A method for measuring single-crystal elastic moduli using high-energy X-ray diffraction and a crystal-based finite element model

This paper presents a method – based on high-energy synchrotron X-ray diffraction data and a crystal-based finite element simulation formulation – for understanding grain scale deformation behavior within a polycrystalline aggregate. We illustrate this method by using it to determine the single-crystal elastic moduli of β21s, a body-centered cubic titanium alloy. We employed a polycrystalline sample. Using in situ loading and high-energy X-rays at the Advanced Photon Source beamline 1-ID-C, we measured components of the lattice strain tensor from four individual grains embedded within a polycrystalline specimen. We implemented an optimization routine that minimized the difference between the experiment and simulation lattice strains. Sensitivity coefficients needed in the optimization routine are generated numerically using the finite element model. The elastic moduli that we computed for the β21s are C₁₁ = 110 GPa, C₁₂ = 74 GPa and C₄₄ = 89 GPa. The resulting Zener anisotropic ratio is A = 5.     

Development of in situ NiAl–Al2O3 nanocomposite by reactive milling and spark plasma sintering

NiAl–10 vol.% Al₂O₃ in situ nanocomposite has been synthesized by reactive milling and subsequent spark plasma sintering. The synthesized nanocomposites have ～96% of theoretical density after sintering at 1000 °C for 5 min. Microstructural analysis of consolidated samples using TEM has revealed the presence of α-Al₂O₃ particles of 10–12 nm size in NiAl matrix of submicron grain size. Consolidated NiAl–10 vol.% Al₂O₃ nanocomposite has shown very high hardness of 772 HV_0.3 and compressive strength of 2456 MPa with ～14% plastic strain. The high hardness and compressive yield strength are attributed to the presence of nanocrystalline α-Al₂O₃ particles and the appreciable plastic strain is attributed to the submicron grains of NiAl.     

Titanium-supported Ce-, Zr-containing oxide coatings modified by platinum or nickel and copper oxides and their catalytic activity in CO oxidation

A combination of plasma electrolytic oxidation (PEO) and impregnation techniques followed by annealing in air has been used to obtain composites Pt/nZrO₂ + pTiO₂/Ti, Pt/nZrO₂ + pTiO₂ + zCeO_x/Ti, NiO + CuO/nZrO₂ + pTiO₂/Ti, NiO + CuO/nZrO₂ + pTiO₂ + zCeO_x/Ti with different zirconium and titanium contents and ZrO₂/TiO₂ phase ratio. The composites have been investigated by means of XRD, XPS and SEM/XSA methods. According to the XPS data, the platinum content on the coating surface is ~ 0.4 at.%, whereas the XSA measurements have shown that the nickel and copper contents in coatings attain 16 and 8 at.%, respectively, depending on the initial oxide coatings composition. Nickel and copper oxides form either extended islets or solid layers (“crusts”) on the coating surface. Both the composites promoted with platinum and those with the “crust” built from nickel and copper oxides are active in CO oxidation at the temperatures above 200 °C and 300 °C, respectively.     

Impact of He and Cr on defect accumulation in ion-irradiated ultrahigh-purity Fe(Cr) alloys

