航空铝合金7050-T7451高速切削加工中流动应力模型

通过对分离式Hopkinson压杆进行高温动态压缩实验,得到在冲击压缩中材料航空铝合金7050-T7451在室温到高温550℃的应变、应变率与应力间的数据依赖关系.利用高速切削实验及有限元模拟相结合对该数据关系进行修正以适合高速切削加工的"高温"、"高应变率"及"大应变"状态.选择综合考虑温度软化效应,应变强化和应变率强化效应的经验Johnson-Cook模型,对其数据关系进行量化的描述,并确定铝合金7050-T7451流动应力本构模型中材料常数的值,最后建立了铝合金7050-T7451的本构模型.以实验和模拟中输出主切削力为比较指标,验证了所建模型的正确性.     

含三唑复合防腐剂及其竹处理材的金属腐蚀性能

目的探究三唑复合防腐剂及其竹处理材对金属连接件的腐蚀性和适用性,为选择处理设备材质和竹处理材防水涂层提供参考。方法参考GB/T 34726—2017《木材防腐剂对金属的腐蚀速率测定方法》和GB/T 34724—2017《接触防腐木材的金属腐蚀速率加速测定方法》标准,测定复合防腐剂（有效成分:丙环唑?戊唑醇（PPZ-TEB）、碘丙炔基正丁氨基甲酸酯（IPBC）、异噻唑啉酮（CMIT-MIT））及其毛竹处理材对Q235碳钢、65Mn弹簧钢、304不锈钢、201不锈钢、H59黄铜、T2紫铜、7075铝合金和6061铝合金的金属腐蚀性。通过在竹材?金属组件表面涂刷水性聚氨酯漆、水性丙烯酸漆和木蜡油考察表面涂饰对防腐蚀效果的影响。结果（1）经复合防腐剂浸泡加速腐蚀后,304不锈钢、201不锈钢、6061铝合金和7075铝合金的金属腐蚀速率均为0;Q235碳钢和65Mn弹簧钢的金属腐蚀速率随时间增加保持不变,且腐蚀速率离散性前期较大,后期逐渐减小;H59黄铜和T2紫铜在制剂A（PPZ-TEB）、C（PPZ-TEB/CMIT-MIT）、CK₁（CMIT-MIT）和CK₂（素材）中浸泡腐蚀和与竹处理材接触腐蚀的金属腐蚀速率均为0,而浸泡在制剂B（PPZ-TEB/IPBC）中发生轻微腐蚀。（2）在与竹处理材接触加速腐蚀后,304不锈钢、201不锈钢、H59黄铜和T2紫铜的金属腐蚀速率为0;Q235碳钢和65Mn弹簧钢腐蚀速率随时间增加而减小并趋于平缓,且腐蚀程度明显大于防腐剂对金属的腐蚀;6061铝合金和7075铝合金发生轻微腐蚀。（3）不同复合制剂及其竹处理材对Q235碳钢和65Mn弹簧钢的腐蚀性分别为CK₁ > C > B > A > CK₂,C > CK₁ > B > A > CK₂。（4）在Q235碳钢和65Mn弹簧钢的竹材?金属组件表面涂饰水性聚氨酯漆、水性丙烯酸漆和木蜡油涂层后,竹处理材的金属腐蚀速率均有所下降,且木蜡油较水性聚氨酯漆和水性丙烯酸漆的防腐蚀效果更优。结论含三唑复合防腐剂及其竹处理材对304不锈钢和201不锈钢均无腐蚀。复合防腐剂及其竹处理材对H59黄铜和T2紫铜基本无腐蚀。复合防腐剂对Q235碳钢和65Mn弹簧钢的腐蚀速率随时间增加保持不变,而竹处理材腐蚀速率随时间增加而减小并趋于平缓,且前者小于后者。复合防腐剂对7075铝合金和6061铝合金无腐蚀,而竹处理材有轻微腐蚀。不同复合制剂及其竹处理材对Q235碳钢和65Mn弹簧钢的腐蚀性均为C > B > A。表面涂饰可降低竹处理材对金属的腐蚀性。      

Deposition of conformal copper and nickel films from supercritical carbon dioxide

