Microstructural,mechanical, and electrical characterization of directionally solidified Al–Cu–Mg eutectic alloy

The composition of an Al–Cu–Mg ternary eutectic alloy was chosen to be Al–30 wt% Cu–6 wt % Mg to have the Al₂Cu and Al₂CuMg solid phases within an aluminum matrix (α-Al) after its solidification from the melt. The alloy Al–30 wt % Cu–6 wt % Mg was directionally solidified at a constant temperature gradient (G = 8.55 K/mm) with different growth rates V, from 9.43 to 173.3 μm/s, by using a Bridgman-type furnace. The lamellar eutectic spacings (λ_E) were measured from transverse sections of the samples. The functional dependencies of lamellar spacings λ_E (\({\lambda _{A{l_2}CuMg}}\) and \({\lambda _{A{l_2}Cu}}\) in μm), microhardness H _V (in kg/mm²), tensile strength σ_T (in MPa), and electrical resistivity ρ (in Ω m) on the growth rate V (in μm/s) were obtained as \({\lambda _{A{l_2}CuMg}} = 3.05{V^{ - 0.31}}\), \({\lambda _{A{l_2}Cu}} = 6.35{V^{ - 0.35}}\), \({H_V} = 308.3{\left( V \right)^{ - 0.33}}\); σ_T= 408.6(V)^0.14, and ρ = 28.82 × 10^–8(V)^0.11, respectively for the Al–Cu–Mg eutectic alloy. The bulk growth rates were determined as \(\lambda _{A{l_2}CuMg}^2V = 93.2\) and \(\lambda _{A{l_2}Cu}^2V = 195.76\) by using the measured values of \({\lambda _{A{l_2}CuMg}}\), \({\lambda _{A{l_2}Cu}}\) and V. A comparison of present results was also made with the previous similar experimental results.     

Temperature-Dependent Flow Behavior and Microstructural Evolution During Compression of As-Cast Mg-7.7Al-0.4Zn

The microstructure and mechanical properties improve substantially by hot working. This aspect in as-cast Mg-7.7Al-0.4Zn (AZ80) alloy is investigated by compression tests over temperature range of 30-439°C and at strain rates of 5 × 10^?2, 10^?2, 5 × 10^?4 and 10^?4 s^?1. The stress exponent (n) and activation energy (Q) were evaluated and analyzed for high-temperature deformation along with the microstructures. Upon deformation to a true strain of 0.80, which corresponds to the pseudo-steady-state condition, n and Q were found to be 5 and 151 kJ/mol, respectively. This suggests the dislocation climb-controlled mechanism for deformation. Prior to attaining the pseudo-steady-state condition, the stress-strain curves of AZ80 Mg alloy exhibit flow hardening followed by flow softening depending on the test temperature and strain rate. The microstructures obtained upon deformation revealed dissolution of Mg₁₇Al₁₂ particles with concurrent grain growth of α-matrix. The parameters like strain rate sensitivity and activation energy were analyzed for describing the microstructure evolution also as a function of strain rate and temperature. This exhibited similar trend as seen for deformation per se. Thus, the mechanisms for deformation and microstructure evolution are suggested to be interdependent.     

Integrated constitutive model for flow behavior of pure Titanium considering interstitial solute concentration

The aim of this work is to develop a constitutive model that can predict the flow behavior of pure Ti with different interstitial concentrations and grain sizes. To build a database required for identifying material constants, three different grades of Ti were subjected to tensile tests at temperatures of 223, 300, 473, 673 or 773 K and at a fixed strain rate of 10^?3 s^?1. In the modeling procedure, the mechanical threshold stress model was further modified to capture both the hardening effects attributed to the changes in equivalent oxygen concentration (O _eq ) and the softening effect caused by deformation heating at high strain rates. The developed model can reasonably predict the flow behavior of pure Ti having different O _eq (0.14–0.32 wt%), and grain size (14.5–90 μm) over a temperature range of 135 to 673 K, and a strain rate range of 2×10^?4 to 1400 s^?1.     