The effect of He on the primary damage induced by irradiation in ultrahigh-purity (UHP) Fe and Fe(Cr) alloys was investigated by transmission electron microscopy (TEM). Materials were irradiated at room temperature in situ by TEM in a microscope coupled to two ion accelerators, simultaneously providing 500 keV Fe⁺ and 10 keV He⁺ ions. Single Fe ion and dual Fe and He ion beam experiments were performed up to a dose of 1 dpa and to a He content of up to 1000 appm. Defects appear in the form of nanometric black dots with sizes between 1 and 5 nm. Defocused images reveal a dense population of sub-nanometric cavities after both single-beam and dual-beam irradiation. In Fe(Cr) alloys, the number densities of visible black dot defects still resolved in TEM are significantly higher after single than after dual-beam irradiation. In UHP Fe, conversely, the presence of He strongly increases the defect number density. The presence of He changes a a₀〈1 0 0〉 dominated defect population to a 1/2a₀〈1 1 1〉 dominated one in all materials, and the more so in UHP Fe. It appears that Cr increases the number of visible defects relative to UHP Fe. The dependence with increasing Cr content is weak, however, showing only a slight decrease in the number densities. The decrease in the density of visible a₀〈1 0 0〉 loops and increase in the visible 1/2a₀〈1 1 1〉 loops in all materials when He is present supports the idea that visible a₀〈1 0 0〉 loops are formed by the interaction between mobile 1/2a₀〈1 1 1〉 loops, as the latter would be immobilized by He already at sub-microscopic sizes. It is concluded that the primary loop population is dominated by 1/2a₀〈1 1 1〉 loops.     

Synthesis,morphology, microstructure and magnetic properties of hematite submicron particles

We report on hydrothermal synthesis, plate-like morphology, microstructure and magnetic properties of hematite (α-Fe₂O₃) plate-like particles. The sample is obtained immediately after the hydrothermal process without using any template and without further heat treatment. The so-obtained sample is characterized by X-ray powder diffraction (XRPD), energy-dispersive X-ray spectroscopy (EDX), field-emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and superconducting quantum interference device (SQUID) magnetometer. XRPD confirms the formation of a single-phase hematite sample whereas EDX reveals that iron and oxygen are the only components of the sample. SEM, FE-SEM, TEM and HRTEM show that the sample is composed of plate-like particles. The width of the particles is ～500 nm whereas thickness is ～100 nm (aspect ratio 5:1). The HRTEM images exhibit well defined lattice fringes of α-Fe₂O₃ particles that confirm their high crystallinity. Moreover, the HRTEM analysis indicates the plate-like particles preferring crystal growth along [0 1 2] direction. Magnetic measurements display significant hysteretic behavior at room temperature with coercivity H_C = 1140 Oe, remanent magnetization M_r = 0.125 emu/g and saturation magnetization M_S = 2.15 emu/g as well as the Morin transition at T_M ～ 250 K. The magnetic properties are discussed with respect to morphology and microstructure of the particles. The results and comparison with urchin-like, rods, spherical, hexagonal, star-like, dendrites, platelets, irregular, nanoplatelets, nanocolumns and nanospheres hematites reveal that the plate-like particles possess good magnetic properties. One may conjecture that the shape anisotropy plays an important role in the magnetic properties of the sample.     

Formation of bulk metallic glasses in Cu45Zr48−xAl7REx (RE = La,Ce, Nd,Gd and 0 ≤ x ≤ 5 at.%)

We report a series of bulk metallic glass-forming alloys of compositions (Cu₄₅Zr_48−xAl₇RE_x, RE = La, Ce, Nd, Gd and 0 ≤ x ≤ 5 at.%). By using a conventional copper mold sucking method, alloys with diameters ranging from 5 to 10 mm can be readily solidified into an amorphous structure without detectable crystallites. The best glass-forming ability is obtained for the alloys Cu₄₅Zr₄₆Al₇RE₂. Possible effects of RE addition on the glass-forming ability are discussed. In addition, the compositional effect on mechanical properties of Zr–Cu–Al–Gd alloys is presented.     

Structure of a new ternary compound with high magnesium content,so-called Gd13Ni9Mg78

