不同桥形微结构换能元的仿真设计与实验研究

微结构换能元是微机电系统(Micro Electro?Mechanical Systems,MEMS)火工品的关键器件,其桥区微结构设计对MEMS火工品的输出性能和能量利用率具有显著影响。为完善MEMS火工品微结构换能元设计理论,设计制作了8种不同桥形微结构换能元,采用仿真研究与红外测试等手段进行微结构换能元桥形结构优选与微结构效应研究,获得了V?50和L?1两种优选桥形结构换能元,揭示了不同桥形结构对换能元输出性能的影响规律,其中V?50桥形微结构换能元平均发火电压达到了100μF/3.5 V,能量利用率为46.6%。

薄膜微结构换能元温度测量技术研究

为了适应火工品微型化、集成化和智能化等发展趋势,薄膜微结构换能元的引发温度测试已成为一项亟需解决的关键问题。采用MEMS技术将薄膜铂电阻和薄膜微结构换能元集成在氮化硅基底上,利用原子力显微镜等设备对薄膜铂电阻的几何尺寸进行了表征,通过实验测量了薄膜微结构换能元在不同直流激励下铂电阻的阻值变化,从而得到了薄膜微结构换能元的温度响应曲线。此外,测得斯蒂芬酸铅的点火温度平均为318℃,与理论值330~350℃接近,验证了将薄膜铂电阻与薄膜微结构换能元集成于一体测量微小尺寸条件下发火温度的可行性与有效性。

预报纤维增强复合材料有效热导率的随机微结构胞元模型

发展了能预报复合材料有效性质的随机微结构胞元模型以预测单向纤维增强复合材料横向热导率。研究了能反映宏观有效性质的模型最小化问题,探讨了微结构影响宏观有效热传导性能的机制。结果表明:通过对模型指定周期边界条件并且以多个合适的小规模模型计算的平均值取代大模型计算,可大大改进收敛性并提高计算效率,从10×10个到30×30个子胞的模型,所得有效热导率计算结果的最大相对变化量仅为0.6%。不同纤维排列引起热流穿过热阻大的基体的路径长度改变,造成有效热导率不同;纤维热导率远大于基体热导率时,纤维随机分布造成纤维偏聚,部分纤维接触形成'热流通道',使得有效热导率增大,揭示了某一体积分数下有效热导率急剧增加是由'热流通道'贯通引起。与实验结果的比较说明了微结构随机性研究的必要性和本文工作的实用价值。

尺度关联的微结构构型与排布的材料/结构动力学设计

考虑微观尺度和宏观尺度的关联,将微结构胞元设计和多尺度均匀化设计结合,建立了由相同尺寸和内部构型的微结构胞元组成的复合材料结构的材料/结构一体化动力学优化设计方法,给出了相应的算例。方法中引入了微观和宏观两个尺度上的独立密度变量,采用材料属性的合理近似模型对密度进行惩罚,利用有限元超单元技术建立材料与结构的联系。基于算例获得了超单元尺寸与微观、宏观材料用量对结构拓扑构型的影响规律。将算例结果与已有方法的结果比较,表明本文方法具有合理有效性,可作为对轻质结构进行动力学设计的一种新方法。

自愈合碳化硅陶瓷基复合材料研究及应用进展

为了满足高推重比航空发动机长时热力氧化环境的使用需求,连续纤维增韧碳化硅陶瓷基复合材料正朝自愈合方向发展。本文介绍自愈合碳化硅陶瓷基复合材料的微结构与性能,自愈合与强韧化机理,制造方法和工艺特点及其在航空发动机热端部件的应用情况,表明多元多层微结构形成了“层层设防,就地消灭”的氧化防御体系,是复合材料实现自愈合与强韧化的关键。自愈合碳化硅陶瓷基复合材料能够满足发动机高温服役环境要求,显著降低发动机的结构重量,从而有效提高发动机的推重比。

Morphology and chemical composition of γ/γ' phases in Re-containing Ni-based single crystal superalloy during two-step aging

The γ/γ＇ microstructure of a Re-containing Ni-based single crystal super alloy after a two-step aging was studied using scanning electron microscopy （SEM）,transmission electron microscopy （TEM） and scanning transmission electron microscopy （STEM）.The crystals were grown by the floating zone （FZ） method.Both cuboidal and spherical γ＇ precipitates were formed after a two-step aging.The size of the cuboidal γ＇ phases first increased and then decreased with the extension of the second-step aging time.Re,Co and Cr strongly concentrated in the γ phase whereas Ni and Al enriched in the γ＇ phase.Thermodynamic calculation by JMatPro was performed to explain the experimental observations.