The Effect of Synthesis Conditions on the Phase Composition and Structure of EuBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>6 + δ</Subscript> Samples

The composition and the structure of ceramic EuBa₂Cu₃O_{6 + δ} (Eu-123) oxide samples annealed in steps with varying processing conditions (in air or oxygen and argon atmosphere at a temperature of 940–960°С for 1–70 h with or without homogenization) were studied by the X-ray phase and chemical analysis, electron diffraction pattern analysis, elemental analysis, and high-resolution transmission electron microscopy. Regardless of the processing conditions, Eu-123 nanostructured oxide with a tetragonal or orthorhombic structure and domains 1–20 nm in size was obtained as a result of annealing. Nanostructuring of the samples, which was revealed by high-resolution electron microscopy, is attributed to their chemical nature: the presence of identical structural elements in members of the homologous Eu _n Ba _m Cu_{m + n}O _y series of oxides allows them to intergrow coherently and create an illusion of a single crystal. Just like any other member of the Eu _n Ba _m Cu_{m + n}O _y series, oxide Eu-123 is disproportionate depending on the annealing conditions to form other members of this series located on either side of the dominant oxide. Temperature T_c of the superconducting transition of each member of the series depends on the average oxidation state of copper \(\overline {Cu} \). At \(\overline {Cu} \) < 2, all members of the series have a tetragonal structure and do not exhibit superconducting properties. At \(\overline {Cu} \) = 2.28, five members of the Eu _n Ba _m Cu_{m + n}O _y series with matrices (Ba : Cu) 5 : 8, 3 : 5, 2 : 3, 5 : 7, and 3 : 4 exhibit superconducting properties with T_c = 82–90 K.     

Development of Texture in Interstitial-Free Steel Processed by Equal-Channel Angular Pressing

Ti + Nb-stabilised interstitial-free steel is deformed by equal-channel angular pressing (ECAP) adopting a route B_C up to an equivalent strain of 24. Upon ECAP the grain size decreases to ultrafine level and it becomes strongly textured. At ε_vm = 0.6-6, components of both {110} fiber, \( J_{\uptheta } \), \( \bar{J}_{\uptheta } \) and of 〈111〉 fiber, D _1θ, D _2θ with common components of E _θ, \( \bar{E}_{\uptheta } \) are existing but after ε_vm ≥9, only 〈111〉 fiber components are observed. At large strain, ε_vm = 9-24, 〈111〉 fiber texture is recorded with monoclinic symmetry. At ε_vm = 0.6, coarse grains get split into deformation bands. Fragmentation of bands (at ε_vm = 3) suppress \( \bar{J}_{\uptheta } , \) \( J_{\uptheta } \) components. At ε_vm = 6, formation of lamellar structures increases intensity of mainly D _1θ, D _2θ. At ε_vm = 9, oriented ribbon grains result in strong D _1θ, D _2θ components with 〈111〉 fiber. At ε_vm = 15-24, conversion of ribbon grains to near-equiaxed shaped grains maintains 〈111〉 fiber texture with enhanced intensity of D _1θ and D _2θ components.     

Constitutive modeling and understanding of the hot compressive deformation of Mg–9.5Zn–2.0Y magnesium alloy with reduced number of strain-dependent constitutive parameters

The hot compressive flow behavior of the cast Mg–9.5Zn–2.0Y alloy as a function of strain was analyzed, and the degree of dependence of the parameters (A: material constant, n ₂: stress exponent, Q _c: activation energy for plastic flow and α: stress multiplier) of the constitutive equation (\(\dot \varepsilon = A{\left[ {\sinh \left( {\alpha \sigma } \right)} \right]^{{n_2}}}\exp \left( {\frac{{ - {Q_c}}}{{RT}}} \right)\)) upon the strain was examined in a systematic manner. This is to explore the possibility of representing the hot compressive deformation behavior of metallic alloys in a simple way by using a reduced number of strain-dependent constitutive parameters. The analysis results for several different cases can be interpreted as follows: (1) Q _c can be treated as being strain-independent, which is physically sensible; (2) while only the microstructure changes as a function of strain at low flow stresses, as the flow stress increases, the power-law creep deformation and power-law breakdown mechanisms change; (3) the regime where only A is strain dependent expanded to higher strain rates and lower temperatures as the strain increased, suggesting that the number of the strain-dependent parameters decreases as the initial microstructure is refined by dynamic recrystallization, and the microstructure approaches a steady state.     