The magnesium-rich composition Gd₁₃Ni₉Mg₇₈ was synthesized from its constituent elements in sealed tantalum tubes in an induction furnace. X-ray diffraction, electron probe microanalysis and dark-field transmission electron microscopy (TEM) images revealed a new compound with a composition ranging from Gd_10–15Ni_8–12Mg_72–78 and low crystallinity. In order to increase the crystallinity, different experimental conditions were investigated for numerous compounds with the initial composition Gd₁₃Ni₉Mg₇₈. In addition, several heat treatments (from 573 to 823 K) and cooling rates (from room temperature quenched down to 2 K h^?1) have been tested. The best crystallinity was obtained for the slower cooling rates ranging from 2 to 6 K h^?1. From the more crystallized compounds, the structure was partially deduced using TEM and an average cubic structure with lattice parameter a = 4.55 Å could be assumed. A modulation along both a¹ and b¹ axis with vectors of modulation q1 = 0.42a¹ and q2 = 0.42b¹ was observed. This compound, so-called Gd₁₃Ni₉Mg₇₈, absorbs around 3 wt.% of hydrogen at 603 K, 30 bars and a reasonable degree of reversibility is possible, because after the first hydrogenation, irreversible decomposition into MgH₂, GdH₂ and NiMg₂H₄ has been shown. The pathway of the reaction is described herein. The powder mixture after decomposition shows an interesting kinetics for magnesium without ball milling.     

Synthesis and characterization of the Mg-based amorphous/nano ZrO2 composite alloy

Mg-based composites are fabricated through mechanical alloying (MA) in the planetary mill, using amorphous Mg₆₅Cu_25−xY₁₀Ag_x (x=0, 5, 10) matrix alloy prepared by melt spun and 1–5 vol.% spherical nano-sized ZrO₂ particles. The melt spun amorphous matrix ribbons are ground into powders and mixed with the ZrO₂ nano particles in the planetary mill, after then formed by hot pressing in Ar atmosphere under different pressures at the temperature 5 K above the glass transition temperature (T_g). The microstructure characterizations of the resulting specimens are conducted by means of XRD, FEG-SEM, and TEM techniques. It is found that the nano-sized ZrO₂ dispersed Mg-based composite alloy powders can reach to a homogeneous size distribution (about 80 nm) after 50 h mechanical alloying. After hot pressing of these composite alloy powders under the pressure of 1100 MPa at 409 K, a 96% dense bulk specimen can be formed. Throughout the MA and hot pressing, the amorphous nature of the Mg₆₅Cu_25−xY₁₀Ag_x matrix is maintained. The hardness of the formed bulk Mg-based composites (with 5 vol% nano-sized ZrO₂ particles) can reach to 360 in H_v scale. In addition, the microstructure near the interface between the matrix and nano particles presents a well-bonded condition.     

Synthesis and hydrogen reduction of nano-sized copper tungstate powders produced by a hydrothermal method

The pure nano-sized copper tungstate (CuWO₄) powders were prepared by hydrothermal method and consequent annealing at 500 °C for 120 min. The thermogravimetric analysis was used to study dehydration processes, and the scanning electron microscopy (SEM) indicated that CuWO₄ particles were mostly spherical in the size range from 60 to 90 nm. Hydrogen reduction at 800 °C for 60 min converted the CuWO₄ to W–Cu composite powders. The hydrogen reduction results showed that nano-sized CuWO₄ particles calcining at 500 °C for 120 min indicated finer microstructure than the other calcination temperatures of 0 °C, 400 °C, 620 °C, 650 °C and 700 °C. W–Cu particles were observed finest and homogeneous in the size range from 90 to 150 nm by SEM images. Homogeneous distribution of W and Cu particles was clearly demonstrated by elemental mapping. Encapsulation of Cu phase by the W phase was observed by EDS and TEM. From FFT and HRTEM images, the orientation relationship of (01-1)_Cu ∥(01-1)_W and a semicoherent interface between W and Cu phases could be observed. A good correlation between the HRTEM image and the calculated lattice misfit (δ) was obtained.     

Oxidation behavior and phase transition of ZrB2–SiCw–ZrO2f ceramic

The oxidation behavior and phase transition of ZrB₂–SiC_w–ZrO_2f ceramic had been investigated by in situ high-temperature XRD, XPS, SEM, EDS and TEM measurements. The initial oxidation temperature of most ZrB₂ was 1000 °C and no significant oxidation of SiC was found up to 1200 °C. The oxidation products formed at lower temperatures would penetrate into the pores and flaws on the surface, which was beneficial to crack healing. In order to improve the oxidation resistance of this system, it should be focused on decreasing the oxygen diffusivity and the volume expansion caused by phase transition.     

