Initial dislocation density effect on strain hardening in FCC aluminium alloy under laser shock peening

Abstract

The effect of initial dislocation density on subsequent dislocation evolution and strain hardening in FCC aluminium alloy under laser shock peening (LSP) was investigated by using three-dimension discrete dislocation dynamics (DD) simulation. Initial dislocations were randomly generated and distributed on slip planes for three different dislocation densities of 4.21 × 10¹², 8.12 × 10¹² and 1.26 × 10¹³ m^?2. Besides, variable densities of prismatic loops were introduced into the DD cells as nanoprecipitates to study the dislocation pinning effect. The flow stresses as a function of strain rate obtained by DD simulation are compared with relevant experimental data. The results show a significant dislocation density accumulation in the form of dislocation band-like structures under LSP. The overall yield strength in FCC aluminium alloy decreases with increasing initial dislocation density and forest dislocation strengthening becomes negligible under laser induced ultra-high strain rate deformation. In addition, yield strength is enhanced by increasing the nanoprecipitate density due to dislocation pinning effect.     

Modified dislocation filter method: toward growth of GaAs on Si by metal organic chemical vapor deposition

In this paper, metamorphic growth of GaAs on (001) oriented Si substrate, with a combination method of applying dislocation filter layer (DFL) and three-step growth process, was conducted by metal organic chemical vapor deposition. The effectiveness of the multiple InAs/GaAs self-organized quantum dot (QD) layers acting as a dislocation filter was researched in detail. And the growth conditions of the InAs QDs were optimized by theoretical calculations and experiments. A 2-μm-thick buffer layer was grown on the Si substrate with the three-step growth method according to the optimized growth conditions. Then, a 114-nm-thick DFL and a 1-μm-thick GaAs epilayer were grown. The results we obtained demonstrated that the DFL can effectively bend dislocation direction via the strain field around the QDs. The optimal structure of the DFL is composed of three-layer InAs QDs with a growth time of 55 s. The method could reduce the etch pit density from about 3 × 10⁶ cm^?2 to 9 × 10⁵ cm^?2 and improve the crystalline quality of the GaAs epilayers on Si.     

Surface modification and adhesion of wood-plastic composite (WPC) treated with UV/ozone

Because of the surfaces of wood-plastic composite (WPC) materials are enriched in polymers of low surface energy, they exhibit low adhesion properties. UV/ozone is proposed as surface treatment for increasing the surface energy and adhesion of WPC materials made with different polymers (polyethylene, polypropylene and polyvinyl chloride). UV lamp-WPC surface distance and time of UV exposure were varied for optimizing UV/ozone treatment of WPC, and UV dose used ranged between 2.02 × 10^?14 and 5.05 × 10^?12 J·s/m². UV/ozone treatment created new carbon-oxygen polar groups in WPC surfaces and increased their surface energy, mainly their polar component. Furthermore, ablation of the outermost WPC surface was produced, more noticeably by reducing the distance between WPC surface and UV lamp and by increasing the duration of the treatment. Noticeable increase in 180° peel adhesion was obtained in the joints made with UV/ozone treated WPC at 10–30 mm distance during 1–5 min (i.e., UV dose between 5.61 × 10^?14 and 2.53 × 10^?12 J·s/m²). Although 180° peel strength of joints made with acrylic adhesive tape and UV/ozone treated WPC for 10 min and 10 mm distance (UV dose: 5.05 × 10^?12 J·s/m²) was not increased because of dominant effect of ablation over creation of polar groups, the cross-hatch adhesion to different coatings was highly improved, irrespective of the polymer used and the wood content of WPC; however, the surface modifications and adhesion of UV/ozone treated WPC were more marked when its wood content was higher and by using UV dose between 0.10 × 10^?12 and 2.53 × 10^?12 J·s/m².     