Influence of Zinc on Coarsening of δ-Ni<Subscript>2</Subscript>Si Particles,Aging Behavior and Hardness in a Cu-Ni-Si Alloy

In the present paper, the aging precipitation and coarsening of disk-like δ-Ni₂Si particles in Cu and Cu-10Zn alloys aged at 450 °C have been investigated by hardness, electric resistivity measurement and transmission electron microscopy observation. The coarsening dynamics of the average diameter of the δ-Ni₂Si particles coincides with the t ^1/3 time law for both alloys. The coarsening of the diminution of supersaturation related to aging time t coincides with the t ^?1/3 time rule. Adding Zn to the Cu-Ni-Si alloy increases the growth and coarsening rate of the particles mainly because of the increased diffusivity D of the δ-Ni₂Si particles in the matrix. The value of D of the δ-Ni₂Si particles in the Cu-xZn (x = 0, 10 wt.%) matrix and the Cu/δ-Ni₂Si interfacial energy γ are independently calculated by using the Lifshitz–Slyozov–Wagner theory which was extended to include disk-like particles by Boyd and Nicholson. The values of D and γ increase from 0.77 × 10^?19 to 2.21 × 10^?19 m²/s and 0.19 to 0.63 J/m², respectively, when Zn is added to the Cu-Ni-Si alloy. These calculations and the analysis show that the properties of Cu-Ni-Si-Zn alloy can significantly be enhanced by reducing the aging temperature.     

Study on the Hot Workability of SiCp/Al Composites Based on a Critical Strain Map

We used the isothermal compression test (conducted in a Gleeble-3500 system) to study the hot deformation behaviors of SiCp/Al composites over a wide range of temperatures (623-773 K) and strain rates (0.001-10 s^?1). A 3D hot-processing map was constructed based on the Malas stability criteria and experimental data. An artificial neural network model of four hot work quality characteristic parameters (strain rate sensitivity m, its derivative m′, temperature sensitivity s, and its derivative s′) were established. A new hot-processing map, known as a hot-processing critical strain map, has been proposed based on the smallest strain prior to instability. Two optimized processing regions at 623-660 K, 0.05-0.075 s^?1 and 720-773 K, 0.04-0.18 s^?1 were determined based on this map.     

Preparation and high-frequency soft magnetic property of FeCo-based thin films

A series of FeCo-based thin films were prepared by magnetron sputtering without applying an induced magnetic field.The microstructure,electrical properties,magnetic properties and thermal stability of FeCo,FeCoSiN monolayer thin film and[FeCoSiN/SiN_x]_n multilayer thin film were investigated systematically.When FeCo thin film was doped with Si and N,the resistivity and soft magnetic properties of the obtained FeCoSiN thin film can be improved effectively.The coercivity(H_c),resistivity(ρ) and ferromagnetic resonance frequency(f_r) can be further optimized for the[FeCoSiN/SiN_x]_n multilayer thin film.When the thickness of FeCoSiN layer and SiN_x layer is maintained at 7 and 2 nm,the H_c,p and f_r for[FeCoSiN/SiN_x]_n multilayer thin film are 225 A·m~(-1)392 μΩ·cm~(-1) and 4.29 GHz,respectively.In addition,the low coercivity of easy axis(H_(ce) ≈ 506 A·m~(-1)) of[FeCoSiN/SiN_x]_n multilayer thin film can be maintained after annealing at 300 ℃ in air for 2 h.     

