Influence of Space Charge During the Oxidation of Metal Surfaces

In this work we present a model for the surface oxide film growth considering the influence of space charge. The space charge field E_sp is assumed proportional to the charge of moving metal ions and electrons in the oxide layer. The surface charge field E_ox decreases as the Cabrera and Motts’ oxide thickness X grows to its limit X₁ (E_ox = V_M/X). E_ox remains constant for further growth of the oxide film (E_ox = V_M/X₁). The obtained equation for the growing rate of the oxide film covers two stages. The first stage is characterized by a negligible space charge and is described by the typical inverse logarithmic law. During transition from thin to thick film, the oxidation growth rate is described by a direct logarithmic law which is confirmed by many experiments. At the end of this stage, the drift of metal ions is replaced by their diffusion that leads to parabolic law.     

Movement of Multiple Markers in Cu/Zn Multiple Phase Diffusion Couples and Its Numerical Analysis

Movement of multiple markers (M-Ms) embedded in the Cu end member of a Cu/Zn multiple phases diffusion couple (M-couple) has been experimentally investigated at 623 K and the alignment of the M-Ms after diffusion anneal was reproduced by the numerical analysis that the authors have previously reported. Two intermediate phases, γ and ?, were found in the Cu/Zn M-couple. The M-Ms bent toward Zn side at Cu/γ phase interface and show almost a linear line in the γ phase. They again bent at γ/? interface toward Zn side. The Kirkendall marker position, X _k, locates in the ? phase layer. From this result, ratio, R = D _Zn/D _Cu, of the intrinsic diffusion coefficients with respect to the mole fixed frame of reference was determined to be about 46 at X _k. On the assumption of a constant value of R = 46 in the ? phase and appropriate constant values of R = 10-1000 in the γ phase, alignments of M-Ms after diffusion anneal were numerically reproduced. By fitting the alignment of M-Ms obtained numerically on the experimental result, the value R in γ phase is estimated to be very large value of 500.     

Preparation and Thermoelectric Properties of Sn-Based Type VIII Single-Crystalline Clathrate Via a-Sn Flux Method

In this study, type VIII Ba₈Ga₁₆Sn₃₀ single-crystal clathrates with different stoichiometric ratios were prepared using the a-Sn self-flux method. The structures of the samples were also investigated. Results indicate that n-/p-type single-crystal clathrates can be obtained by adjusting the initial content of Ga. Samples were determined to be n-type when the initial Ga content was X = 12, 13, and 14; and p-type when X = 16 and 18. The samples exhibited high melting points and large lattice parameters, as well as increasing Ga content. The electrical conductivities of the samples were lower than those prepared using the Sn self-flux method because of the low carrier concentration. The elemental composition of the sample was near the theoretical value when the Ga content was X = 14 and 16, which also yielded the highest Seebeck values of ?523 μV/K and 331 V/K, respectively. Finally, the sample with X = 14 and 18 exhibited the highest ZT values of 0.82 and 0.46, respectively, at a temperature of 480 K in n-/p-type.     

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.     

Phase Equilibria in the Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript>–InSb System

The phase diagram of the (Sb₂Te₃)_100?x –InSb _x system was determined based on x-ray diffraction (XRD) analysis, differential thermal analysis (DTA), and microhardness and density measurements. An intermediate compound with composition Sb₂Te₃·2InSb was formed as a result of syntectic reaction, melting incongruently at 553 °C. This compound has tetragonal lattice with unit cell parameters of a = 4.3937 Å, b = 4.2035 Å, c = 3.5433 Å, α = 93.354°, and β = γ = 90°. Sb₂Te₃·(2 + δ)InSb (?1 ≤ δ ≤ +1) and (Sb₂Te₃)_100?x (InSb) _x (90 ≤ x ≤ 100) solid solutions exist in the investigated system, based on the intermediate compound Sb₂Te₃·2InSb and on InSb, respectively. Also, two invariant equilibria exist in the system, with eutectic point coordinates at compositions of x = 60 and x ≈ 85 mol% InSb and eutectic temperatures of T _E = 541 and T _E ≈ 501 °C, respectively.     