Local structure of calcium silicate melts from classical molecular dynamics simulation and a newly constructed thermodynamic model

The distributions of local structural units of calcium silicate melts were quantified by means of classical molecular dynamics simulation and a newly constructed structural thermodynamic model. The distribution of five kinds of Si-O tetrahedra Qi from these two methods was compared with each other and also with the experimental Raman spectra, an excellent agreement was achieved. These not only displayed the panorama distribution of microstructural units in the whole composition range, but also proved that the thermodynamic model is suitable for the utilization as the subsequent application model of spectral experiments for the thermodynamic calculation. Meanwhile, the five refined regions mastered by different disproportionating reactions were obtained. Finally, the distributions of two kinds of connections between Qi were obtained, denoted as Qi-Ca-Qj and Qi-[Ob]-Qj, from the thermodynamic model, and a theoretical verification was given that the dominant connections for any composition are equivalent connections.

Effects of substituting La with M(M=Sm, Nd, Pr) on electrochemical hydrogen storage characteristics of A_2B_7-type electrode alloys

The partial substitution of M （M=Sm, Nd, Pr） for La was performed in order to ameliorate the electrochemical hydrogen storage performance of RE–Mg–Ni-based A2B7-type electrode alloys. The La0.8–xMxMg0.2Ni3.35Al0.1Si0.05 （M=Sm, Nd, Pr;x=0-0.4） electrode alloys were fabricated by casting and annealing and their microstructures were characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The major phases （La, Mg）2Ni7 with the hexagonal Ce2Ni7-type structure and LaNi5 with the hexagonal CaCu5-type structure make up the basic microstructure of the experimental alloys. The discharge capacities of the as-cast and annealed alloys all gain their maximum values with the M （M=Sm, Nd, Pr） content varying. The electrochemical cycle stability of the as-cast and annealed alloys clearly rises with the M （M=Sm, Nd, Pr） content growing. Furthermore, the electrochemical kinetics of the alloys, including the high rate discharge ability, charge transfer rate, limiting current density and hydrogen diffusion coefficient, all present a increase trend at first and then decrease with the rising of M （M=Sm, Nd, Pr） content.

Comparative Studies on the Fine Structure and Elemental Composition of Envelopes of Trachelomonas and Strombomonas (Euglenophyta)

Fine structure and elemental composition of envelopes of 10 taxa of Trachelomonas and Strombomonas from natural freshwater bodies in China were studied and phylogeny of both genera were discussed. The results indicate that iron (Fe) and silicon (Si) are the primary mineral elements of the envelopes. Composition of mineral elements was uncorrelated with envelope color, however, it was highly correlated with the microarchitecture of the envelopes. Content of Si was higher than that of Fe in all species of Strombomonas and some species of Trachelomonas with rough surface. In most species of Trachelomonas, especially those with dense and smoothy surface, content of Fe was higher than that of Si. Based on the above results, we propose to assign those species of Strombomonas into Trachelomonas and consider them as a group of the latter. These species were the most primitive among the group with envelopes in Euglenaceae.

Beryllium-distribution in metallic glass matrix composite containing beryllium

The morphologies, sizes, compositions and volume fractions of dendritic phases in in situ Ti-based metallic glass matrix composites （MGMCs） containing beryllium （Be） with the nominal composition of Tia7Zr19Cu5V12Be17 （mole fraction, %） were investigated using XRD, SEM, EBSD, TEM, EDS and three-dimensional reconstruction method. Moreover, visualized at the nanoscale, Be distribution is confirmed to be only present in the matrix using scanning transmission electron microscopy-electron energy loss spectroscopy （STEM-EELS）. Based on these findings, it has been obtained that the accurate chemical compositions are Wi28.3Zr19.7Cu8V6.4Be37.6 （mole fraction, %） for glass matrix and Wi62.nZr18.aCu2.6V16.6 （mole fraction, %） for the dendritic phases, and the volume fractions are 38.5% and 61.5%, respectively. It is believed that the results are of particular importance for the designing of Be-containing MGMCs.

硬质涂层的研究热点及面临问题

硬质涂层的制备及改性是当今涂层领域的研究热点之一,随着科学技术的迅速发展及工业要求的不断提高,对硬质涂层材料、性能及其制备技术则提出了更高的要求。本文主要从硬质涂层制备、组元微结构设计及其强化/退化机理、高性能硬质涂层三方面展开,介绍了硬质涂层领域的一些热点研究方向及其目前存在的问题。主要包括以下内容:发展新的沉积系统和涂层制备新技术,实现一些硬质涂层的低温沉积、低压沉积和高速率沉积,以及亚稳相的制备等;基于对Veprek制备的nc-TmN/a-Si3N4纳米复合涂层结构模型和理论解释的质疑,提出纳米晶/非晶复合涂层的研究重点;对比了氧元素在不同的涂层体系中所扮演的角色及其作用机制;总结了低应力厚硬质涂层的结构设计方法、对应机理及存在问题;归纳了一些高性能硬质涂层所需要具备的性能特点及实现方法,如高韧性、高抗裂纹扩展能力涂层,高热稳定性、抗氧化性涂层,超硬耐磨自润滑硼化物涂层。