Analysis of Plastic Flow Instability During Superplastic Deformation of the Zn-Al Eutectoid Alloy Modified with 2 wt.% Cu

The aim of this work is to analyze the plastic flow instability in Zn-21Al-2Cu alloy deformed under 10^?3 s^?1 and 513 K, which are optimum conditions for inducing superplastic behavior in this alloy. An evaluation using the Hart and Wilkinson–Caceres criteria showed that the limited stability of plastic flow observed in this alloy is related to low values of the strain-rate sensitivity index (m) and the strain-hardening coefficient (γ), combined with the tendency of these parameters to decrease depending on true strain (ε). The reduction in m and γ values could be associated with the early onset of plastic instability and with microstructural changes observed as function of the strain. Grain growth induced by deformation seems to be important during the first stage of deformation of this alloy. However, when ε > 0.4 this growth is accompanied by other microstructural rearrangements. These results suggest that in this alloy, a grain boundary sliding mechanism acts to allow a steady superplastic flow only for ε < 0.4. For ε values between 0.4 and 0.7, observed occurrences of microstructural changes and severe neck formation lead to the supposition that there is a transition in the deformation mechanism. These changes are more evident when ε > 0.7 as another mechanism is thought to take over.     

High Pressure Oxidation of Metals: Tantalum in Oxygen

The temperature and pressure dependence of the reaction of tantalum in oxygen were investigated from 500° to 1000°C at pressures from 10 mm Hg to 600 psi total oxygen pressure. Tantalum was found to oxidize linearly under the above conditions. Three distinct regions of temperature dependence were found with different energies of activation. From 500° to 600°C the rate of oxidation of tantalum was found to be essentially independent of the oxygen pressure at the pressure investigated. The oxidation rate increases rapidly with an increase in pressure from 600° to 800°C. The dependence of the oxidation rate on the bulk concentration may be expressed by V = k′θ, where k′ is the specific rate constant and \(\theta=k_1C_{\text{O}_{2}}/(1\;+\;k_1C_{\text{O}_{2}})\), where k₁is the equilibrium constant for the adsorption of oxygen on tantalum.     

Hot Deformation Mechanisms of an As-Extruded TiAl Alloy with Large Amount of Remnant Lamellae

The hot deformation mechanisms of an as-extruded Ti-44Al-5V-1Cr alloy with a large amount of remnant lamellae were investigated by hot compression tests at temperatures of 900-1250 °C and strain rates of 0.001-1 s^?1. The hot processing map of the as-extruded Ti-44Al-5V-1Cr alloy was developed on the basis of dynamic materials modeling and the Prasad criteria. There were four different domains in the hot processing map, according to the efficiency of power dissipation, η. The flow soft and hot deformation mechanisms for different domains were illustrated in the context of microstructural evolution during the process of deformation. As a result, the dynamic recrystallization and superplastic deformation occurred at 1125-1150 °C near 0.001 s^?1, and this region is suitable for superplastic forming. The α phase dynamic recrystallization and dynamic recovery occurred at 1250 °C and 0.1 s^?1. The existence of small amount of the γ and β phases effectively inhibited the growth of α grains.     

Electrical Transport Properties of Single-Crystalline β-Zn<Subscript>4</Subscript>Sb<Subscript>3</Subscript> Prepared Through the Zn-Sn Mixed-Flux Method