Enhanced mechanical properties due to structural changes induced by devitrification in Fe–Co–B–Si–Nb bulk metallic glass

Fe₃₆Co₃₆B_19.2Si_4.8Nb₄ bulk glassy rods were synthesized by copper mould casting. The effects of annealing treatments on the microstructure, elastic and mechanical properties of this alloy are investigated. Annealing below the glass transition temperature induces the formation of atomic clusters with pseudo-tenfold symmetry with a close relationship to the Fe₂₃B₆ phase. Annealing at sufficiently high temperatures promotes the formation of stable Fe₂B and FeB phases and Fe(Co) solid solution. The as-cast alloy exhibits ultra-high hardness (H > 14 GPa), high reduced Young’s modulus (E_r > 200 GPa) and good wear resistance. These properties are further enhanced after thermal treatments (H > 18 GPa and E_r > 260 GPa are achieved in the fully crystallized sample). The mechanical hardening is accompanied with an increase of the elastic recovery and a decrease of the Poisson’s ratio. The different microstructural mechanisms responsible for these annealing-induced changes in mechanical and elastic properties are discussed.     

Structure and properties of 6061 + 26 mass% Si aluminum alloy produced via coupled rapid solidification and KOBO-extrusion of powder

Experiments on mechanical consolidation of rapidly solidified (RS) powder of 6061 + 26 mass% Si alloy were performed using the oscillating-die extrusion method. The RS powder was wrapped in thin-wall 6061-alloy cup 35 mm in diameter and vacuum-compressed by means of 100 ton press. Bars 8 mm in diameter were extruded with cross-section reduction of λ = 19 without any preheating of the charge. Tubes with a diameter/wall thickness of 14 mm/1 mm and cross-section reduction of λ = 33 were also manufactured with success. TEM/STEM observations revealed a very fine structure of as-extruded material and bimodal distribution of quasi-spherical silicon particles. Statistical analysis revealed a silicon fine fraction of 0.1–0.7 μm and a coarse fraction 2.1–2.5 μm in diameter. Examination by means of TEM did not reveal any significant changes in the morphology of the silicon particles, even when a high extrusion ratio and the material annealing after deformation were used. Hot compression tests on as-extruded rods (λ = 19) and preliminary annealed samples were performed at a constant true strain rate of 5 × 10^?3 s^?1 within the temperature range of 293–823 K. High strength of the material and relatively high ductility of samples deformed by compression up to ?_t ? 0.4 were observed. The maximum flow stress value for as-extruded material was reduced with deformation temperature from ～390 to ～3.5 MPa for 293 and 823 K, respectively. Annealing of the samples at 773 K/30 min was found to reduce the maximum flow stress by 30–40%. Tensile strengths of similar as-cast alloys and materials manufactured by means of other powder metallurgy methods were shown for the purpose of comparison.     

Estimation of magneto-crystalline uniaxial anisotropy constant of β-FeOOH by Mössbauer spectroscopy

The magneto-crystalline uniaxial anisotropy constant, K_u, of β-FeOOH was estimated by analyzing temperature dependence of Mössbauer absorption spectra taking into account the thermal relaxation of the internal magnetic fields. It was deduced to be 2.1 × 10³ J/m³, using a typical volume (9 × 10^?24 m³) of synthesized β-FeOOH particles observed by TEM. The value, K_u of β-FeOOH is in the same order but twice as large as that of α-FeOOH, 1 × 10³ J/m³.     