Constitutive model of rock based on microstructures simulation

The constitutive model of rock can be built by mechanics elements because there are many kinds of damages in rock under varied loads.It is resumed that rock contains many microstructures and a structure of Bingham.The microstructure consists of two embranchments that are the unit of a spring and a gliding slice in series and the unit of a spring and a cementation bar in series,the two units connect each other in parallel.These microstructures are arranged disorderly or in the order of a certain state.A certain distribution of microstructures represents one type of rock.Two kinds of rock's constitutive relationship were deduced by using the model.One is the model in which many parallel microstructures and a structure of Bingham connect in series.And it is used to homogeneous rock.The other is the model in which many microstructures and a structure of Bingham connect in series.And it is used to the rock with much crack or microcrack in a certain direction.The two kinds of constitutive relationship were verified by the studied cases.The constitutive model of rock built by using mechanics elements is verified to be reasonable.Moreover,different types of rocks may be described with mechanics elements with different distributions.

Microstructure and mechanical behavior of Ti/Cu/Ti laminated composites produced by corrugated and flat rolling

Ti/Cu/Ti laminated composites were fabricated by corrugated rolling(CR) and flat rolling(FR) method.Microstructure and mechanical properties of CR and FR laminated composites were investigated by scanning electron microscopy, numerical simulation methods, peel and tensile examinations. The effect of CR and FR was comparatively analyzed. The results showed that the CR and FR laminated composites exhibited different effective plastic strain distributions of the Ti layer and Cu layer at the interface. The recrystallization texture, prismatic texture and pyramidal texture were developed in the Ti layer by CR, while the R-Goss texture and shear texture were developed in the Cu layer by CR. The typical deformation texture components were developed in the Ti layer and Cu layer of FR laminated composites. The CR laminated composites had higher bond strength, tensile strength and ductility.

Influence of cerium on microstructures and mechanical properties of Al-Zn-Mg-Cu alloys

Effect of element cerium （Ce） on microstructure and mechanical properties of A1-Zn-Mg-Cu alloys has been investigated by transmission electron microscopy （TEM）, scanning electron microscopy （SEM）, differential scanning calorimetry （DSC） and hardness test. The results show that addition of Ce can remarkably refine the as-cast grains and eutectic microstructure. A transformation from Mg（Zn,Cu,A1）2 phase to A12CuMg phase is observed during homogenization. Furthermore, the Ce addition introduces changes in the precipitation process and consequently in the age-hardening behavior of the alloy. Microstructural measurements reveal that the addition of Ce promotes the precipitation of η＇ phase, but it also partly retards the precipitation of GP zones. The density of precipitates decreases in a certain degree and rod-like η＇ precipitates increase when Ce content is from 0.2% to 0.4% （mass fraction）.

Microstructures and properties of WC-20Co-1Y_2O_3 cemented carbide by hot-press and liquid phase sintering

Ultrafine tungsten carbide and fine cobalt as well as nano yttrium oxide powders were used as the raw materials. The effects of hot-press below the eutectic temperature and conventional liquid phase sintering on the structures and properties of WC-20Co-1Y2O3 cemented carbide were studied. It is shown that hot-pressed alloy has the character of isotropic properties and microstructure with homogeneous and ultrafine WC grains. However, the ultrafine and fully-densified structure is developed at the cost of the presence of large amount of cobalt-lake （unevenly distributed binder phase）, and thus lower strength. Yttrium oxide in the alloy cannot play the role of grain growth inhibitor fully when cemented carbide with high content of cobalt and ultrafine raw materials is sintered at high liquid phase sintering temperature. Peculiar platelet-enhanced bi-model structure is formed in WC-20Co-1Y2O3 cemented carbide by conventional liquid phase sintering, which points out that yttrium oxide in the alloy facilitates the formation of plate-like WC grain.

Effect of element Gd on phase constituent and mechanical property of Mg-5Sn-1Ca alloy

The Mg-5Sn-1Ca-xGd (x=0, 1) alloys were chosen to investigate the change in solidification paths, phase formation and mechanical properties. The microstructure of as-cast Mg-5Sn-1Ca alloy is composed of α-Mg, Mg2Sn and CaMgSn phases. With the addition of Gd, the formation of the Mg2Sn phase is impeded and the CaMgSn phase is refined, whereas the ultimate tensile strength and elongation decrease. The possible reasons for the variation in microstructure and mechanical properties were discussed.