Studies of some physical properties of PrFe0.7Ni0.3O3 thin films after 200 MeV Ag15+ irradiation

PrFe_0.7Ni_0.3O₃ thin films (thickness ~ 200 nm) were prepared by pulsed laser ablation technique on LaAlO₃ substrate. These films were irradiated with 200?MeV Ag¹⁵⁺ ions at various fluencies, ranging from 1 × 10¹¹ to 1 × 10¹² ions/cm². These irradiated thin films were characterized by using X-ray diffraction, dc conductivity, dc magnetization and atomic force microscopy. These films exhibit orthorhombic structure and retain it even after irradiations. The crystallite size (110–137?nm), micro strain (1.48 × 10^?2–1.75 × 10^?2 line^?2?m^?4) and dislocation density (79.7 × 10¹⁴–53.2 × 10¹⁴ line/m²) vary with ion fluencies. An enhancement in resistivity at certain fluence and then a decrease in its value (0.22175–0.21813?Ω?cm) are seen. A drastic change in observed magnetism after ion irradiation is seen. With ion irradiation, an increase in surface roughness, due to the formation of hillocks and other factors, is observed. Destruction of magnetic domains after irradiation can also be visualized with magnetic force microscopy and is in close agreement with magnetization data. The impact on various physical properties in these thin films after irradiation indicates a distortion in the lattice structure and consequently on single-particle band width caused by stress-induced defects.     

Effects of the AlN nucleation layer thickness on the crystal structures of an AlN epilayer grown on the 6H-SiC substrate

The influence of the LT-AlN(NL) growth times on the mosaic structure parameters of the AlN layer grown on the LT-AlN(NL)/6H-SiC structures as well as the dislocation densities and the strain behaviours in the AlN epilayers has been investigated using XRD measurements. The growth times of the LT-AlN(NL) were changed to 0, 60, 120, 180, and 240?s. We observed that the mosaic structure parameters of the AlN epilayers were slightly affected by the LT-AlN(NL) growth times. However, the dislocation densities in the AlN layer are affected by the growth times of the LT-AlN(NL) layer. The highest edge dislocation density (5.48?×?10¹⁰?±?2.3?×?10⁹?cm^?2) was measured for the sample in which 120?s grown LT-AlN(NL) was used. On the other hand, highest screw type dislocation density (1.21?×?10¹⁰?±?1.7?×?10⁹?cm^?2) measured in the sample E that contains 240?s growth LT-AlN(NL). The strain calculation results show that the samples without LT-AlN(NL) suffered maximum compressive in-plane strain (?10.9?×?10^?3?±?1.8?×?10^?4), which can be suppressed by increasing the LT-AlN(NL) growth times. The out-of-plane strain also has a compressive character and its values increase with LT-AlN(NL) growth times between 60 and 180?s. Same out-of-plane strain values were measured for the LT-AlN(NL) growth times of 180 and 240?s. Furthermore, the form of the biaxial stress in the AlN epilayer changed from compressive to tensile when the LT-AlN(NL) growth times were greater than 120?s.     

Growth of high-quality ZnO thin films on (11\bar{2}0) a-plane sapphire substrates by plasma-assisted molecular beam epitaxy

High-quality ZnO thin films were grown on a-plane sapphire substrates by plasma-assisted molecular beam epitaxy. X-ray diffraction and transmission electron microscopy reveal that the ZnO films have high structural quality and an atomically sharp ZnO/Al₂O₃ interface. The full width at half maximum values of the 0002 and $30\bar{3}2$ ZnO ω-rocking curves are 467.8 and 813.5 arc sec for a 600 nm thick ZnO film. A screw dislocation density of 4.35×10⁸ cm^?2 and an edge dislocation density of 3.38×10⁹ cm^?2 are estimated by X-ray diffraction. The surface of the ZnO epilayers contains hexagonal pits, which can be observed in the Zn-polar ZnO. The films have a resistivity of 0.119 Ω?cm, an electron concentration of 6.85×10¹⁷ cm^?3, and a mobility of 76.5 cm²?V^?1?s^?1 at room temperature. Low temperature photoluminescence measurements show good optical properties comparable to ZnO single crystals.     

