3D打印激光制备多孔镍合金组织和力学性能研究

采用3D打印激光熔化技术制备了多孔镍基合金,并对其显微组织构成和压缩力学性能进行了分析。研究结果表明,采用3D打印激光熔化技术制备的多孔镍合金,孔隙率为14.68%~18.97%、抗压强度为461~535 MPa,其微观组织主要呈现γ-Ni枝晶,压缩断口为撕裂式枝晶断裂。     

Temperature and velocity dependence of mechanical properties of the alloy Ni3Al. III

The temperatures and velocity dependence of the yield point and flow stress of the inter-metallic compound Ni₃Al was studied. It was established that, within the range of temperatures where the anomalous temperature dependence of flow stress is observed, an anomalous velocity dependence of these stresses also occurs. The increase of the yield point and flow stress of the alloy Ni₃Al with the increase of temperature is under the full control of thermally activated mechanisms of hardening. Three stages in the increase of resistance to deformation under increasing temperature were disclosed. It is assumed that two of these are associated with the deposition of atomic defects on sliding dislocations.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 11, pp. 107–113, November, 1971.     

Factors affecting the microstructure and mechanical properties of Ti-Al3Ti core-shell-structured particle-reinforced Al matrix composites

This work studied the effects of matrix powder and sintering temperature on the microstructure and mechanical properties of in situ formed Ti–Al₃Ti core–shell-structured particle-reinforced pure Al-based composites. It has been shown that both factors have significant effects on the morphology of the reinforcements and densification behaviour of the composites. Due to the strong interfacial bonding and the limitation of the crack propagation in the intermetallic shell during deformation by soft Al matrix and Ti core, the composite fabricated using fine spherical-shaped Al powder and sintered at 570 °C for 5 h has the optimal combination of the overall mechanical properties. The study provides a direction for the optimum combination of high strength and ductility of the composites by adjusting the fabrication parameters.     

Microstructure and oxidation behaviour of SiC fibre-reinforced Si3N4-AlN-Al2O3-Y2O3 matrix composites

A series of SiC fibre-reinforced Si₃N₄-AlN-Al₂O₃-Y₂O₃ matrix composites with different matrix compositions are fabricated by slurry infiltration followed by hot pressing at 1600°C for 30 min. The diffusion of yttrium and aluminium into fibres is apparent during the high temperature processing. All the as-processed composites show fracture with fibre pull-out. After heat treatment in air at 1000°C for 60 min, composites with minimal Y₂O₃ and Al₂O₃ in the matrix composition demonstrate the fracture behaviour with most extensive fibre pull-out. Composites with the highest aluminium and yttrium oxide content form an yttrium–aluminium–garnet phase and an aluminosilicate glassy phase. The latter phase provides an oxygen diffusion path, resulting in the removal of the carbon-rich interphase by oxidation. This results in catastrophic fracture without fibre pull-out after heat treatment of the composite in air.     

Microstructure and properties of Pb(Mg1/3Nb2/3)O3–Portland cement composites

Lead magnesium niobate, Pb(Mg_1/3Nb_2/3)O₃ (PMN), ceramics particles was mixed with Portland Cement (PC) using a water to cement ratio of 0.50 and PMN content at 40% and 60% by weight to produce 0–3 Pb(Mg_1/3Nb_2/3)O₃–Portland cement (PMN–PC) composites. Microstructure and hydration of the composites were investigated. Calcium silicate hydrate gel can be seen surrounding the PMN particles. Dielectric constant of the composites was found to increase with PMN content. Successful poling of the composites was achieved. Interestingly, SEM micrographs of the PMN40 composite clearly showed calcium silicate hydrate gel (an essential hydration product of Portland cement) surrounding the PMN particles. In PMN60 composite, the gel can also still be seen but of less quantity. This is thought to be due to the increase in the volume ratio of the ceramics where the amount of calcium silicate hydrate gel was reduced in relation to the overall volume.     

