“Lattice Strain Matching”-Enabled Nanocomposite Design to Harness the Exceptional Mechanical Properties of Nanomaterials in Bulk Forms

Nanosized materials are known to have the ability to withstand ultralarge elastic strains (4–10%) and to have ultrahigh strengths approaching their theoretical limits. However, it is a long-standing challenge to harnessing their exceptional intrinsic mechanical properties in bulk forms. This is commonly known as “the valley of death” in nanocomposite design. In 2013, a breakthrough was made to overcome this challenge by using a martensitic phase transforming matrix to create a composite in which ultralarge elastic lattice strains up to 6.7% are achieved in Nb nanoribbons embedded in it. This breakthrough was enabled by a novel concept of phase transformation assisted lattice strain matching between the uniform ultralarge elastic strains (4–10%) of nanomaterials and the uniform crystallographic lattice distortion strains (4–10%) of the martensitic phase transformation of the matrix. This novel concept has opened new opportunities for developing materials of exceptional mechanical properties or enhanced functional properties that are not possible before. The work in progress in this research over the past six years is reported.     

数值模拟在电解槽集气烟道改造中的应用

针对国内一企业现有电解槽集气烟道存在积灰严重、烟道阻力大、净化能耗高、集气效率低等问题,以该集气烟道为研究对象,利用数值模拟计算软件Workbench对集气烟道改造前后烟道内气流流动情况和集气量进行了仿真计算,得出了改造前后烟道内气流流动分布及集气量结果。结果表明,改造后,在相同的集气负压下,烟道集气量有所增加,各烟道集气口集气量分布均匀。最后以数值模拟计算为依据对集气烟道进行改造,实践证明,改造后集气效率明显提高,改造效果良好。     

预时效对Al-5.2Mg-0.45Cu-2.0Zn合金室温稳定性的影响

本文详细研究了预时效对Al-5.2Mg-0.45Cu-2.0Zn合金时效析出行为的影响。预时效不仅提高了合金的室温稳定性,避免了合金烤漆软化,同时提高了合金的烤漆时效响应速度。合金经T4处理后,再峰时效处理后的组织包括粗大的T-Mg₃₂(AlZn)₄₉相以及针状的S-Al₂MgCu相。然而合金经T4P处理后,再峰时效处理的组织只含有细小而高密度的T-Mg₃₂(AlZn)₄₉相而不包括S-Al₂MgCu相。自然时效后不稳定的原子团簇在180℃时效后会回溶到基体中, 从而抑制了合金的时效析出强化。而预时效后生成的稳定的原子团簇会成为180℃时效的形核点,显著提高了合金的时效响应速度。     

Influence of hexagonal to orthorhombic phase transformation on diffusion-controlled dendrite evolution in directionally solidified Sn–Ni peritectic alloy

The hexagonal to orthorhombic (HO) transformation from β-Ni₃Sn₂ (hexagonal) phase to α’-Ni₃Sn₂ (orthorhombic) phase was confirmed in directionally solidified Sn–Ni peritectic alloys. It is shown that the remelting/resolidification process which is caused by both the temperature gradient zone melting (TGZM) and Gibbs?Thomson (G?T) effects can take place on secondary dendrites. Besides, the intersection angle between the primary dendrite stem and secondary branch (θ) is found to increase from π/3 to π/2 as the solidification proceeds. This is the morphological feature of the HO transformation, which can change the diffusion distance of the remelting/ resolidification process. Thus, a diffusion-based analytical model is established to describe this process through the specific surface area (S_V) of dendrites. The theoretical prediction demonstrates that the remelting/resolidification process is restricted when the HO transformation occurs during peritectic solidification. In addition, the slope of the prediction curves is changed, indicating the variation of the local remelting/resolidification rates.     