Density dependence of the compressive properties of porous copper over a wide density range

The compressive properties of porous copper with relative densities, ρ/ρ_s, of 0.22–0.96 were investigated. In the low relative density range (ρ/ρ_s < 0.5–0.6), porous copper showed a density exponent n of 2.3, where n represents the relative density dependence of yield strength. In this range, the bending and buckling of cell walls and the formation of macroscopic deformation bands were observed. However, porous copper with a higher relative density (0.5–0.6 < ρ/ρ_s < 0.9–1) had an n value of ∼1, where the dominant deformation mode of cell walls was yielding, and no clear deformation band was observed. Also, in the highest relative density range (ρ/ρ_s very close to 1), the compressive properties degraded markedly with decreasing density, indicating that stress concentration around the minimal pores occurred in this density range.     

Ti50Cu23Ni20Sn7 bulk metallic glasses prepared by mechanical alloying and spark-plasma sintering

A powder metallurgy technology was developed to prepare Ti₅₀Cu₂₃Ni₂₀Sn₇ bulk metallic glasses (BMGs). Firstly, amorphous powder was prepared by mechanical alloying (MA) method successfully after being milled for 30 h. Phase transformation of the as-milled powder was characterized by X-ray diffraction (XRD). Morphology of the as-milled amorphous powder was observed by scanning electron microscopy (SEM). Onset temperature of glass transformation and onset temperature of crystallization (T_x and T_g) of the as-milled amorphous powder were evaluated by differential scanning calorimeter (DSC). Secondly, the as-milled amorphous powder was then consolidated by spark-plasma sintering (SPS) method into a specimen with the shape of cylindrical stick, with a diameter and height of about 20 and 10 mm, respectively. The SPS experiment was conducted under a pressure of 500 MPa at a heating rate of 40 K/min, sintering and holding for 1 min at the temperature of 763 K. It was confirmed that the as-milled powder is of fully amorphous however the consolidated specimen shows to be an amorphous matrix with partial crystallization. Compressing strength, Young's modulus, micro-hardness, friction and density of the consolidated specimen are about 975 MPa, 121 GPa, 13 GPa, 0.12 and 6599 kg/m³, respectively. Fractograph of the specimen appears to be shear fracture and very few defects can be seen from the picture of SEM.     

Corrosion of ultra-high-purity Mg in 3.5% NaCl solution saturated with Mg(OH)2

Corrosion was evaluated for ultra-high-purity magnesium (Mg) immersed in 3.5% NaCl solution saturated with Mg(OH)₂. The intrinsic corrosion rate measured with weight loss, P_W = 0.25 ± 0.07 mm y⁻¹, was slightly smaller than that for high-purity Mg. Some specimens had somewhat higher corrosion rates attributed to localised corrosion. The average corrosion rate measured from hydrogen evolution, P_AH, was lower than that measured with weight loss, P_W, attributed to dissolution of some hydrogen in the Mg specimen. The amount of dissolution under electrochemical control was a small amount of the total dissolution. A new hydride dissolution mechanism is suggested.     

Crystal structure of τ5–TiNi2−xAl5 (x = 0.48) and isotypic {Zr,Hf}Ni2−xAl5−y

The crystal structure of the compound in the Al-rich region of the Ti–Ni–Al system, τ₅–TiNi_2?xAl₅, x = 0.48, has been derived from X-ray powder and single crystal, neutron powder and electron diffraction (space group I4/mmm, a = 0.3984(2) nm, c = 1.4073(3) nm, R_F2 = 0.0133). Titanium atoms were unambiguously located from neutron powder data. τ₅ is isotypic with the crystal structure of ZrNi₂Al₅. Detailed transmission electron microscopy (TEM) in several crystallographic directions confirmed the lattice parameters and crystal symmetry. Although occupancy of Ni in the 4e site revealed a defect (occ. = 0.76), no significant homogeneity region was observed for this phase at 1020°C. Rietveld analyses of X-ray powder diffraction data for the Zr- and Hf-homologues confirmed for both compounds isotypism and revealed defects in the Ni sites and to a lesser extent also in the Al sites: ZrNi_2?xAl_5?y, x = 0.4, y = 0.4 and HfNi_2?xAl_5?y, x = 0.5, y = 0.2. The crystallographic relations among the structure types of Cu, TiAl₃, ZrNi₂Al₅ and Zr(Ni,Ga)₇ have been defined in terms of a Bärnighausen scheme.     