β-Zn₄Sb₃ is a promising p-type thermoelectric material for utilization in moderate temperatures. This study prepares a group of single-crystalline β-Zn₄Sb₃ samples using the Zn-Sn mixed-flux method based on the stoichiometric ratios of Zn_4+x Sb₃Sn _y . The effect of Zn-to-Sn proportion in the flux on the structure and electrical transport properties is investigated. All samples are strip-shaped single crystals of different sizes. The actual Zn content of the present samples is improved (>3.9) compared with that of the samples prepared through the Sn flux method. Larger lattice parameters are also obtained. The carrier concentration of all the samples is in the order of over 10¹⁹ cm^?3. With increasing Sn rate in the flux, this carrier concentration decreases, whereas mobility is significantly enhanced. The electrical conductivity and Seebeck coefficients of all the samples exhibit a behavior that of a degenerate semiconductor transport. Electrical conductivity initially increases and then decreases as the Sn ratio in the flux increases. The electrical conductivity of the x:y = 5:1 sample reaches 6.45 × 10⁴ S m^?1 at 300 K. Benefitting from the electrical conductivity and Seebeck coefficient, the flux proportion of the x:y = 7:1 sample finally achieves the highest power factor value of 1.4 × 10^?3 W m^?1 K^?2 at 598 K.     

Microwave Power Absorption in Materials for Ferrous Metallurgy

The characteristics of microwave power absorption in materials for ferrous metallurgy, including iron oxides (Fe₂O₃, Fe₃O₄ and Fe₀.₉₂₅O) and bitumite, were explored by evaluating their dielectric loss (Q _E) and/or magnetic loss (Q _H) distributions in the 0.05-m-thick slabs of the corresponding materials exposed to 1.2-kW and 2.45-GHz microwave radiation at temperatures below 1100°C. It is revealed that the dielectric loss contributes primarily to the power absorption in Fe₂O₃, Fe_0.925O and the bitumite at all of the examined temperatures. Their Q _E values at room temperature and slab surface are 9.1311 × 10³ W m^?3, 23.7025 × 10³ W m^?3, and 49.5999 × 10³ W m^?3, respectively, showing that the materials have the following heating rate initially under microwave irradiation: bitumite > Fe_0.925O > Fe₂O₃. Compared with the other materials, Fe₃O₄ has much stronger power absorption, primarily originated from its magnetic loss (e.g., Q _H = 1.0615 × 10⁶ W m^?3, Q _H/Q _E = 2.4185 at 24°C and slab surface), below its Curie point, above which the magnetic susceptibility approaches to zero, thereby causing a very small Q _H value at even the surface (Q _H = 1.0416 × 10⁵ W m^?3 at 880°C). It is also demonstrated that inhomogeneous power distributions occur in all the slabs and become more pronounced with increasing temperature mainly due to rapid increase in permittivity. Characterizing power absorption in the oxides and the coal is expected to offer a strategic guide for improving use of microwave energy in ferrous metallurgy.     

Phase transformations during deformation of Fe-Ni and Fe-Mn alloys produced by mechanical alloying

Compositions of Fe_{(100 ? x)}Mn _x (x = 10 and 12 at. %) and Fe_{(100 ? y)}Ni _y (y = 18 and 20 at. %) were produced by combined mechanical alloying of pure-metal powders and annealed in the austenitic field. After annealing and cooling to room temperature, the alloys had a single-phase austenitic structure. During deformation, the γ phase partially transforms into the α ₂ phase (and/or ? phase in Fe-Mn alloys). The phase composition of the alloys after deformation depends on the amount of alloying elements and the predeformation annealing regime. The amount of martensite in the structure of a bulk alloy obtained by powder compacting grows proportionally to the degree of deformation of the sample.     

The Effect of Thermo-Mechanical Treatment on Structure of Ultrahigh Carbon PM Steel

The effects of thermo-mechanical treatment on selected properties related to the structure of Fe-0.85Mo-0.65i-1.4C powder metallurgy (PM) steel are reported. Three kinds of initial microstructure of specimens, i.e., pearlite + ferrite + cementite, martensite + retained austenite and α + spheroidized cementite were examined. Processing was carried out on a plastometer-dilatometer Bähr machine by compression cylindrical specimens at 775 °C at a strain rate of 0.001 s^?1. X-ray diffraction was carried out with symmetrical Bragg-Brentano and grazing incident angle methods on a D8-Advance diffractometer with filtered radiation of cobalt CoK _α . The following features were determined: texture, density of dislocations, density of vacancies, lattice parameter of Fe _α and mean size of crystallites. Significant differences in structure were observed, especially in quenched specimen, as a result of the thermo-mechanical treatment. Regardless of initial state of the specimens, the determined properties were on a similar level. Crystallite size was in the range 97-106 nm, crystallite texture (I{200}/I{110}) × 10 = 1.15-1.62 and density of vacancies I{110}/I{220} = 7.06-7.52.     