Interfacial characterisation and mechanical properties of heat treated non-woven kenaf fibre and its reinforced composites

This paper reports on the comprehensive characterisation of heat treated kenaf fibre (KF) and its composites. The kenaf fibres were modified by heating for 2.5–12.5 h inside a drying oven. Heat treatment produces an increase in the crystallinity index and fibre strength of KF. The highest value of KF strength was recorded by applying heat treatment of 10 h on KF. The heat treatment results in the partial removal of impurities/extractives on the KF surface which is detected by scanning electron microscopy and X-ray photoelectron spectroscopy. Atomic force microscopy results signify the decrease of roughness, the increase in peak area density and the increase of the adhesion force on the surface area of heat treated KF. The effect of the heat treatment in enhancing the interface bonding characteristics between the KF and unsaturated polyester matrix can be reflected by the interlaminar shear strength (ILSS) and dynamic mechanical analysis value of the composites. The flexural properties of the composites showed a similar trend to ILSS. However, the fracture toughness revealed contrasting results. Water absorption induced a drastic loss of the mechanical properties of the composites albeit better retention of properties was observed in the case of heat-treated KF composites.     

Electronic and magnetic properties of Ti(2)O(3), Cr(2)O(3), and Fe(2)O(3) calculated by the screened exchange hybrid density functional

The electronic and magnetic properties of the transition metal sesqui-oxides Cr(2)O(3), Ti(2)O(3), and Fe(2)O(3) have been calculated using the screened exchange (sX) hybrid density functional. This functional is found to give a band structure, bandgap, and magnetic moment in better agreement with experiment than the local density approximation (LDA) or the LDA+U methods. Ti(2)O(3) is found to be a spin-paired insulator with a bandgap of 0.22?eV in the Ti d orbitals. Cr(2)O(3) in its anti-ferromagnetic phase is an intermediate charge transfer Mott-Hubbard insulator with an indirect bandgap of 3.31?eV. Fe(2)O(3), with anti-ferromagnetic order, is found to be a wide bandgap charge transfer semiconductor with a 2.41?eV gap. Interestingly sX outperforms the HSE functional for the bandgaps of these oxides.     

Ion synthesis and optical properties of gold nanoparticles in an Al2O3 matrix

Single-crystal Al₂O₃(0001) and Al₂O₃(1120) substrates are implanted by 160-keV Au⁺ ions with doses from 10¹⁵ to 10¹⁷ cm^?2. Some of the implanted samples are air-annealed at 800–1200°C. The properties of the synthesized composite layers are studied by Rutherford backscattering and linear optical reflection measurements, and their nonlinear optical characteristics are examined by RZ-scanning using a picosecond Nd: YAG laser operating at a wavelength of 1064 nm. The Rutherford backscattering spectra indicate that the implanted impurity concentrates near the surface of the Al₂O₃. The formation of gold nanoparticles in the Al₂O₃ can be judged from the characteristic optical plasmon resonance band in the reflectance spectra of the samples irradiated to a dose higher than 6.0 × 10¹⁶ cm^?2. The synthesized particles are shown to be responsible for nonlinear optical refraction in the samples. The nonlinear refractive index, n ₂, and the real part of the third-order susceptibility, Rex⁽³⁾, of the composite layers are determined.     

Electronic transport properties of graphene/Al2O3 (0001) interface

The electronic structure and transport properties of a single layer of graphene (Gr) on α-Al₂O₃ surface are studied using the density functional theory (DFT). We present three models that take into account the atom at the termination of the alumina surface: a) Al atoms, with the center of the Gr hexagon directly over an Al atom; b) Al atoms, with a carbon directly positioned above an Al atom; c) oxygen atoms. Two processes of geometric optimization were used: (i) All the atoms of the supercell were allowed to move in accordance with the BFGS quasi-Newton algorithm; (ii) The atoms of the three topmost layers of the α-Al₂O₃ (0001) slab, including the C atoms, were allowed to move, whereas the atoms of the remaining layers were frozen in their respective atomic bulk positions. The first two models preserve qualitatively the electronic structure of the pristine Gr using the geometric optimization process (i) whereas, in the third model this structure was lost due to a significant charge transfer between the carbon and oxygen atoms irrespective of the optimization procedure. However, models (a) and (b) with the optimization (ii) reveal a p-type semiconducting behavior.     