Phase Equilibria of the Ternary Al-Cu-Zn Alloys on Al-Zn Rich Side

Phase equilibria of the Al-Cu-Zn system on Al-Zn rich side was experimentally determined with 16 alloys annealed at 360 °C. The annealed alloys were examined by means of x-ray diffraction, electron probe microanalysis and differential scanning calorimetry. Five single-phase regions and seven two-phase regions as well as three three-phase regions, i.e. α-(Al)?+?θ-Al₂Cu?+?τ′-Al₄Cu₃Zn, α-(Al)?+?τ′-Al₄Cu₃Zn?+?ε-CuZn₄ and α-(Al)?+?ε-CuZn₄?+?(Zn), were determined. The partial isothermal section of the Al-Cu-Zn system on Al-Zn rich side at 360 °C was constructed based on the obtained experimental data in this work. It was observed that the solid solution phase α-(Al) would easily decompose into ε-CuZn₄, (Zn) and α′-(Al) at the ambient temperature in the early stages. The ternary phase τ′-Al₄Cu₃Zn would form and ε-CuZn₄ would disappear gradually along with the extension of aging time.     

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.     

Magnetoresistive properties of Ni-doped La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> manganites

La_0.7Sr_0.3Mn_1?x Ni _x O₃ (x = 0, 0.025, 0.050 and 0.075) ceramics were prepared by the conventional solid-state reaction method. The partial substitution of Mn by Ni²⁺ leads to a decrease in cell volume as well as a structural transition from the rhombohedral to the orthorhombic structure. Ni²⁺ doping increases the electrical resistivity, decreases the semiconductor–metal transition temperature (T _ms) and relatively enhances the room temperature magnetoresistance (MR), especially in x = 0.025 and around T _ms. With respect to conduction mechanism, the small polaron hopping (SPH) and the variable range hopping (VRH) models were used to examine conduction in the semiconducting region.     

Correlation Between the Pitting Potential Evolution and $$\varvec\sigma$$ Phase Precipitation Kinetics in the 2205 Duplex Stainless Steel

The aim of this work is to correlate the pitting potential (E_pit) evolution with the kinetics of σ phase precipitation in the 2205 duplex stainless steel aged at 850 °C after solution treatment at 1150 °C. The potentiodynamic polarization curves indicate a reduction of the pitting corrosion resistance with the aging time, which is revealed by a decrease in the E_pit values from 0.65 to 0.40 V_SCE. Thus, E_pit values are used to determine the kinetics parameters of the σ phase precipitation. The experimental transformed fraction agrees well with the one calculated by using the modified Kolmogorov–Johnson–Mehl–Avrami equation with an impingement parameter c?=?0.6.     

Cohesive Properties of Cu-X and Ni-X (In,Sn) Intermetallics: Ab Initio Systematics,Correlations and “Universality” Features

This paper reports an analysis of the systematics of cohesive properties and equation-of-state parameters for a large number of stable, metastable and hypothetical binary Me_aX_b type phases formed by Me = Cu, Ni with X = In, Sn. To this aim, an ab initio database previously developed by the authors using spin polarized density-functional-theory calculations, using the VASP code, is adopted. The work involves the volume (V ₀), Wigner–Seitz radius, bulk modulus (B ₀) and cohesive energy (E _coh) of the phases. At the outset of the paper it is shown that these properties can be studied as functions of the average group number (AGN), i.e., the weighted average of the number of valence electrons involved in the VASP calculations. Moreover, the cohesive energy density (CED), defined as E _coh/V ₀, is shown to correlate very well with the AGN variable and with B ₀. These striking regularities are given two complementary interpretations. First, a general microscopic picture of the variations of cohesion is developed by studying the evolution of the contributions of the d- and p-electrons to their electronic density of states. In this way the effects of the hybridization of d- and p-electrons, and the filling up of bonding and anti-bonding states is highlighted. Next, a thermodynamic analysis based on the classical approach developed by Rose, Ferrante, Smith and collaborators is performed. It is concluded that the correlation involving CED and B ₀ is a manifestation of a significant degree of “universality” in the variation of the cohesive properties with the Wigner–Seitz radius of these compounds.     

