Joining of Si3N4 to Si3N4 using a AuPd(Co,Ni)–V filler alloy and the interfacial reactions

Au38.0–Pd28.0–Co18.0–Ni7.0–V9.0 (in wt%) alloy was designed as a filler for joining Si₃N₄. The filler alloy showed a contact angle of 77.2° on Si₃N₄ ceramic at 1473 K. The Si₃N₄/Si₃N₄ joint brazed with the rapidly-solidified filler foils at 1443 K for 10 min exhibits an average three-point bend strength of 320.7 MPa at room temperature and the strength values are 217.9 MPa and 102.9 MPa at 1073 K and 1173 K respectively. The interfacial reaction products were composed of V₂N and Pd₂Si, and the elements Co and Ni in the brazing alloy did not participate in the interfacial reactions. The coarse-network-like distribution of refractory Pd₂Si compound within the Au–Pd–Co–Ni alloy matrix throughout the joint contributes to the stable high-temperature joint strengths.     

有机硅密封剂高温力学性能研究

在温度25~250℃对3类硫化体系的5种有机硅密封剂的拉伸强度、180o剥离强度和剪切强度的研究表明:随着温度的升高,5种有机硅密封剂的拉伸强度、180o剥离强度和剪切强度均不断下降,其中拉伸强度和剪切强度降低的速率递减。有机硅密封剂的高温性能变化与硫化体系类型密切相关,脱氢硫化体系HM321密封剂在25~150℃拉伸强度、剪切强度和180o剥离强度均最高,但在25~250℃拉伸强度、剪切强度和180o剥离强度保持率均最低。脱氨硫化体系XY-602S有机硅胶粘剂在232~250℃的拉伸强度和剪切强度最高,25~250℃的拉伸强度保持率也最高。     

Microstructure evolution in abrasion-induced surface layer on an Al–Zn–Mg–Cu alloy

An altered surface layer forms on an Al–Zn–Mg–Cu alloy during surface preparation by abrasion with grinding paper. Strain-induced dissolution of η′/η precipitates and formation of nano-sized subgrains were observed in the surface layer with thickness of several hundred nanometers. The segregation of solute elements along dislocations and subgrain boundaries and the precipitation of Al₂Cu phase at the sub-boundaries and the free surface were related to enhanced diffusion accelerated by deformation-induced vacancies, dislocations and subgrain boundaries. The microstructure evolution in this layer is mainly attributed to the shear strain and is modified by temperature rise during surface abrasion. The unique surface microstructural changes produced by abrasion might alter the surface properties.     

Study on Cure Behavior of a Model Epoxy System by Means of TTT Diagram

Duetotheirhighstrength,modulusandfracture toughnessaswellasgoodadhesionandthermalre sistance[1],epoxyresinsasmatricesarewidelyused inaeronautics,astronautics,transportation,sports andotherindustry.Standardepoxyresinsareusually basedonDGEBA(diglycidyletherofbisphenolA),whichneedsactivehydrogenorotheractivegroupsto opentwoepoxyrings.Four functionalepoxylike TGMDA(tetraglycidylmethylenedianiline)isoften usedforhigh performanceepoxymatrixcomposites becauseofitsrelativelyhighercross linkingdens…     

织物预成型体厚度方向渗透特性研究

以达西定律为基础,研究了不同类型织物的织物层数、定型剂质量分数以及铺层角度对织物预成型体厚度方向上渗透性能的影响.实验结果表明,在一定的定型剂质量分数下,测试流体在垂直方向上的流动基本为稳态流动,大体受Darcy定律控制.随着织物层数的增加,流体流速减小,预成型体厚度方向渗透率逐渐增加.随定型剂质量分数的增加,厚度方向渗透率表现出先增大而后又减小的趋势,而且织物的铺层角度对预成型织物厚度方向渗透率也具有较大影响.     