质子辐照对纯铝薄膜微观结构的影响

利用透射电子显微镜(TEM)详细分析了不同剂量的质子辐照纯铝薄膜样品的微观结构, 质子的能量E=160 keV.实验表明,质子辐照能够在Al薄膜中诱发空位位错圈,在实验范围内,位错密度随辐照剂量的增加而增加;质子辐照在1×10¹¹—4×10¹¹/mm²范围内随辐照剂量的增加,位错圈数量密度以及位错圈尺寸都随之增加.在较高剂量6×10¹¹/mm²辐照下,位错圈数量密度减小,但其尺寸显著 关键词： 质子辐照 空位簇缺陷 位错圈 微观结构     

Estimation of microbial methane generation and oxidation rates in the municipal solid waste landfill of Kaluga city,Russia

Using a theoretical model and mass isotopic balance, biogas (methane and CO₂) released from buried products at their microbial degradation was analysed in the landfill of municipal and non-toxic industrial solid organic waste near Kaluga city, Russia. The landfill contains about 1.34×10⁶ tons of waste buried using a ‘sandwich technique’ (successive application of sand–clay and waste layers). The δ¹³C values of biogenic methane with respect to CO₂ were?56.8 (±2.5) ‰, whereas the δ¹³C of CO₂ peaked at+9.12‰ (+1.4±2.3‰ on average), reflecting a virtual fractionation of carbon isotopes in the course of bacterial CO₂ reduction at the landfill body. After passing through the aerated soil layers, methane was partially oxidised and characterised by δ¹³C in the range of?50.6 to?38.2‰, evidencing enrichment in ¹³C, while the released carbon dioxide had δ¹³C of?23.3 to?4.04‰, respectively. On the mass isotopic balance for the δ¹³C values, the methane production in the landfill anaerobic zone and the methane emitted through the aerated landfill surface to the atmosphere, the portion of methane oxidised by methanotrophic bacteria was calculated to be from 10 to 40% (averaged about 25%). According to the theoretical estimation and field measurements, the annual rate of methane production in the landfill reached about 2.9(±1.4)×10⁹ g C CH₄ yr^?1 or 5.3(±2.6)×10⁶ m³ CH₄ yr^?1. The average rates of methane production in the landfill and methane emission from landfill to the atmosphere are estimated as about 53 (±26) g C CH₄ m^?2 d^?1 (or 4 (±2) mol CH₄ m^?2 d^?1) and 33 (±12) g C CH₄ m^?2 d^?1 (or 2.7 (±1) mol CH₄ m^?2 d^?1), respectively. The calculated part of methane consumed by methanotrophic bacteria in the aerated part of the landfill was 13(±7) g C CH₄ m^?2 d^?1 (or 1.1(±0.6) mol CH₄ m^?2 d^?1) on average.     

入射电子能量对低密度聚乙烯深层充电特性的影响

高能带电粒子与航天器介质材料相互作用引起的深层带电现象, 一直是威胁航天器安全运行的重要因素之一. 考虑入射电子在介质中的电荷沉积、能量沉积分布以及介质中的非线性暗电导和辐射诱导电导, 建立了介质深层充电的单极性电荷输运物理模型. 通过求解电荷连续性方程和泊松方程, 可以得出不同能量 (0.1–0.5 MeV) 电子辐射下, 低密度聚乙烯 (厚度为1 mm) 介质中的电荷输运特性. 计算结果表明, 不同能量的电子辐射下, 介质充电达到平衡时, 最大电场随入射能量的增加而减小; 同一能量辐射下, 最大电场随束流密度的增大而增加. 入射电子能量较低时 (≤ 0.3 MeV) , 最大电场随束流密度的变化趋势基本相同. 具体表现为: 当束流密度大于3× 10^-9 A/m²时, 最大场强超过击穿阈值2×10⁷ V/m, 发生静电放电 (ESD) 的可能性较大. 随着入射电子能量的增加, 发生静电放电 (ESD) 的临界束流密度增大, 在能量为0.4 MeV时, 临界束流密度为6×10^-8 A/m². 当能量大于等于0.5 MeV时, 在束流密度为10^-9–10^-6 A/m²的范围内, 均不会发生静电放电 (ESD) . 该物理模型对于深入研究深层充放电效应、评估航天器在空间环境下 深层带电程度及防护设计具有重要的意义. 关键词： 高能电子辐射 低密度聚乙烯(LDPE) 介质深层充电 电导特性     