Enhanced microwave absorption properties in polyaniline and nano-ferrite composite in X-band

Highly conducting polyaniline (PANI) nanocomposite with Mn_0.2Ni_0.4Zn_0.4Fe₂O₄ ferrite was prepared by mechanical blending. The present work reports the EMI shielding characteristics of the ferrite-Pani nanocomposite with different thickness. The saturation magnetization (Ms) for pure MnNiZn ferrite (52 emu/g) and composite (41 emu/g) was measured by VSM at room temperature. The crystalline size of MnNiZn ferrite was found in the range of 25–30 nm as analyzed by TEM and XRD. The complex permittivity, permeability and shielding effectiveness of the composite for different thicknesses were measured in the 8–12 GHz (X-band) frequency range. The composite of 2.5 mm thickness has shown high shielding effectiveness (49.2 dB) due to absorption (SE_A). The high value of SE_A suggests that this composite can be used as a promising absorbing material for X-band frequency range.     

Epitaxial Ti2AlN(0 0 0 1) thin film deposition by dual-target reactive magnetron sputtering

Ultrahigh-vacuum dual-target reactive magnetron sputtering, in a mixed Ar/N₂ discharge was used to deposit epitaxial single-crystal MAX phase Ti₂AlN(0 0 0 1) thin films, without seed layers, onto Al₂O₃(0 0 0 1) substrates kept at 1050 °C. By varying the N₂ partial pressure a narrow process window was identified for the growth of single-crystal Ti₂AlN. The film microstructure was characterized by a combination of X-ray diffraction, spherical aberration (C_s) corrected transmission electron microscopy (TEM), high-resolution image simulation and high-resolution scanning TEM. Nitrogen-depleted deposition conditions resulted in the concurrent formation of N-free Ti–Al intermetallics at the film/substrate interface and a steady-state growth of Ti₂AlN together with N-free intermetallic phases. At higher N₂ partial pressures the growth assumes a columnar epitaxial nature. 1 Å resolution of the lattice enabling location of all elements in the Ti₂AlN unit cell is demonstrated.     

Microstructural characteristics and microwave dielectric properties of Ba[Mg1/3(Nbx/4Ta(4−x)/4)2/3]O3 ceramics

Sintering behaviors and microstructural characteristics in solid solutions of Ba[Mg_1/3(Nb_x/4Ta_(4−x)/4)_2/3]O₃ (BMN_xT_4−x, x = 0, 1, 2, 3 and 4) were investigated by X-ray diffraction, SEM and TEM. Microwave dielectric properties, such as the relative permittivity (ɛ_r), quality factor (Q) value and temperature coefficient of resonator frequency (τ_f), were also measured. The excellent microwave dielectric property of Ba(Mg_1/3Ta_2/3)O₃ (BMT) sample imply the necessity to sinter at higher temperature (1650 °C) and to use longer soaking times (9 h), but not for Ba(Mg_1/3Ta_2/3)O₃ (BMN). The 1:2 B-site ordering was maintained at all Nb substitution contents and the 1:2 B-site ordering existed in the grains with antiphase domain boundaries (APBs). The Ba[Mg_1/3(Nb_1/4Ta_3/4)_2/3]O₃ specimen exhibited excellent microwave dielectric properties, ɛ_r = 25.534, Qf = 140 666 GHz, and τ_f = 4.8 (ppm/°C). The excellent microwave dielectric property is due to the improvement of sintering property by appropriate Nb atoms substitution in the BMT matrix and the maintaining of 1:2 ordering in the BMN_xT_4−x series.