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121.
This paper investigates the interfacial structure in hot-wall CVD TiN/κ-Al2O3 multilayer coatings using both HREM and DFT modeling. Two multilayers with different thicknesses of the TiN layers (50 and 600 nm) separating the κ-Al2O3 layers are analyzed. The general microstructure of the two multilayers is relatively similar. The TiN layer in the thicker TiN/κ-Al2O3 coating is thick enough to be several TiN grains high. This means that epitaxial columns, which are often found in the thinner TiN/κ-Al2O3 coatings, are not present. However, the orientation relationships at the TiN/κ-Al2O3 interfaces are the same in both multilayers. The HREM investigations show that κ-Al2O3 (001) planes can grow directly on flat (111) TiN faces, without any other phases or detectable amounts of impurities, such as sulphur, present. Where the TiN layers are more curved, γ-Al2O3 can be grown, at least partly stabilized by the cube-on-cube orientation relationship between γ-Al2O3 and the underlying TiN. The DFT calculations show very similar adsorption strengths for an O monolayer positioned on Ti-terminated TiC(111) and TiN(111) surfaces, with preferred adsorption in the fcc site. O adsorption on N-terminated TiN(111) is much weaker, with preferred adsorption in the top site. Calculated elastic-energy contributions yield a higher stability for κ-Al2O3 on TiN(111) than on TiC(111) and a higher stability for κ-Al2O3 than for α-Al2O3 on both TiC and TiN. This indicates that the observed higher stability of κ-Al2O3 on TiC(111) than on TiN(111) is not due to the lattice mismatch, while the preferred epitaxial growth of κ-Al2O3 over α-Al2O3 can be partly attributed to the mismatch. 相似文献
122.
The technology of cold pressure welding was adopted to achieve the bonding of Al/Cu(limited soluble and forming compounds),Ag/Ni(hardly mutual soluble),and the relative state of interface was tested by HREM.The results indicate that stable interface is always corresponding to the low interfacial energy value;the stable interface is not coherent but partly-coherent because of the twisting of grain boundary caused by pressure,meanwhile existing dislocation.Namely,the interfacial match and other states under the condition of cold pressure welding are different from the situation that under the condition of thermal action.Moreover,theoretical analyses and calculation on the base of thermodynamics,crystallogeny ,solid physics etc,were discussed. 相似文献
123.
J. R. Tarpani W. W. Bose Filho D. Spinelli 《Journal of Materials Engineering and Performance》2002,11(5):563-570
The elastic-plastic fracture toughness and crack extension behavior under the quasi-static loading regimen of several thermally
embrittled conditions of a nuclear reactor pressure vessel (RPV) steel were assessed on the basis of microstructural parameters.
It was discovered that the bainite packet size is the fracture properties controlling parameter of single-phase quenched and
tempered microstructures. Results were found in close agreement to those obtained in a parallel study with dual-phase annealed
microstructures derived from the same low alloy steel. Similarly, it was concluded that a Hall-Petch type relationship correlates
J-fracture mechanics criteria to the grain size. 相似文献
124.
125.
TiAl 合金中的γ→α析出转变行为 总被引:1,自引:2,他引:1
研究了Ti-48Al和Ti-48Al—0.8B合金中的γ→α析出转变,分析了α析出相的生长形态、晶体学特征、生长动力学及α/γ相界面结构。结果显示α相从γ相中析出有两种方式:一种是从γ晶粒内沿{111},晶面以片状形貌析出,且α相与γ基体保持共格位向关系;另一种则是在γ晶界上通过不连续析出转变,以不规则的块状形貌析出,并向着晶界一侧与之无位向关系的γ晶粒内生长。添加0.8%(摩尔分数)B能显著降低γ晶粒内片状α析出相的形核率,并抑制α相生长。HREM分析表明:片状α相是在γ相的堆垛层错上形核,并通过“台阶-凸起-扭折”机制生长;α/γ相界面上复杂层错的存在及台阶形核率低是片状α相沿厚度方向生长缓慢的主要原因。 相似文献
126.
以定量分析钢筋与混凝土粘结滑移关系为目标,利用RCXFEHohai-P扩展有限元程序,计算采用不同粘结滑移公式时钢筋混凝土简支梁的最大裂缝宽度。结果表明,计算所得最大裂缝宽度各不相同,且都与《混凝土结构设计规范》(GB 50010—2010)所列最大裂缝宽度公式计算值存在差别。为此,基于GA-BP神经遗传网络,以规范最大裂缝宽度公式计算值为预测目标,反演得到适用于扩展有限元裂缝计算的粘结滑移公式,算例表明该公式能满足扩展有限元裂缝宽度计算要求。研究成果对提高扩展有限元裂缝分析的准确性具有一定的参考价值。 相似文献
127.
《Information and Software Technology》2014,56(1):40-53
ContextThe dependencies between individual requirements have an important influence on software engineering activities e.g., project planning, architecture design, and change impact analysis. Although dozens of requirement dependency types were suggested in the literature from different points of interest, there still lacks an evaluation of the applicability of these dependency types in requirements engineering.ObjectiveUnderstanding the effect of these requirement dependencies to software engineering activities is useful but not trivial. In this study, we aimed to first investigate whether the existing dependency types are useful in practise, in particular for change propagation analysis, and then suggest improvements for dependency classification and definition.MethodWe conducted a case study that evaluated the usefulness and applicability of two well-known generic dependency models covering 25 dependency types. The case study was conducted in a real-world industry project with three participants who offered different perspectives.ResultsOur initial evaluation found that there exist a number of overlapping and/or ambiguous dependency types among the current models; five dependency types are particularly useful in change propagation analysis; and practitioners with different backgrounds possess various viewpoints on change propagation. To improve the state-of-the-art, a new dependency model is proposed to tackle the problems identified from the case study and the related literature. The new model classifies dependencies into intrinsic and additional dependencies on the top level, and suggests nine dependency types with precise definitions as its initial set.ConclusionsOur case study provides insights into requirement dependencies and their effects on change propagation analysis for both research and practise. The resulting new dependency model needs further evaluation and improvement. 相似文献
128.
2DPCA-SIFT:一种有效的局部特征描述方法 总被引:7,自引:0,他引:7
PCA-SIFT (Principal component analysis—scale invariant feature transform)方法通过对归一化梯度向量进行PCA降维,在保留特征不变性的同时,有效地降低了特征矢量的维数,从而提高了局部特征的匹配速度. 但PCA-SIFT中对本征向量空间的求解非常耗时,极大地限制了PCA-SIFT的灵活性与应用范围. 本文提出采用2DPCA对梯度向量块进行降维的特征描述方法. 该方法相比于PCA-SIFT,可以快速地求解本征空间. 实验结果表明:2DPCA-SIFT在多种图像变换匹配和图像检索实验中可以实现与PCA-SIFT相当的性能,并且从计算效率上看,2DPCA-SIFT具有更好的扩展性. 相似文献
129.
130.