氮含量及固溶温度对21-6-9奥氏体不锈钢组织和硬度的影响

为了探讨氮含量及固溶温度对21-6-9不锈钢组织和硬度的影响,分别在950、1000、1050和1100 ℃对3种不同氮含量的热轧态21-6-9不锈钢进行1 h固溶处理,通过光学显微镜观察其组织结构,结合Thermo-Calc热力学计算对试验钢的微观组织进行分析,并对其进行硬度测试。结果表明,0.20%~0.28%N的21-6-9不锈钢热轧后沿轧制方向析出铁素体,且钢中铁素体经950~1100 ℃固溶处理可消除,当N含量达到0.34%时,试验钢中不再出现铁素体。随着固溶处理温度的升高,21-6-9不锈钢的晶粒组织长大,硬度降低。N含量的增加可显著提高固溶态21-6-9不锈钢的硬度,其增加程度随固溶处理温度的升高而减弱。     

巨型水轮发电机剪断销研发与质量控制

为获得设计需要的巨型水轮发电机剪断销的剪切力,得到剪切力波动受控的批量剪断销,通过拉伸试验、冲击试验、硬度试验和剪断销剪切试验等讨论了全尺寸剪断销剪切试验的可行性,分析了剪切试验时正常剪断和非正常剪断的剪断销材料性能差异,探究了剪断销的剪切力质量稳定性控制方法。结果表明:控制剪断销料坯的布氏硬度波动,可实现间接控制剪断销剪切强度的波动;通过试验总结的六步法可达到控制批量剪断销质量和剪切力波动的目的。     

Dense and core-rim structured B4C-TiB2 ceramics with Mo-Co-WC additive

B₄C-TiB₂ ceramics (TiB₂ ranging 5~70 vol%) with Mo-Co-WC as the sintering additive were prepared by spark plasma sintering. In comparison with B₄C-TiB₂ without additive, the enhanced densification was evident in the sintered specimen with Mo-Co-WC additive. Core-rim structured grain was observed around TiB₂ grains. The interface of the rim between TiB₂ and B₄C phases demonstrated different feature: the inner borderline of the rim exhibited a smooth feature, whereas a sharp curved grain boundary was observed between the rim and the B₄C grain. The formation mechanism is discussed: the epitaxial growth of (Ti,Mo,W)B₂ rim around the TiB₂ core may occur as a result of the solid solution and dissolution-precipitation between TiB₂ phase and the sintering additive. It was revealed that the fracture toughness increased as the content of TiB₂ content increased, alongside the decreased hardness. B₄C-30 vol% TiB₂ specimen demonstrated the optimal combination of mechanical properties, reaching Vickers hardness of 24.3 GPa and fracture toughness of 3.33 MPa·m^1/2.     

Structure,mechanical and thermal properties of Y-doped CrAlN coatings

CrAlYN coatings with different Y contents (0, 5 and 12 at.%) were deposited by cathodic arc evaporation to investigate the influence of Y-addition on the structure, mechanical and thermal properties of CrAlN coatings by using X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, thermal gravimetric analysis and nanoindentation. The structural transformation of single phase cubic Cr_0.42Al_0.58N and Cr_0.39Al_0.56Y_0.05N coatings to cubic–wurtzite mixed Cr_0.32Al_0.56Y_0.12N coating leads to a drop in hardness from (30.2±0.7) GPa of Cr_0.42Al_0.58N and (32.0±1.0) GPa of Cr_0.39Al_0.56Y_0.05N to (25.2±0.7) GPa of Cr_0.32Al_0.56Y_0.12N. The incorporation of 5 at.% Y retards the thermal decomposition of CrAlN, verified by the postponed precipitation of w-AlN and N-loss upon annealing. Correspondingly, Cr_0.39Al_0.56Y_0.05N coating consistently exhibits the highest hardness value during thermal annealing. Nevertheless, alloying with Y exerts an adverse effect on the oxidation resistance of CrAlN.     

The influence of brewing method on bioactive compounds residues in spent coffee grounds of different roasting degree and geographical origin

The content of bioactive compounds in spent coffee grounds (SGC) was studied. SGC were obtained from Coffea arabica beans of different roasting degrees (light and dark) and different geographical origins (Nicaragua, Columbia and Mexico) processed using four brewing methods (mocha, filtered, drip and infusion). The highest caffeine and chlorogenic acid contents were determined in filtered spent coffee extracts. All extracts of light roasted spent coffee grounds showed lower browning index levels in comparison to that from dark roasted spent coffee grounds. Generally, the highest content of total polyphenolic compounds and highest antioxidant capacity were determined in extracts prepared in drip. In conclusion, the results obtained in this study indicate that the spent coffee grounds produced of domestic levels, especially those obtained from filter coffeemaker, could be considered as a good source of natural antioxidants.     