Influence of minor Sc additions on grain refinement and microstructure characteristics of a high Zn-containing Al-Zn-Mg-Cu-Zr alloy

In the present work, scandium elements with a series of contents(0.06 wt.%, 0.10 wt.%, 0.14 wt.%,0.17 wt.%, 0.20 wt.% and 0.25 wt.%) were added in a high Zn-containing Al-Zn-Mg-Cu-Zr alloy and the corresponding as-cast microstructure characteristics including grains and phases were thoroughly investigated. The results indicated that fine grain boundaries existed in these alloys and fine MgZn2phases discontinuously distributed on them. Besides,AlZnMgCu eutectic phases and Sc, Zr-containing phases with flocculent morphology were observed. As scandium contents vary from 0.06 wt.% to 0.17 wt.%, the average grain size continuously decreased and its equiaxial characteristics were strengthened. Meanwhile, the content of AlZnMgCu eutectic phase showed a decrease trend. When scandium contents were 0.20 wt.% and 0.25 wt.%, no further enhancement on grain refinement was observed, so as to the reduction of AlZnMgCu eutectic phase content. Besides, Sc, Zr-containing phases with blocky morphology were observed and the alloy with a scandium content of 0.25 wt.% possessed a larger amount of blocky Sc, Zr-containing phase than the alloy with a scandium content of 0.20 wt.%. Grain refinement and reduction of AlZnMgCu eutectic phase content associated with scandium addition were discussed.

Effect of CuO and SnO_(2) particle size on hot extrusion deformation of AgCuOSnO_(2):Finite element simulation and experimental study

The finite element model is established according to the experimental results,and then the experimental results are verified by simulation calculation.In terms of the combination of finite element analysis and experiment,the effect of particle size of CuO and SnO_(2) on the stress,strain and microstructure of AgCuOSnO_(2) composite during hot extrusion was studied.The results illustrate that with the decrease of particle size,the dispersion of the second phase increases gradually,while the possibility of“tail shrinkage”of the billet decreases continuously;cubic CuO will evolve to fibrosis,and the degree of fibrosis will increase with the decrease of the particle size and ring clusters.Specifically,the degree of fibrosis at the middle end of the billet is higher than that at the front end,the degree of fibrosis at the front end is higher than that at the back end,and the degree of fibrosis on the surface is higher than that in the core;part of CuO fibers will bend,and the degree of buckling strength is positively correlated with the size of particles and their annular clusters.Additionally,there is fiber CuO in the front and back end of the billet that are inconsistent with the extrusion direction,and the degree of difference was negatively correlated with the particle size.

A Comprehensive Comparison of the Analytical and Numerical Prediction of the Thermal History and Solidification Microstructure of Inconel 718 Products Made by Laser Powder-Bed Fusion

The finite-element （FE） model and the Rosenthal equation are used to study the thermal and microstructural phenomena in the laser powder-bed fusion of lnconel 718. A primary aim is to comprehend the advantages and disadvantages of the Rosenthal equation （which provides an analytical alternative to FE analysis）, and to investigate the influence of underlying assumptions on estimated results. Various physical characteristics are compared among the FE model, Rosenthal equation, and experiments. The predicted melt pool shapes compared with reported experimental results from the literature show that both the FE model and the analytical （Rosenthal） equation provide a reasonably accurate estimation. At high heat input, under conditions leading to keyholing, the reported melt width is narrower than predicted by the analytical equation. Moreover, a sensitivity analysis based on choices of the absorptivity is performed, which shows that the Rosenthal approach is more sensitive to absorptivity, compared with the FE approach. The primary reason could be the effect of radiative and convective losses, which are assumed to be negligible in the Rosenthal equation. In addition, both methods predict a columnar solidification microstructure, which agrees well with experimental reports, and the primary dendrite arm spacing （PDAS） predicted with the two approaches is comparable with measurements.

Process parameter effects on microstructure and mechanical properties of tubes processed via friction assisted tube straining method

This paper investigates process parameter effects on microstructure and mechanical properties of the tubes processed via recently developed friction assisted tube straining(FATS)method.For this purpose,design of experiment was used to arrange finite element analyses and experimental tests.Numerical and experimental tests were executed by changing rotary speed,feed rate and die angle.Taguchi design results show that increasing feed rate and decreasing rotary speed enhance Zener-Hollomon(Z)parameter and decrease average grain size,while die angle has no considerable effect.Increasing Z value reduces grain size and enhances flow stress of the processed samples,while the experiment with the highest Z value refines initial microstructure from 40 to 8μm and increases flow stress by 5 times.