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121.
闫五柱 《稀有金属材料与工程》2016,45(9):2303-2306
为了探索用压痕法确定晶体学蠕变应力指数的可行性,采用晶体塑性理论模型对不同取向镍基单晶合金压痕蠕变行为进行了有限元模拟。研究表明,晶体学对称性会导致压痕表面应力呈现特定的对称性;晶体取向对压痕蠕变深度及其扩展速率具有显著的影响。通过开展不同载荷下的压痕蠕变模拟,获得相应的稳态压痕深度扩展速率,再通过线性回归的方法可有效获得晶体学蠕变应力指数。本文提出的确定蠕变应力指数的方法不受晶体取向的影响,有望应用于各向异性高温合金蠕变性能评估。 相似文献
122.
化学镀镍内应力的研究 总被引:3,自引:0,他引:3
用于非金属电镀、电铸、化学镀、化学铸的现行许多化学镀镍工艺,总是在零件尖端部位发生崩裂,在镜面光洁的地方易起泡,这种难题至今未得到很好解决,这大大限制了化学镀镍的应用.针对这种情况,采用正交实验方法开发出一个低温、低内应力化学镀镍工艺,初步探讨了沉积层内应力与各工艺参数之间的关系,以及作为添加剂的糖精在化学沉积层中的作用机理,并对内应力和结合力的关系作了简介.实践证明了该工艺在短时间内能于多种复杂形状或镜面光亮的非金属表面上获得完整的化学镍沉积层. 相似文献
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The effect of directional solidification and heat treatments on the microstructure and mechanical properties of intermetallic Ni–21.29Al–7.04Cr–1.46Ta–0.64Mo–0.57Zr (at.%) alloy was studied. Increasing growth rate is found to decrease primary dendrite arm spacing and to increase volume fraction of β(NiAl)-based dendrites and low melting point γ′(Ni3Al)/Ni5Zr eutectic. Room-temperature tensile yield strength and ultimate tensile strength increase and plastic elongation to fracture decreases with the increasing growth rate. Two types of heat treatments of directionally solidified (DS) specimens including two-step ageing at temperatures of 1273 and 1123 K and two-step solution annealing at 1373 and 1493 K were performed. Ageing at 1273 and 1123 K decreases volume fractions of the dendrites and eutectic regions and leads to a coarsening of spherical -Cr and needle-like γ′ precipitates within the β-phase. Annealing at 1373 K for 100 h is shown to be sufficiently long to completely dissolve the eutectic regions. Compressive yield strength increases with increasing temperature reaching a peak value at about 1023 K and then decreases at higher temperatures. Minimum creep rate is found to depend strongly on the applied stress and temperature according to a power law. The power law stress exponent n is determined to be 5.1 and apparent activation for creep Qa is measured to be 326 kJ/mol. 相似文献
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To obtain a durable Ni coating with excellent adhesion strength on an AZ91D Mg alloy, a pretreatment was performed with a small amount of Cu2+ ions added to the activation bath used in the pretreatment prior to the plating process. In the pretreatment activation process, a high density Cu layer was deposited on both the α-phase and β-phase areas of the substrate accompanied with Mg dissolution. The Cu deposit acted as nucleation seeds for the Zn deposition in the following zincate process which provided a uniform and dense Zn layer almost completely covering the substrate. Then a thin Cu layer was electroplated on this zincated substrate as an undercoating for the succeeding electroplating with Ni. Cross-sectional scanning electron microscopy observations showed that the Cu deposited by the pretreatment enabled the deposition of a protective Ni layer with few defects. This structure also contributed to the improvement of adhesion strength and corrosion resistance as compared with the non-Cu added sample. 相似文献
128.
J. Yamamatsu N. Kawano T. Arashi A. Sato Y. Nakano T. Nomura 《Journal of power sources》1996,60(2):199-203
The reliability of multilayer ceramic capacitors (MLCCs) with Ni internal electrodes has been studied trom the viewpoint of partial oxygen pressure (PO2) during firing. It is shown that the load-life time of the insulation resistance (1R) was prolonged by firing under low Po2 annealing after firing, and the addition of dopants. It is also shown that the generation of oxygen vacancies led to the degradation of IR. Annealing treatment for the oxidation of the dielectric body accelerates the dielectric aging of MLCCs. It is found that the appropriate control of the PO2 during firing can improve the reliability of MLCCs with Ni electrodes to a level as high as that of MLCCs with precious metal electrodes. Thus, we have developed an MLCC with Ni electrodes that features high reliability and a large capacitance of 10 μF for the Y5V characteristic and 4.7 μF for the X7R characteristic, both in the case of the C3216 (3.2 mm × 1.6 mm × 1.4 mm) form. 相似文献
129.
针对芳香硝基化合物的催化选择性加氢反应,开发可替代贵金属催化剂的低成本、高效非贵金属催化剂,对于芳香胺类化合物的绿色生产具有重要意义。利用简易、可规模化的制备方法,以镍—2,5-吡啶二羧酸金属有机框架为前驱体,热解制备了氮掺杂石墨碳包覆镍纳米催化材料(Ni@CN)。采用X射线衍射、扫描电镜、透射电镜、元素分析、N2吸脱附等检测手段对Ni@CN的物化性质进行了表征,并对其催化性能进行了评价。结果表明,Ni@CN可在温和条件下(85℃,1.0 MPa H2)高效加氢含取代官能团的芳香硝基化合物生成对应的芳香胺类化合物。对比试验表明,镍纳米颗粒是Ni@CN的加氢活性中心,而石墨碳壳的存在有利于优先吸附硝基官能团。此外,进一步考察了Ni@CN的循环使用性能以及抗硫化物中毒的特性。 相似文献
130.
Comparative leaching of minerals by sulphuric acid in a Chinese ferruginous nickel laterite ore 总被引:1,自引:0,他引:1
The Yuanjiang nickel laterite ore containing mainly maghemite, goethite and lizardite was leached by sulphuric acid at atmospheric pressure and the residues were characterized using X-ray diffraction and scanning electron microscopy/X-ray energy dispersive spectroscopy. The relationship was discussed between the extraction of nickel, cobalt, iron, magnesium, aluminum, and the dissolution behaviour of the laterite minerals; as well as the extent of congruency of nickel, cobalt and iron extraction. The results show that the solubility of the laterite minerals in sulphuric acid decreases in the following order: lizardite > goethite > maghemite > magnetite ≈ hematite > chromite ≈ ringwoodite. Lizardite dissolved rapidly in 0.6 mol/L sulphuric acid at 60 °C whilst goethite dissolved completely in 2.5 mol/L sulphuric acid at 80 °C. The dissolution of the primary mineral maghemite was slow, but increased with increasing acid concentration and leaching temperature. Magnetite dissolved more slowly than maghemite; and hematite was only dissolved in > 6.2 mol/L sulphuric acid at 105 °C. Chromite and ringwoodite were not dissolved. The leaching behaviour of the laterite minerals may be explained by the bond strength differences of Me–O and the substitution of metal cations in the mineral structure. 相似文献