Molecular dynamics simulation of methane in sodium montmorillonite clay hydrates at elevated pressures and temperatures

Computer simulation has been used to study the structure and dynamics of methane in hydrated sodium montmorillonite clays under conditions encountered in sedimentary basins. Systems containing approximately one, two, three and four molecuiar layers of water have followed gradients of 150 bar km^?1 and 30Kkm^?1, to a maximum burial depth of 6 km (900 bar and 460 K). Methane is coordinated to approximately 19 oxygen atoms, of which typically 6 are provided by the clay surface. Only in the three- and four-layer hydrates is methane able to leave the clay surface. Diffusion depends strongly on the porosity (water content) and burial deth self-diffusion coefficients are in the range 0.12 × 10^?9m²S^?1 < D < 12.65 × 10^?9m²s^?1 for water and 0.04 × 10^?9m²s^?1 < D < 8.64 × 10^?9m²s^?1 for methane. Bearing in mind that porosity decreases with burial depth, it is estimated that maximum diffusion occurs at around 3 km. This is in good agreement with the known location of methane reservoirs in sedimentary basins.     

Electrical characteristics of GaAs MOS capacitor and field effect transistor with atomic layer-deposited TiO2/Al2O3 dielectrics

The (NH₄)₂S treatment can reduce native oxides and passivate GaAs. Atomic layer-deposited Al₂O₃ can further remove the residue native oxides by self-cleaning. Stacked with high dielectric constant TiO₂ prepared by atomic layer deposition on Al₂O₃/(NH₄)₂S-treated GaAs MOS capacitor, the leakage current densities can reach 4.5 × 10^?8 and 3.4 × 10^?6 A/cm² at ±2 MV/cm. The net effective dielectric constant of the entire stack is 18 and the interface state density is about 4.2 × 10¹¹/cm²/eV. The fabricated enhancement-mode n-channel GaAs MOSFET exhibited good electrical characteristics with a maximum g _m of 122 mS/mm and electron mobility of 226 cm²/V s.     

Charge carriers dynamics in PEO + NaSCN polymer electrolytes

Sodium-ion-conducting poly(ethylene oxide) (PEO)-based solid polymer electrolyte films mixed with salt sodium thiocyanate (NaSCN) have been prepared by solution-cast method. Films were characterized in detail using optical microscopy, differential scanning calorimetry, and impedance spectroscopy. The drop in ionic conductivity with increasing salt concentration is supported by a decrease in number of charge carriers. Dielectric constant is supported by decreases in numbers of charge carriers and increase in mobility. The maximum ionic conductivity and number of charge carriers for material are found 9.86 × 10^?6 S/m and 1.21 × 10²⁰, respectively, for weight % ratio (95:05) of PEO:NaSCN polymer salt complex. The maximum mobility of material is found 2.58 × 10^?6 m²/Vs for weight % ratio (80:20) of PEO:NaSCN polymer salt complex.     

Linear and nonlinear optical properties of rare earth doped of Ba0.7Sr0.3TiO3 thin films

Ba_0.7Sr_0.3TiO₃:Eu ferroelectric films were deposited on quartz substrates by pulsed laser deposition. The linear absorption coefficient and the linear refractive index calculated from the transmission spectrum at 532 nm were found to be 1.67×10⁴ cm^?1 and 1.82 respectively. The room temperature photoluminescence shows the characteristic emission of Eu³⁺ ions. The nonlinear optical properties of the film were investigated by a single beam Z-scan setup. The negative nonlinear refractive index and two photon absorption coefficient was found to be ?1.508×10^?6 m²/GW and 240 m/GW respectively. The real and imaginary part of the third order susceptibility of the thin films is 2.58×10^?17 m²/V² and 1.16×10^?16 m²/V² respectively. The BST:Eu thin films show good optical limiting property.     