Effect of bi-layer ratio in ZnO/Al2O3 multilayers on microstructure and functional properties of ZnO nanocrystals embedded in Al2O3 matrix

Zinc oxide (ZnO) nanocrystals (NCs) embedded in alumina (Al₂O₃) matrix were produced via rapid thermal annealing (RTA) of pulsed laser deposited ZnO/Al₂O₃ multilayered nanostructures. The effect of the thickness ratio (R) between Al₂O₃ and ZnO in one bi-layer on the microstructure and functional properties of NCs has been investigated. Grazing incidence small angle X-ray scattering confirmed the formation of nanocrystals after RTA. Grazing incidence wide angle X-ray scattering studies revealed that ZnO NCs have a high crystalline quality with (100) as preferred orientation. Tensile strain of NCs decreases with increasing R and is correlated to the distribution of NCs. From Raman analysis, it is noticed that the phonon frequency of the E₂ mode, related to the ZnO wurtzite phase, in NCs is shifted towards that of bulk ZnO with increasing R. Photoluminescence studies revealed that the near edge peak position shifts from 382 nm to 371 nm as the ratio R changes from 1.5 to 4 and is attributed to the strain effect. The intensity of emission in the yellow–green region due to defects decreases significantly with increasing R. Current–voltage (I–V) characteristics of Al/ZnO NCs embedded in Al₂O₃/n-Si (100)/Al have shown a hysteresis behavior. The increasing width of the hysteresis with increasing R revealed that the origin of the hysteresis might be due to the existence of polar surface charges on well-separated NCs. The high-resistance and low-resistance states in I–V hysteresis curves seem to be governed by Fowler–Nordheim tunneling and Schottky emission mechanisms, respectively.     

Dielectric and photoelectric properties of Pb(Mg1/3Ta2/3O3 crystals

The temperature dependence of the dielectric constant ɛ and the spectral dependence of the photoconductivity of Pb(Mg_1/3Ta_2/3)O₃ crystals are investigated. The width of the band gap (3.4 eV) is determined. It is found that above the temperature of the maximum of the dielectric constant, its reciprocal 1/ɛ varies with temperature first quadratically and then according to a linear law, as is characteristic of ferroelectrics with a smeared phase transition. The smearing parameter of the transition estimated from the experimental data is close to the value calculated assuming the absence of long-range order in the arrangement of the Mg and Ta ions. Fiz. Tverd. Tela (St. Petersburg) 40, 109–110 (January 1998)     

Crystal structure and electromechanical coupling properties of Na0.5Bi2.5Ta2O9 dense ceramics

The crystal structure of sodium bismuth tantalate, Na_0.5Bi_2.5Ta₂O₉, was analyzed by the powder X-ray-diffraction Rietveld method. The distribution of Na atoms was found to be ordered in the A site of the pseudo-perovskite (ATa₂O₇)^2- blocks. The piezoelectric properties were effectively examined using dense bulk ceramics containing manganese oxide as the dopant. The electromechanical coupling coefficients (k_ij) and the electrical quality factors (Q_m) are k_p=10%, k₃₁=8.3%, k_t=19.7%, and Q_m=3000. Received: 1 July 2002 / Accepted: 3 July 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +81-743-726069, E-mail: hiro-t@ms.aist-nara.ac.jp     

Lattice dynamics of sapphire (Al2O3)

Using inelastic neutron scattering we have determined all the dispersion branches of the ₁, ₂ and ₃ representations along the three-fold axis as well as the 2 times 15 branches of ₁ and ₂ symmetry along the -A-direction plus some branches along the -D-direction. The experimental data are analyzed using various rigid ion, polarizable ion and shell models. The shell models give a very satisfactory account of the dispersion curves as well as the scattering intensities. Special attention is given to the investigation of dielectric constants and equilibrium conditions.     

The effect of supports (Al2O3, Al2O3-CeO2 and Al2O3-CeZrO2) on the nature of gold-species in supported gold catalysts

This work is concerned with the study of Au specimens produced by gold deposition on nanosized mixed oxides (alumina, ceria, zirconia) prepared by the sol-gel method using organometallic precursors. According to X-ray absorption near edge structure, extended X-ray absorption fine structure, transmission electron microscopy data, and ultraviolet-visible and X-ray photoelectron spectroscopy measurements, mixed Al-Ce-Zr oxides are quite effective for stabilization of different gold specimens. The samples pre- treated in hydrogen at 150°C are characterized by the presence of gold Au³⁺ cations located on the surface in slightly disordered octahedral oxygen coordination. Metallic gold nanoparticles with a size of about 2 nm and gold clusters were found in the samples treated in hydrogen at 300°C.     

ICP-AES同时测定铬质引流剂中的Cr2O3、Al2O3、Fe2O3和MgO

探讨了电感耦合等离子体-原子发射光谱法(ICP-AES)测定铬质引流剂中Cr2O3、Al2O3、Fe2O3和MgO的分析条件.试样经过氧化钠熔融分解,盐酸酸化,采用内标加入法,利用ICP光谱仪于所推荐的波长处,测量溶液中铬、铝、铁、镁元素对钇内标元素的相对强度,根据标准溶液绘制的校准曲线计算出待测元素氧化物的质量分数.对该方法进行精密度试验,相对标准偏差(RSD,n=8)均小于1.0％,本测试方法简单、快速、精度高,将该方法用于铬质引流剂中Cr2O3、Al2O3、Fe2O3和MgO含量的测定,取得满意效果.     