Device-quality copper and nickel films were deposited onto planar and etched silicon substrates by the reduction of soluble organometallic compounds with hydrogen in a supercritical carbon dioxide solution. Exceptional step coverage on complex surfaces and complete filling of high-aspect-ratio features of less than 100 nanometers width were achieved. Nickel was deposited at 60 degrees C by the reduction of bis(cyclopentadienyl)nickel and copper was deposited from either copper(I) or copper(II) compounds onto the native oxide of silicon or metal nitrides with seed layers at temperatures up to 200 degrees C and directly on each surface at temperatures above 250 degrees C. The latter approach provides a single-step means for achieving high-aspect-ratio feature fill necessary for copper interconnect structures in future generations of integrated circuits.     

Plastic deformation recovery in freestanding nanocrystalline aluminum and gold thin films

In nanocrystalline metals, lack of intragranular dislocation sources leads to plastic deformation mechanisms that substantially differ from those in coarse-grained metals. However, irrespective of grain size, plastic deformation is considered irrecoverable. We show experimentally that plastically deformed nanocrystalline aluminum and gold films with grain sizes of 65 nanometers and 50 nanometers, respectively, recovered a substantial fraction (50 to 100%) of plastic strain after unloading. This recovery was time dependent and was expedited at higher temperatures. Furthermore, the stress-strain characteristics during the next loading remained almost unchanged when strain recovery was complete. These observations in two dissimilar face-centered cubic metals suggest that strain recovery might be characteristic of other metals with similar grain sizes and crystalline packing.     

High Critical-Current Density in the Heavily Pb-Doped Bi2Sr2CaCu2O8+delta Superconductor: Generation of Efficient Pinning Centers

Critical-current density (Jc) is a parameter of primary importance for potential applications of high-temperature copper oxide superconductors. It is limited principally by the breakdown of zero-resistive current due to thermally activated flux flow at high temperatures and high magnetic fields. One promising method to overcome this limitation is to introduce efficient pinning centers into crystals that can suppress the flux flow. A marked increase in Jc was observed in Bi2Sr2CaCu2O8+delta (Bi-2212) single crystals doped with a large amount of Pb. By electron microscopy, characteristic microstructures were revealed that probably underlie the observed enhancement in Jc: thin (10 to 50 nanometers), platelike domains having a modulation-free structure appeared with spacings of 50 to 100 nanometers along the b axis.     

Superplastic extensibility of nanocrystalline copper at room temperature

A bulk nanocrystalline (nc) pure copper with high purity and high density was synthesized by electrodeposition. An extreme extensibility (elongation exceeds 5000%) without a strain hardening effect was observed when the nc copper specimen was rolled at room temperature. Microstructure analysis suggests that the superplastic extensibility of the nc copper originates from a deformation mechanism dominated by grain boundary activities rather than lattice dislocation, which is also supported by tensile creep studies at room temperature. This behavior demonstrates new possibilities for scientific and technological advancements with nc materials.     

A maximum in the strength of nanocrystalline copper

We used molecular dynamics simulations with system sizes up to 100 million atoms to simulate plastic deformation of nanocrystalline copper. By varying the grain size between 5 and 50 nanometers, we show that the flow stress and thus the strength exhibit a maximum at a grain size of 10 to 15 nanometers. This maximum is because of a shift in the microscopic deformation mechanism from dislocation-mediated plasticity in the coarse-grained material to grain boundary sliding in the nanocrystalline region. The simulations allow us to observe the mechanisms behind the grain-size dependence of the strength of polycrystalline metals.     

铝合金桥面板合理断面形式拓扑分析和优化

在简要综述铝合金桥梁桥面板结构形式的基础上,利用ANSYS拓扑技术进行铝合金桥梁桥面板结构形式的拓扑优化分析,得到铝合金桥面板的概念模型;考虑铝合金桥面板的强度和刚度要求以及铝合金挤压生产能力,设计了两种铝合金桥面板,并对所设计的2种铝合金桥面板细部尺寸进行了优化分析.研究表明,采用ANSYS拓扑得到的铝合金桥面板具有足够的刚度,可以满足公路桥梁荷载的要求;不同荷载工况下两种铝合金桥面板的整体刚度比较接近,无竖向支撑的铝合金桥面板的刚度要略大于有竖向支撑的铝合金桥面板.     