Difference Detection Between Two Images for Image Monitoring

In manufacturing industries, images are commonly used for quality control purposes. In such applications, if the quality of the products is good, then their images should be all similar to the image of a good-quality product. Therefore, comparison of images is a fundamental task in image-based quality control. This problem, however, is complicated in the sense that (1) observed images often contain noise, and (2) the related images need to be geometrically matched up first because images of different products could be geometrically mismatched because the relative positions between a camera and different products are often not exactly the same. The first issue requires a statistical method that can remove noise, and the second issue is related to the so-called image registration problem in the image processing literature. In this article, we propose effective methods for detecting difference between two images of products, and our proposed methods can accommodate both noise and geometric mismatch mentioned above. Theoretical results and numerical examples show that they can work effectively in applications.     

Microstructural characteristics of as-forged and β-air-cooled Zr–2.5Nb alloy

Multiple characterization and analysis techniques including electron backscatter diffraction (EBSD), electron channeling contrast (ECC) imaging, transmission electron microscopy (TEM) and microhardness test were jointly employed to investigate microstructural characteristics such as local composition, morphology, grain boundary characteristics and interphase orientation relationship of a forged Zr–2.5Nb alloy before and after β-air-cooling. Results show that the as-forged specimen is composed of equiaxed and lamellar α grains and continuous net-like β-Zr films. After the β-air-cooling, the microstructure of the specimen is featured by basket-weave Widmanstätten structure, in which the inter-α-plate second phases are nanoscale β-Zr. Analyses for crystallographic orientations reveal that the Burgers relationship has been strictly followed during the β→α cooling. Compared to the as-forged specimen, the hardness of the β-air-cooled specimen is higher, which could be attributed to the decreased structural sizes of both α and β phases, and the increased fraction of high angle boundaries as well.     

CVD金刚石表面增透膜的研究进展

CVD金刚石膜因特有的物理化学性质，具有发展成为新一代光学材料的前景。但由于CVD金刚石膜自身局限性导致其理论透过率不到71%，在金刚石膜表面镀制增透膜，通过改变增透膜组成成分、显微组织和晶体结构，可有效地改善CVD金刚石膜自身理论透过率的问题。首先，介绍了CVD金刚石表面镀制单层增透膜增透原理，并总结了物理和化学气相沉积技术制备增透膜的优缺点。然后，重点综述了近年来CVD金刚石表面氮化物、金属氧化物和稀土金属氧化物等增透膜材料的研究进展，详细分析了增透膜制备参数、热处理工艺、衬底表面改性和掺杂工艺对增透膜整体组织和性能影响的规律。其中优化增透膜沉积温度、氧分压和热处理等工艺参数，是通过改变增透膜微观组织形貌以及晶体结构来提高其光学透过性能，而改变衬底表面结构能够通过改变增透膜与基体之间的成键方式来提升界面结合能力，而稀土元素掺杂方式是通过改变增透膜化学组成成分来改善增透膜的光学透过性能，并指出掺杂元素成型机理和影响机制。最后，展望了未来CVD金刚石表面增透膜的发展方向。     

Thermally-induced phase transformations in KNNS-BNKZ lead-free piezoceramics

Promising piezoelectric properties have been reported in potassium sodium niobate-based ceramics by introducing Bi_0.5(Na_0.82K_0.18)_0.5ZrO₃ (BNKZ) into K_0.48Na_0.52Nb_0.95Sb_0.05O₃ (KNNS) solid solutions in order to control the polymorphic phase transformation temperatures. In the present study, synchrotron x-ray powder diffraction (SXPD) was employed in combination with dielectric and ferroelectric measurements in order to clarify the influence of BNKZ on the phase transition temperatures of (1-x)KNNS-(x)BNKZ ceramics (with x = 0 to 0.05). The results, presented in terms of temperature-dependent SXPD patterns, dielectric permittivity and thermal depolarisation characteristics, confirmed that polymorphic phase transformation temperatures all shifted in a systematic manner with increasing BNKZ content. Broadening of the phase transition regions was also observed with increasing BNKZ content, leading to improvements in thermal stability of the ferroelectric properties. Microstructural examination of the KNNS-BNKZ ceramics revealed the presence of core-shell microstructures; this was correlated with the presence of weak shoulders on the diffraction peaks.