XPS and auger spectroscopy studies on mixtures of the oxides SiO2, Al2O3, Fe2O3 and Cr2O3

X-ray photoelectron Spectroscopy (XPS) and X-ray-induced Auger Spectroscopy were utilized to examine qualitative and quantitative aspects involved in the surface analysis of mechanical mixtures of the title oxides. Consideration of O1s and OKVV bands of the mixtures makes it possible to distinguish between the single oxide components. The energy shift between the Fe₂O₃ and SiO₂ (or Al₂O₃) components is about twice as large in the OKVV region as in the O1s region. By way of contrast, Auger Spectroscopy analysis of the mixtures does not appear to enable a quantitative distinction between the constituent oxides to be made. Conversely, XPS analysis provides instead quantitative results, although these are affected by a relative error of ± 10%. A simple approach, based on intensity ratio measurements of the single O1s components, enables relatively accurate quantitative results to be obtained.It is shown that analysis of appropriate mixtures is a useful case study for investigations on surface and interface properties of real materials. Argon ion etching effects on the mixtures and on the title oxides analyzed separately are reported.     

Morphology and the magnetic and conducting properties of heterogeneous layered magnetic structures [(Co45Fe45Zr10)35(Al2O3)65/a-Si:H]36

The morphology and the magnetic and conducting properties of an amorphous multilayer nanosystem [(Co₄₅Fe₄₅Zr₁₀)₃₅(Al₂O₃)₆₅/a-Si:H]₃₆ consisting of (Co₄₅Fe₄₅Zr₁₀)₃₅(Al₂O₃)₆₅ magnetic layers and semiconducting hydrogenated amorphous silicon (a-Si:H) layers of various thicknesses have been studied. Using a combination of methods (including polarized neutron reflectometry and grazing incidence small-angle X-ray scattering), it is shown that the magnetic and electrical properties of these multilayer structures are determined by their morphology. It is established that the magnetization and electric resistance of a sample is a nonmonotonic function of the a-Si:H layer thickness. Both characteristics are at a minimum for a structure with a semiconductor layer thickness of 0.4 nm. Samples with silicon layer thicknesses below 0.4 nm represent a three-dimensional structure of Co₄₅Fe₄₅Zr₁₀ grains weakly ordered in space, while in samples with silicon layer thicknesses above 0.4 nm, these grains are packed in layers alternating in the vertical direction. The average lateral distance between nanoparticles in the layer plane has been determined, from which the dimensions of metal grains in each sample have been estimated.     

2E → 4A2 luminescence properties of the hydration isomers of Cr3+ doped K3Al(ox)3

The ²E → ⁴A₂ phosphorescence of Cr(III) doped K₃ [Al(ox)₃] · 3H₂O and partially dehydrated species has been measured between 77 and 4.2°K. Emission in the partially dehydrated crystals is observed from Cr(III) ions in several different sites. In 1% crystals the quantum yield and lifetime both increase on dehydration. Evidence against energy transfer between different sites is offered by the lack of thermalization at 4°K between R lines arising from different sites even at high Cr(III) concentrations, although there is evidence for excitation energy transfer to nonemitting traps.     

Preparation and characterization of ferroelectric SrBi2Ta2O9 thin films on Si using Al2O3 buffer layers

SrBi₂Ta₂O₉ (SBT) thin films were prepared on p-type Si(100) substrates with Al₂O₃ buffer layers. Both the SBT films and the Al₂O₃ buffer layers were deposited by a pulsed laser deposition technique using a KrF excimer laser. An Al prelayer was used to prevent Si surface oxidization in the initial growth stage. It is shown that Al₂O₃ buffer layers effectively prevented interdiffusion between SBT and Si substrates. Furthermore, the capacitance–voltage (C-V) characteristics of the SBT/Al₂O₃/Si heterostructures show a hysteresis loop with a clockwise trace, demonstrating the ferroelectric switching properties of SBT films and showing a memory window of 1.6 V at 1 MHz. Received: 17 July 2000 / Accepted: 16 August 2000 / Published online: 30 November 2000