Experimental Determination of the Phase Equilibria of the La-Zn-Si System at 600 °C

The isothermal section at 600 °C of the La-Zn-Si system was established by using equilibrated alloys and the diffusion couple technique. Microstructural observation and phase identification were performed using optical microscopy, scanning electron microscopy with energy dispersive x-ray spectroscopy and a wave dispersive x-ray spectrometer, and x-ray powder diffraction. Seven ternary compounds were identified in this ternary system, and temporally designated as τ ₁, τ ₂, τ ₃, τ ₄, τ ₅, τ ₆ and τ ₇. Two previously reported ternary compounds, viz. τ ₁ and τ ₂, were found to exist at 600 °C. EDS analysis revealed that the τ ₁ phase contained Si from 2.4 to 6.1 at.% and La from 22.3 to 23.3 at.%. The compositional region of the τ ₂ single-phase ranged from 28.3 to 40.7 at.% for Si and from 31.5 to 33.1 at.% for La. Two new ternary phases, τ ₅ and τ ₆, were identified. The τ ₅ phase with the CeNiSi₂-type was determined to have a composition range of 36.9-39.2 at.% Si for about 24 at.% La. The τ ₆ phase with the ThCr₂Si₂-type was found to have a composition range of 18.9-19.7 at.% La and 27.4-30.6 at.% Si. The crystal structures of τ ₃, τ ₄, and τ ₇ were not determined. The solubility of Si in LaZn₁₃, LaZn₁₁, La₂Zn₁₇, La₃Zn₂₂, and LaZn₅ was negligible, and that of Si in LaZn₄, LaZn₂ and Zn in LaSi₂, La₃Si₂ was determined as 5.1, 2.3, 16.2 and 3.8 at.%, respectively.     

Investigation of the Corrosion Inhibition of CTAB and SDS on Carbon Steel Using an Experimental Design Strategy

The corrosion inhibition performance of sodium dodecyl sulfate (SDS) and cetyltrimethyl ammonium bromide (CTAB) on carbon steel was investigated in sodium chloride solutions. Using an experimental design strategy pH, chloride concentration, SDS/CTAB concentrations, and temperature were optimized by conducting only 30 experiments. The optimum value of each factor was obtained from the designed matrix of the experiments based on the lowest log I _corr value calculated for each experimental condition. The 3D surface plots of the electrochemical response (log I _corr) against each factor were constructed. The optimum conditions in which the lowest log I _corr can be achieved were found as follows: pH 12, [Cl^?] ≈ 1 M, [SDS] ≈ 200 ppm, [CTAB] ≈ 20 ppm, and T ≈ 10 °C.     

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.     

Isothermal Section of Er-Ag-Sn System at 873 K

The isothermal section of the Er-Ag-Sn system at 873 K was constructed with the use of scanning electron microscopy, energy-dispersive x-ray microanalysis and x-ray powder diffraction. Two ternary compounds were confirmed at this temperature: ErAgSn (LiGaGe structure type, P6₃mc, Z = 2, a = 4.6595(2) Å, c = 7.2872(3) Å) and non-stoichiometric phase ErAg_1?xSn_2+x (Cu₃Au structure type, Pm-3m, Z = 1). For the last one homogeneity range was established (0.08 < x < 0.24) and lattice parameters were determined (a = 4.5007(4), 4.5040(2), 4.5107(1), 4.5412(1) Å for the compositions Er_25.4Ag_23.4Sn_51.2, Er_25.7Ag_23.0Sn_51.3, Er_25.7Ag_21.7Sn_52.6, Er_25.2Ag_18.6Sn_56.2 (at.%) respectively). Melting point of the phase Er_25.7Ag_21.7Sn_52.6 (at.%) was determined to be 1199 K by differential thermal analysis.     

Microstructures,Martensitic Transformation,and Mechanical Behavior of Rapidly Solidified Ti-Ni-Hf and Ti-Ni-Si Shape Memory Alloys

In this work, the microstructure and mechanical properties of rapidly solidified Ti_50?x/2Ni_50?x/2Hf _x (x = 0, 2, 4, 6, 8, 10, and 12 at.%) and Ti_50?y/2Ni_50?y/2Si _y (y = 1, 2, 3, 5, 7, and 10 at.%) shape memory alloys (SMAs) were investigated. The sequence of the phase formation and transformations in dependence on the chemical composition is established. Rapidly solidified Ti-Ni-Hf or Ti-Ni-Si SMAs are found to show relatively high yield strength and large ductility for specific Hf or Si concentrations, which is due to the gradual disappearance of the phase transformation from austenite to twinned martensite and the predominance of the phase transformation from twinned martensite to detwinned martensite during deformation as well as to the refinement of dendrites and the precipitation of brittle intermetallic compounds.     