Boron nitride nanotubes

The successful synthesis of pure boron nitride (BN) nanotubes is reported here. Multi-walled tubes with inner diameters on the order of 1 to 3 nanometers and with lengths up to 200 nanometers were produced in a carbon-free plasma discharge between a BN-packed tungsten rod and a cooled copper electrode. Electron energy-loss spectroscopy on individual tubes yielded B:N ratios of approximately 1, which is consistent with theoretical predictions of stable BN tube structures.     

Three-dimensional orientation mapping in the transmission electron microscope

Over the past decade, efforts have been made to develop nondestructive techniques for three-dimensional (3D) grain-orientation mapping in crystalline materials. 3D x-ray diffraction microscopy and differential-aperture x-ray microscopy can now be used to generate 3D orientation maps with a spatial resolution of 200 nanometers (nm). We describe here a nondestructive technique that enables 3D orientation mapping in the transmission electron microscope of mono- and multiphase nanocrystalline materials with a spatial resolution reaching 1 nm. We demonstrate the technique by an experimental study of a nanocrystalline aluminum sample and use simulations to validate the principles involved.     

Three-dimensional atomic-scale imaging of impurity segregation to line defects

Clouds of impurity atoms near line defects are believed to affect the plastic deformation of alloys. Three-dimensional atom probe techniques were used to image these so-called Cottrell atmospheres directly. Ordered iron-aluminum alloys (40 atomic percent aluminum) doped with boron (400 atomic parts per million) were investigated on an atomic scale along the <001> direction. A boron enrichment was observed in the vicinity of an <001> edge dislocation. The enriched region appeared as a three-dimensional pipe 5 nanometers in diameter, tangent to the dislocation line. The dislocation was found to be boron-enriched by a factor of 50 (2 atomic percent) relative to the bulk. The local boron enrichment is accompanied by a strong aluminum depletion of 20 atomic percent.     

Deformation twinning in nanocrystalline aluminum

We report transmission electron microscope observations that provide evidence of deformation twinning in plastically deformed nanocrystalline aluminum. The presence of these twins is directly related to the nanocrystalline structure, because they are not observed in coarse-grained pure aluminum. We propose a dislocation-based model to explain the preference for deformation twins and stacking faults in nanocrystalline materials. These results underscore a transition from deformation mechanisms controlled by normal slip to those controlled by partial dislocation activity when grain size decreases to tens of nanometers, and they have implications for interpreting the unusual mechanical behavior of nanocrystalline materials.     

盾叶薯蓣根茎中薯蓣皂甙元的分布

研究了薯蓣皂甙元在多年生的盾叶薯蓣根茎中不同部位的分布,结果表明,薯蓣皂甙元在根茎中的分布具有不均匀性,嫩茎顶端薯蓣皂甙元的含量最高,抽茎区段次之,接着是嫩茎区段,底层区段的含量最低,而人们通常认为含量高的老茎区段其含量只比腐烂区段和底层区段高。说明在同一根茎中,代谢旺盛的部位其薯蓣皂甙元的含量比代谢微弱的部位要高。此外,还对地上茎基部、根茎上须根的薯蓣皂甙元的含量与各根茎区段作了比较。同时发现,根茎中除嫩茎顶端外,各区段的水分百分含量没有明显差异。     

Solar constant: first direct measurements

The solar constant was directly measured from an altitude of about 82 kilometers-apparently the first such determination. The total solar intensity was 136.1 milliwatts per square centimeter, or 1.952 calories per square centimeter, per minute-about 2.5 percent less than Johnson's derived value. Energy in the ultraviolet and visible regions (for lambda less than 607 nanometers) was 7.0 percent less than that obtained by integration over Johnson'Scurve; for integral flux of lambda greater than 607 nanometers there was almost perfect agreement. Seven supporting series of measurements from lower altitudes agreed extremely well with these results after correction for atmospheric extinction.     