Aerosol characterization and lung deposition of synthesized TiO2 nanoparticles for murine inhalation studies

This study presents a novel exposure protocol for synthesized nanoparticles (NPs). NPs were synthesized in gas phase by thermal decomposition of metal alkoxide vapors in a laminar flow reactor. The exposure protocol was used to estimate the deposition fraction of titanium dioxide (TiO₂) NPs to mice lung. The experiments were conducted at aerosol mass concentrations of 0.8, 7.2, 10.0, and 28.5 mg m^?3. The means of aerosol geometric mobility diameter and aerodynamic diameter were 80 and 124 nm, and the geometric standard deviations were 1.8 and 1.7, respectively. The effective density of the particles was approximately from 1.5 to 1.7 g cm^?3. Particle concentration varied from 4 × 10⁵ cm^?3 at mass concentrations of 0.8 mg m^?3 to 12 × 10⁶ cm^?3 at 28.5 mg m^?3. Particle phase structures were 74% of anatase and 26% of brookite with respective crystallite sized of 41 and 6 nm. The brookite crystallites were approximately 100 times the size of the anatase crystallites. The TiO₂ particles were porous and highly agglomerated, with a mean primary particle size of 21 nm. The specific surface area of TiO₂ powder was 61 m² g^?1. We defined mice respiratory minute volume (RMV) value during exposure to TiO₂ aerosol. Both TiO₂ particulate matter and gaseous by-products affected respiratory parameters. The RMV values were used to quantify the deposition fraction of TiO₂ matter by using two different methods. According to individual samples, the deposition fraction was 8% on an average, and when defined from aerosol mass concentration series, it was 7%. These results show that the exposure protocol can be used to study toxicological effects of synthesized NPs.     

Superior tolerance of Ag/Ni multilayers against Kr ion irradiation: an in situ study

Monolithic Ag and Ni films and Ag/Ni multilayers with individual layer thickness of 5 and 50?nm were subjected to in situ Kr ion irradiation at room temperature to 1 displacement-per-atom (a fluence of 2?×?10¹⁴?ions/cm²). Monolithic Ag has high density of small loops (4?nm in diameter), whereas Ni has fewer but much greater loops (exceeding 20?nm). In comparison, dislocation loops, ～4?nm in diameter, were the major defects in the irradiated Ag/Ni 50?nm film, while the loops were barely observed in the Ag/Ni 5?nm film. At 0.2?dpa (0.4?×?10¹⁴?ions/cm), defect density in both monolithic Ag and Ni saturated at 1.6 and 0.2?×?10²³/m³, compared with 0.8?×?10²³/m³ in Ag/Ni 50?nm multilayer at a saturation fluence of ～1?dpa (2?×?10¹⁴?ions/cm²). Direct observations of frequent loop absorption by layer interfaces suggest that these interfaces are efficient defect sinks. Ag/Ni 5?nm multilayer showed a superior morphological stability against radiation compared to Ag/Ni 50?nm film.     

Determination of elastic strain fields and geometrically necessary dislocation distributions near nanoindents using electron back scatter diffraction

The deformation around a 500-nm deep Berkovich indent in a large grained Fe sample has been studied using high resolution electron back scatter diffraction (EBSD). EBSD patterns were obtained in a two-dimensional map around the indent on the free surface. A cross-correlation-based analysis of small shifts in many sub-regions of the EBSD patterns was used to determine the variation of elastic strain and lattice rotations across the map at a sensitivity of ～±10^?4. Elastic strains were smaller than lattice rotations, with radial strains found to be compressive and hoop strains tensile as expected. Several analyses based on Nye's dislocation tensor were used to estimate the distribution of geometrically necessary dislocations (GNDs) around the indent. The results obtained using different assumed dislocation geometries, optimisation routines and different contributions from the measured lattice rotation and strain fields are compared. Our favoured approach is to seek a combination of GND types which support the six measurable (of a possible nine) gradients of the lattice rotations after correction for the 10 measurable elastic strain gradients, and minimise the total GND line energy using an L¹ optimisation method. A lower bound estimate for the noise on the GND density determination is ～±10¹² m^?2 for a 200-nm step size, and near the indent densities as high as 10¹⁵ m^?2 were measured. For comparison, a Hough-based analysis of the EBSD patterns has a much higher noise level of ～±10¹⁴m^?2 for the GND density.     