用纯金属Ni作中间层扩散连接铝基复合材料

采用纯金属Ni作中间层扩散连接氧化铝颗粒增强铝基复合材料(Al2O3P/6061Al),探究了连接温度和保温时间对接头显微结构与力学性能的影响.结果表明,连接温度610～620℃时,连接区主要由Al3Ni和Ni在Al中固溶体组成,Al3Ni含量随连接温度升高、保温时间延长而减少;连接温度630℃时,连接区主要由Al2O3颗粒和Ni在Al中固溶体组成,Al2O3颗粒偏聚于接头中心.连接温度620℃、保温时间5～120min条件下,接头抗剪强度68～93MPa,断裂于连接区与母材界面;连接温度630℃、保温时间5～120min条件下,接头抗剪强度93～97MPa,断裂于增强相偏聚区.     

有机玻璃在紫外光下老化机理的研究

在紫外光（50℃，313nm波长）条件下对有机玻璃进行了约70d（天）的人工加速老化试验，然后对不同老化时间的有机玻璃试样进行了力学性能测试，并进一步利用凝胶渗透色谱法、示差扫描量热法等手段，分析了老化前后的有机玻璃试样的结构和组成差异，结合老化前后有机玻璃力学性能的变化，定性的揭示了有机玻璃在紫外光条件下的老化规律和老化机理。     

SMALL CRACK GROWTH AND FATIGUE LIFE PREDICTIONS FOR HIGH-STRENGTH ALUMINIUM ALLOYS: PART I—EXPERIMENTAL AND FRACTURE MECHANICS ANALYSIS

The small crack effect was investigated in two high-strength aluminium alloys: 7075-T6 bare and LC9cs clad alloy. Both experimental and analytical investigations were conducted to study crack initiation and growth of small cracks. In the experimental program, fatigue tests, small crack and large crack tests were conducted under constant amplitude and Mini-TWIST spectrum loading conditions. A pronounced small crack effect was observed in both materials, especially for the negative stress ratios. For all loading conditions, most of the fatigue life of the SENT specimens was shown to be crack propagation from initial material defects or from the cladding layer. In the analysis program, three-dimensional finite element and weight function methods were used to determine stress intensity factors and to develop SIF equations for surface and corner cracks at the notch in the SENT specimens. A plasticity-induced crack-closure model was used to correlate small and large crack data, and to make fatigue life predictions. Predicted crack-growth rates and fatigue lives agreed well with experiments. A total fatigue life prediction method for the aluminium alloys was developed and demonstrated using the crack-closure model.     

Initial Magnetization Curve and Hardening Mechanism in the Nanocomposite Nd8Fe85Nb1B6 Ribbon

The melt-spun Nd8Fe85Nb1B6 ribbon was prepared by the single roller method with the tangential speed of 20 m/s. A mixture of Nd2Fe14B and α-Fe phases with the average crystalline grain size of about 20 nm was found to exist in the as-quenched ribbons. The initial magnetization curve of the nanocomposite Nd8Fe85Nb1B6 ribbon can be divided into four sections by the inflection points on it. The magnetically hardening mechanism corresponding to each section was investigated. The initial susceptibility of the Nd8Fe85Nb1B6 ribbon is higher than that of the Nd15Fe85B9 powder, which may be attributed to the reversible magnetization rotation in the central region not influenced by the exchange-coupling effect within the α-Fe grains.The above-mentioned magnetization rotation leads to the formation of equilibrium 180 deg. domain walls at the boundaries of the α-Fe grains. With the increase of applied field, these domain walls are compressed reversibly towards the Nd2Fe14B grains and eventually invade into them.The irreversible movement of the domain walls in the Nd2Fe14B grains accounts for the steepest growth of magnetization with the applied field. Finally, the magnetically inhomogeneous “core regions” are formed in the Nd2Fe14B grains, and the magnetization rotation in these“core regions”indicates the end of the whole initial saturation process.     

高温合金中钨元素的看谱分析技术应用研究

对高温合金中钨元素的看谱分析技术进行了研究,摄制并标定了高温合金中钨元素的彩色图谱,制定了半定量分析测定用强度标。研究结果可用于高温合金中钨元素的定性和半定量分析及材料牌号鉴别。