Prediction of Martensite Start Temperature for Lightweight Fe-Mn-Al-C Steels

A tailor-made thermodynamic database of the Fe-Mn-Al-C system was developed using the CALPHAD approach. The database enables predicting phase equilibria and thereby assessing the resulting microstructures of Fe-Mn-Al-C alloys. Available information on the martensite start (M_s) temperature was reviewed. By employing the M_s property model in the Thermo-Calc software together with the new thermodynamic database and experimental M_s temperatures, a set of model parameters for the Fe-Mn-Al-C system in the M_s model was optimised. Employing the newly evaluated parameters, the calculated M_s temperatures of the alloys in the Fe-Mn-Al-C system were compared with the available measured M_s temperatures. Predictions of M_s temperatures were performed for the alloys, Fe-10, 15 and 20 wt.% Mn-xAl-yC. The predictability of the M_s model can be further validated when new experimental M_s temperatures of the Fe-Mn-Al-C system are available.     

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.     

Isothermal Section of the Al-Mn-Dy System at 500 °C

Phase relationships in the Al-Mn-Dy ternary system at 500 °C have been investigated by X-ray diffraction, scanning electron microscopy with energy dispersive spectroscopy, and electron probe microanalysis. From the experimental results it was concluded that the isothermal section consists of 16 single-phase regions, 26 two-phase regions and 12 three-phase regions. Two extensive solid solutions, (Al _x Mn_1?x )₁₂Dy and (Al_1?x Mn _x )₂Dy, were observed. The solid solution (Al _x Mn_1?x )₁₂Dy forms by Al replacing Mn in Mn₁₂Dy, while the continuous solid solution (Al_1?x Mn _x )₂Dy forms by Mn and Al mutually substituting in Al₂Dy and Mn₂Dy, respectively. The maximum solid solubility of Al in Mn₁₂Dy is 79.3 at.%.     

Effect of Strain Rate on Deformation Behavior of AlCoCrFeNi High-Entropy Alloy by Nanoindentation

In this study, nanoindentation tests with continuous stiffness measurement technique were measured to investigate the deformation behavior of a high-entropy alloy AlCoCrFeNi under different indentation strain rates at room temperature. Results suggest that the creep behavior exhibits remarkable strain rate dependence. In-situ scanning images showed a conspicuous pileup around the indents, indicating that an extremely localized plastic deformation occurred during the nanoindentation. Under different strain rates, elastic modulus basically remains unchanged, while the hardness decreases with increasing indentation depth due to the indentation size effect. Furthermore, the modulus and hardness of AlCoCrFeNi HEAs are greater than that of the Al _x CoCrFeNi (x = 0.3,0.5) at the strain rate of 0.2 s^?1 due to its higher negative enthalpy of mixing related to the atomic binding force, and the solid solution strengthening induced by the lattice distortion, respectively.     

Composition dependences of thermodynamical properties associated with Pb-free ternary,quaternary, and quinary solder systems

In the present study, Chou’s General Solution Model (GSM) has been used to predict the enthalpy and partial enthalpies of mixing of the liquid Ag–In–Sn ternary, Ag–In–Sn–Zn quaternary, and Ag–Au–In–Sn–Zn quinary systems. These are of technical importance to optimize lead-free solder alloys, in selected cross-sections: x_In/x_Sn = 0.5/0.5 (ternary), Au–In_0.1–Sn_0.8–Zn_0.1, Ag–In_0.1–Sn_0.8–Zn_0.1 (quaternary), and t = x_Au/x_In = 1, x_In = x_Sn = x_Zn (quinary) at 1173, 773, and 773 K, respectively. Moreover, the activity of In content in the ternary alloy system Ag–In–Sn has been calculated and its result is compared with that determined from the experiment, while the activities of Ag contents associated with the alloys mentioned above have been calculated. The other traditional models such as of Colinet, Kohler, Muggianu, Toop, and Hillert are also included in calculations. Comparing those calculated from the proposed GSM with those determined from experimental measurements, it is seen that this model becomes considerably realistic in computerization for estimating thermodynamic properties in multicomponent systems.