some defect clusters on the pressure-induced phase-transition sequences of Ni2MnGa are significant. Our experiments show that an intermediate phase is produced during the premartensitic transition in the Ni2MnGa single crystal, which is favorable for the nucleation of a martensitic phase. The compression stress along the [110] direction of the Heusler phase can promote the premartensitic and martensitic transition of the Ni2MnGa single crystal.
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ABSTRACT Using an infrared camera, the temperature evolution of as-cast and relaxed bulk metallic glasses during compression was measured. Substantial variations in the temperatures of both glasses during plastic deformation were... more
ABSTRACT Using an infrared camera, the temperature evolution of as-cast and relaxed bulk metallic glasses during compression was measured. Substantial variations in the temperatures of both glasses during plastic deformation were observed, which are conjectured to result at least partially from shear-banding phenomena. The relaxed glass has a larger temperature rise than the as-cast glass, which can be attributed to a reduction in the free volume. The larger temperature increase in the relaxed glass may be responsible for the observed work softening. The relaxed glass also has a higher maximum temperature than the as-cast, which can be attributed to a stronger strain-rate dependence of the temperature rise rate, and a shorter dissipation time scale for the heat due to conduction. The experimental data follow the well-known model behavior, and suggest the possibility of a statistical correlation between the fluctuations of strain rates and the rates of the temperature variation.
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Understanding how to predict the fatigue lifetimes of bulk-metallic glass (BMG) materials is crucially important for their selection as structural alloys. In our paper, the nature of likely fatigue mechanisms for BMGs is revealed. Fatigue... more
Understanding how to predict the fatigue lifetimes of bulk-metallic glass (BMG) materials is crucially important for their selection as structural alloys. In our paper, the nature of likely fatigue mechanisms for BMGs is revealed. Fatigue cracks, arising from machining/polishing damage, were experimentally observed to initiate from shear bands near defects. At the crack tip, a plastic-zone creation is observed through the formation of many shear bands, and the fatigue crack is found to propagate along these shear bands. The size of the plastic zone can be characterized by fracture-mechanics quantities, and each fatigue cycle is seen to produce a fine striation instead of a single coarse one. We propose a shear-band mechanism to explain the characteristics of the observed fatigue cracking. Numerical computations, based on linear-elastic-fracture mechanics, yield reasonably good agreement with experiments. Our findings are significant to predict the fatigue lifetimes of these materials.
Research Interests: Engineering, Materials Science, Applied Physics, Numerical Analysis, Fatigue, and 11 moreMetallic Glass, Shear bands, Mathematical Sciences, Physical sciences, Bending, Fracture Mechanic, BMG (Bulk Metallic glasses), Plastic deformation, Numerical computation, Bulk Metallic Glass, and Linear elastic fracture mechanics
Simultaneously enhancing strength and ductility of metals and alloys has been a tremendous challenge. Here, we investigate a CoCuFeNiPd high-entropy alloy (HEA), using a combination of Monte Carlo method, molecular dynamic simulation, and... more
Simultaneously enhancing strength and ductility of metals and alloys has been a tremendous challenge. Here, we investigate a CoCuFeNiPd high-entropy alloy (HEA), using a combination of Monte Carlo method, molecular dynamic simulation, and density-functional theory calculation. Our results show that this HEA is energetically favorable to undergo short-range ordering (SRO), and the SRO leads to a pseudo-composite microstructure, which surprisingly enhances both the ultimate strength and ductility. The SRO-induced composite microstructure consists of three categories of clusters: face-center-cubic-preferred (FCCP) clusters, indifferent clusters, and body-center-cubic-preferred (BCCP) clusters, with the indifferent clusters playing the role of the matrix, the FCCP clusters serving as hard fillers to enhance the strength, while the BCCP clusters acting as soft fillers to increase the ductility. Our work highlights the importance of SRO in influencing the mechanical properties of HEAs and...