The Microstructural Evolution and Special Flow Behavior of Ti-5Al-2Sn-2Zr-4Mo-4Cr During Isothermal Compression at a Low Strain Rate

The microstructural evolution and special flow behavior of Ti-5Al-2Sn-2Zr-4Mo-4Cr during isothermal compression at a strain rate of 0.0001 s^?1 were investigated. The dislocation climbs in elongated α grains resulted in the formation of low-angle boundaries that transform into high-angle boundaries with greater deformation, and the elongated α grains subsequently separated into homogenous globular α grains with the penetration of the β phase. The simultaneous occurrence of discontinuous dynamic recrystallization and continuous dynamic recrystallization in the primary β grains resulted in a trimode grain distribution. The β grains surrounded by dislocations presented an equilateral-hexagonal morphology, which suggests that grain boundary sliding through dislocation climbs was the main deformation mechanism. The true stress–strain curves for 1073 and 1113 K abnormally intersect at a strain of ~0.35, related to the α → β phase transformation and distinct growth of the β grain size.     

Determination of Johnson–Cook Plasticity Model Parameters for Inconel718

In order to simulate foreign object damage (FOD) phenomenon in aircraft high-pressure compressor blades made of a nickel-based super-alloy, Johnson–Cook (J–C) plasticity model was used. For prediction of material’s plastic behavior at temperature of 400 °C (working temperature of the blades) in the range of strain rates associated with the FOD phenomenon (in order of 10⁶ s^?1), material parameters of A, B, C, n and m for the J–C plasticity model had to be determined experimentally. Parameters of A, B and n with values of 1108, 699 MPa and 0.5189, respectively, were obtained from quasi-static tensile tests. Moreover, m was determined to be 1.2861, also through quasi-static tensile tests with a strain rate of 1 s^?1 at three temperatures of 475, 550 and 625 °C. However, in order to determine C, firstly a steel ball was impacted on the surface of a flat specimen made of a precipitation-hardening alloy, and then, the impact site was 3D scanned to obtain the induced crater profile. Finally, the impact test (ballistic) was simulated using Abaqus, and a C value of 0.0085 was determined by comparing the actual crater profile with the one obtained from the simulation through a trial-and-error approach.     

Creep correlations of metals at elevated temperatures

Creep data for pure metals at temperatures above those at which rapid recovery occurs (above about 0.45 the melting temperature) are correctable by means of the equations ? = f (te^?ΔH/RT, σ) and σ = f (?&#x0307 _s e^ΔH/RT). These correlations were applied successfully to data for aluminum, iron, nickel, copper, zinc, platinum, gold, and lead as well as for simple alloys. For a given metal, ΔH is a constant about equal to the activation energy for self-diffusion.     

Experimental Investigation of the Binary Mn-Sb Phase Diagram

The binary manganese-antimony (Mn-Sb) phase diagram was reinvestigated in the whole composition range using powder-XRD, DTA and SEM-EDX. The phase boundaries and melting temperatures of the ferromagnetic phases MnSb and Mn₂Sb were modified by taking into account the new experimental data. Most of the reaction temperatures could be verified within a range of ±10 °C. Nevertheless, a few temperatures had to be revised, such as the eutectic reaction L → β-Mn + Mn ₂ Sb at 893 °C and the eutectoid reaction β-Mn → α-Mn + Mn ₂ Sb at 718 °C. The previously reported peritectic melting behavior of MnSb could be confirmed. The variation of the lattice parameters of the NiAs-(B8 ₁ ) type MnSb phase with composition was determined. A revised version of the of the Mn-Sb phase diagram is presented.