铝毒害对毛竹笋铜元素含量的影响

以福建省桐口国有林场毛竹林为研究对象,通过研究铜元素对铝毒害之响应,以期了解铝毒害对毛竹笋品质的影响。采用回归旋转组合设计进行毛竹林铝毒害的田间试验。统计分析表明土壤酸性和A l离子浓度对毛竹笋铜元素含量有显著影响,且其影响在第1年呈负相关关系,随着时间的推移,到第2年呈正相关关系。A l离子处理对毛竹笋Cu元素含量前期呈抑制作用;随着时间的推移,土壤中的A l离子浓度持续下降,到第2年A l离子对Cu元素含量呈促进作用,Cu元素含量显著增加。     

Supernova olivine from cometary dust

An interplanetary dust particle contains a submicrometer crystalline silicate aggregate of probable supernova origin. The grain has a pronounced enrichment in 18O/16O (13 times the solar value) and depletions in 17O/16O (one-third solar) and 29Si/28Si (<0.8 times solar), indicative of formation from a type II supernova. The aggregate contains olivine (forsterite 83) grains <100 nanometers in size, with microstructures that are consistent with minimal thermal alteration. This unusually iron-rich olivine grain could have formed by equilibrium condensation from cooling supernova ejecta if several different nucleosynthetic zones mixed in the proper proportions. The supernova grain is also partially encased in nitrogen-15-rich organic matter that likely formed in a presolar cold molecular cloud.     

铜离子吸附对可变电荷土壤与恒电荷土壤铝释放的影响

研究了两种可变电荷土壤和两种恒电荷土壤在不同铜离子浓度条件下,pH对铝释放的影响.结果显示,随着加入铜离子浓度的增加,由铜离子交换作用而引起的可溶性铝也随之增加,相同pH条件下,可溶性铝的解吸量依次为砖红壤＞红壤＞黄棕壤＞棕壤,恒电荷土壤中铜离子浓度变化对铝释放的影响较可变电荷土壤更大,当pH大于3.6(恒电荷土壤)或pH大于4.0(可变电荷土壤)时,溶液中可溶性铝的含量几乎可以忽略不计.因此在所研究的铜离子浓度范围内,引起可溶性铝离子量变化的主导因素应该是体系pH值的变化而非铜离子的吸附.     

仁用杏叶不同生育时期主要保护酶活性的变化规律

[目的]研究仁用杏的抗逆性机理。[方法]以5年生发育良好的仁用杏苗木的叶片为试验材料,于硬化期、生长初期和速生期对仁用杏苗木进行铜、锌喷雾处理,采用NBT还原法和邻苯二酚法分别对仁用杏叶片的多酚氧化酶(PPO)活性和超氧化物歧化酶(SOD)活性进行测定,分析了仁用杏叶中主要保护酶PPO和SOD的酶活性在不同生育时期的变化规律。[结果]仁用杏叶经Cu(3)Zn(0)处理后PPO活性显著提高,且在硬化期也保持较高的水平。仁用杏叶经Cu(0)Zn(3)处理后PPO活性的增强很小甚至表现负作用。仁用杏叶经过Cu(0)Zn(3)处理后SOD的活性有显著提高,生长初期的SOD活性明显高于硬化期和速生期。[结论]锌对仁用杏叶内SOD的活性的增强作用比较显著,铜、锌通过PPO和SOD的活性的改变影响仁用杏苗木生长,从而提高苗木抗逆性。     

铜离子吸附对可变电荷土壤与恒电荷土壤铝释放的影响

研究了两种可变电荷土壤和两种恒电荷土壤在不同铜离子浓度条件下,pH 对铝释放的影响。结果显示,随着加入铜离子浓度的增加,离子交换作用而引起的可溶性铝也随之增加,相同pH 条件下,可溶性铝的解吸量依次为砖红壤>红壤>黄棕壤>棕壤,恒电荷土壤中铜离子浓度变化对铝释放的影响较可变电荷土壤更大,当pH大于3.6（恒电荷土壤）或pH 大于4.0（可变电荷土壤）时,溶液中可溶性铝的含量几乎可以忽略不计。因此在所研究的铜离子浓度范围内,引起可溶性铝离子量变化的主导因素应该是体系pH 值的变化而非铜离子的吸附。