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For this study, the effects of thermal annealing and compressive strain rate on the complexity of the serration behavior in a Zr-based bulk metallic glass (BMG) was investigated. Here, as-cast and thermally-annealed (300 °C, 1 week)... more
For this study, the effects of thermal annealing and compressive strain rate on the complexity of the serration behavior in a Zr-based bulk metallic glass (BMG) was investigated. Here, as-cast and thermally-annealed (300 °C, 1 week) Zr52.5Cu17.9Ni14.6Al10Ti5 BMG underwent room-temperature compression tests in the unconstrained condition at strain rates of 2 × 10−5 s−1 and 2 × 10−4 s−1. The complexity of the serrated flow was determined, using the refined composite multiscale entropy technique. Nanoindentation testing and X-ray diffraction characterization were performed to assess the changes in the microstructure and mechanical properties of the BMG that occurred during annealing. The results indicated that the BMG did not crystallize during annealing in the prescribed heating condition. Nanoindentation tests revealed that annealing led to a significant increase in the depth-dependent nanoindentation hardness and Young’s modulus, which were attributed to the structural relaxation in...
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Unalloyed nickel aluminide has important applications but lacks ductility at room temperature. In this study, iron-added nickel aluminide alloys exhibit plasticity enhancement. The nickel aluminide alloys are prepared with different iron... more
Unalloyed nickel aluminide has important applications but lacks ductility at room temperature. In this study, iron-added nickel aluminide alloys exhibit plasticity enhancement. The nickel aluminide alloys are prepared with different iron contents (0, 0.25, and 1 at%) to study their plasticity. The indentation-induced deformed areas are mapped by the synchrotron X-ray diffraction to compare their plastic zones. A complimentary tight binding calculation and generalized embedded atom method demonstrate how the Fe-addition enhances the plasticity of the iron-added nickel aluminide alloys.
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This review summarizes the state of high-entropy alloys and their combinatorial approaches, mainly considering their magnetic applications. Several earlier studies on high-entropy alloy properties, such as magnetic, wear, and corrosion... more
This review summarizes the state of high-entropy alloys and their combinatorial approaches, mainly considering their magnetic applications. Several earlier studies on high-entropy alloy properties, such as magnetic, wear, and corrosion behavior; different forms, such as thin films, nanowires, thermal spray coatings; specific treatments, such as plasma spraying and inclusion effects; and unique applications, such as welding, are summarized. High-entropy alloy systems that were reported for both their mechanical and magnetic properties are compared through the combination of their Young’s modulus, yield strength, remanent induction, and coercive force. Several potential applications requiring both mechanical and magnetic properties are reported.
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In-situ dendrite/metallic glass matrix composites (MGMCs) with a composition of Ti₄₆Zr₂₀V₁₂Cu₅Be₁₇ exhibit ultimate tensile strength of 1510 MPa and fracture strain of about 7.6%. A tensile deformation model is established, based on the... more
In-situ dendrite/metallic glass matrix composites (MGMCs) with a composition of Ti₄₆Zr₂₀V₁₂Cu₅Be₁₇ exhibit ultimate tensile strength of 1510 MPa and fracture strain of about 7.6%. A tensile deformation model is established, based on the five-stage classification: (1) elastic-elastic, (2) elastic-plastic, (3) plastic-plastic (yield platform), (4) plastic-plastic (work hardening), and (5) plastic-plastic (softening) stages, analogous to the tensile behavior of common carbon steels. The constitutive relations strongly elucidate the tensile deformation mechanism. In parallel, the simulation results by a finite-element method (FEM) are in good agreement with the experimental findings and theoretical calculations. The present study gives a mathematical model to clarify the work-hardening behavior of dendrites and softening of the amorphous matrix. Furthermore, the model can be employed to simulate the tensile behavior of in-situ dendrite/MGMCs.
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After an overload was imposed during a constant amplitude fatigue experiment, a retardation period was observed. The deformation in the vicinity of a crack tip was studied using neutron and x-ray microbeam-diffraction techniques, which... more
After an overload was imposed during a constant amplitude fatigue experiment, a retardation period was observed. The deformation in the vicinity of a crack tip was studied using neutron and x-ray microbeam-diffraction techniques, which provide millimeter and submicrometer spatial resolutions, respectively. From the neutron-diffraction measurements, compressive lattice strains and higher dislocation densities at the macroscale were observed in front of the crack tip, which indicates a plasticity induced crack-closure phenomenon. Furthermore, Laue patterns obtained from the microbeam diffraction at different locations near the crack tip show alternating regions with high and low dislocation densities at the mesoscale.