Transport properties of n-type ferromagnetic semiconductor HgCr2−xInxSe4(x = 0.100)

Measurements of the electrical conductivity, magnetoresistance, and Hall effect were performed on a n-type ferromagnetic semiconductor HgCr_2?xIn_xSe₄(x = 0.100) single crystal from 6.3 to 296 K in magnetic fields up to 1.19×l0⁶A/m. The conductivity decreases rapidly near the Curie temperatureT_c (≈120 K) as the temperature is raised. A large peak in the magnetoresistance is observed near T_c. The Hall effect measurements indicate that the temperature dependence of the conductivity and the magnetoresistance are due mostly to a change in electron mobility. The electron mobility is 1.2 × 10^?2 m²/V · s at 6.3 K, and decreases rapidly near T_c with the rise in temperature. Then it increases slowly from 5.5 × 10^?4 m²/V · s at 160 K to 7.5 × 10^?4 m²/V · s at 241 K. This temperature dependence of the electron mobility can be explained in terms of the spin-disorder scattering which takes into account the exchange interaction between charge carriers and localized magnetic moments.     

Radiative transition of hydrogen-like ions in quantum plasma

At fusion plasma electron temperature and number density regimes of 1?×?10³–1?×?10⁷?K and 1?×?10²⁸–1?×?10³¹/m³, respectively, the excited states and radiative transition of hydrogen-like ions in fusion plasmas are studied. The results show that quantum plasma model is more suitable to describe the fusion plasma than the Debye screening model. Relativistic correction to bound-state energies of the low-Z hydrogen-like ions is so small that it can be ignored. The transition probability decreases with plasma density, but the transition probabilities have the same order of magnitude in the same number density regime.     

Electrically stimulated movement of edge dislocations in silicon in the temperature range 300–450 K

The movement of edge dislocations and the related acoustic emission of Si (111) carrying a direct current of density 0.5?5×10⁵ A/m² in the [110] direction are studied in the temperature range T=300–450 K. It is shown that the basic mechanism of dislocation movement is the electric wind determining the magnitude of the effective charge (per atom of the dislocation line) Z _eff=0.06 (n-Si) and ?0.01 (p-Si). Matching theory with experimental data has made it possible to determine the main contribution of edge dislocations to the acoustic-emission response of the silicon samples under investigation. The characteristic transition frequencies of dislocations in n-and p-Si from one metastable state into another are found to be f _max=0.1–0.5 Hz. The numerical values of the diffusion coefficient for atoms in the dislocation impurity atmosphere are estimated as 3.2×10^?18 m²/s (n-Si) and 1.5×10^?18 m²/s (p-Si).     

Comparative Study on Three Different Systems of Chemiluminescence Flow‐Injection Determination of Leucogen

Abstract

The effects of three systems on the chemiluminescence (CL) intensity have been studied in this paper, such as leucogen–potassium permanganate–rhodamine B, leucogen–cerium (IV)–rhodamine B, and leucogen–luminol–hydrogen peroxide (called system 1, system 2, and system 3, respectively). The mechanism of these reactions is also discussed. Surfactant (CTMAB) has a remarkably sensitive effect on these systems mentioned above. Therefore, three new flow injection chemiluminescence methods for the determination of leucogen have been established. For system 1, the linear range is 8.0×10^?8 to 4.0×10^?5 g mL^?1, with limits of detection 2×10^?8 g mL^?1; the relative standard deviation is 2.5% (n=11, Cs=4.0×10^?6 g mL^?1). For system 2, the linear range is 1.0×10^?8 to 5.0×10^?6 g mL^?1, with limits of detection 3×10^?9 g mL^?1; the relative standard deviation is 5.1% (n=11, Cs=1.0×10^?6 g mL^?1). For system 3, the linear range is 4.0×10^?8 to 2.0×10^?6 g mL^?1, with limits of detection 1×10^?8 g mL^?1; the relative standard deviation is 1.3% (n=11, Cs=1.0×10^?7 g mL^?1). Compared with the three methods above, system 3 is confirmed as the best method. This method has been applied to the determination of leucogen with satisfactory results.