Repeated low-velocity impact responses of SiC particle reinforced Al metal-matrix composites

This study aimed to investigate experimentally the repeated low-velocity impact behaviors of SiC reinforced aluminum 6061 metal-matrix composites for different volume fractions and energy levels. In addition, the hardness variations were measured by the Vickers hardness tests from the impacted and impact-free cross-sections of the particle reinforced metal-matrix composites. Low-velocity impact tests were applied to composite samples manufactured by powder metallurgy (in 10, 20, and 30% volume fractions) at two total energy levels (15 and 60 J as single) and in repetitions equal to the sum of these energy levels (5 + 5 + 5 and 20 + 20 + 20 J as repeated). As a result, in increasing the impact number for all volume fractions, the total contact time was shortened and the peak contact force increased, whereas both the permanent central deflection and the absorbed energies reduced. Hence, these variations obtained under repeated impacts (5 + 5 + 5 and 20 + 20 + 20 J) revealed that metal-matrix composites showed a tougher behavior with an increase in the impact numbers from 1st to 3rd, particularly because of the strain hardening effect. Furthermore, an increase in volume fraction from 10 to 30% resulted in an increase in the impact strength under all repeated and single impacts despite changing deformation and damage mechanisms due to increasing the strain hardening effect and particle fractures. The hardness was affected by the volume fraction and increased as the volume fraction increased in both the impacted and impact-free zones. The repeated impact increased the impacted zone hardness more than the single impact for all volume fractions. Additionally, the hardness of the impacted zone under 20 + 20 + 20 J repeated impact was measured as the highest value in the 30% volume fraction. Therefore, metal-matrix composites can behave harder with the strain hardening effect under repeated impacts.     

Chemical Bonding by the Chemical Orthogonal Space of Reactivity

The fashionable Parr–Pearson (PP) atoms-in-molecule/bonding (AIM/AIB) approach for determining the exchanged charge necessary for acquiring an equalized electronegativity within a chemical bond is refined and generalized here by introducing the concepts of chemical power within the chemical orthogonal space (COS) in terms of electronegativity and chemical hardness. Electronegativity and chemical hardness are conceptually orthogonal, since there are opposite tendencies in bonding, i.e., reactivity vs. stability or the HOMO-LUMO middy level vs. the HOMO-LUMO interval (gap). Thus, atoms-in-molecule/bond electronegativity and chemical hardness are provided for in orthogonal space (COS), along with a generalized analytical expression of the exchanged electrons in bonding. Moreover, the present formalism surpasses the earlier Parr–Pearson limitation to the context of hetero-bonding molecules so as to also include the important case of covalent homo-bonding. The connections of the present COS analysis with PP formalism is analytically revealed, while a numerical illustration regarding the patterning and fragmentation of chemical benchmarking bondings is also presented and fundamental open questions are critically discussed.     

Dielectric and mechanical properties of CaCu3Ti3.925(Nb0.5Al0.5)0.075O12 & Al reinforced epoxy-composites (0–3) for embedded capacitor applications

CaCu₃Ti_3.925(Nb_0.5Al_0.5)_0.075O₁₂ [CCTNAO] ceramics were synthesized by microwave assisted solid state reaction technique. CCTNAO ceramics possessed room temperature (RT) dielectric constant (ε_r) ～ 24,173 with tanδ ～0.149 at 1 kHz frequency. Commercially available epoxy-resin, hardener, Al-powder along with CCTNAO powder were used to prepare epoxy based 0–3 composites. Maximum ε_r ～33.37 with tanδ ～0.107 at RT were obtained for 40 vol% CCTNAO loading in epoxy. For x = 0.2 in (1-x)[0.8 Epoxy-0.2 CCTNAO]-x Al Epoxy composites, highest ε_r ～77.6 with tanδ ～ 0.15 at 1 kHz frequency were observed. Increase in ε_r with the increase of Al filler content in composites is attributed to interfacial polarization and cluster formations. Different theoretical models were discussed to explain the dielectric properties of synthesized composites. Experimentally measured values of ε_eff were in close agreement with EMT model (n = 0.13) and Yamada Model (η = 7). An empirical proposed power law ε_eff = ε_m(1+x)ⁿ, with n ～ 10 had a considerable agreement with the experimental results. Vickers hardness test study was carried out to ascertain the mechanical properties of the synthesized composites.     

瞬态闭锁试验在0.13 μm大规模集成电路中引起的潜在损伤

瞬态剂量率辐射试验会引起集成电路发生损伤或失效，其原因至少有两种：闭锁大电流引起的电路内部金属互连熔融；累积电离总剂量引起的氧化层电荷造成阈值电压偏移。本文以一种0.13 μm体硅CMOS处理器为对象，研究了瞬态剂量率和稳态电离总剂量辐射效应规律。结果表明：瞬态剂量率闭锁效应对处理器造成了显著的潜在损伤，导致其总剂量失效阈值从1 030 Gy(Si)降低至600 Gy(Si)。研究结论对于大规模集成电路的可靠性评估和指导辐射加固设计有重要参考意义。     

Corrosion and mechanical properties of plasma electrolytic oxidation‐coated AZ80 magnesium alloy

Plasma electrolytic oxidation (PEO) coatings were produced on AZ80 magnesium alloy in a solution containing silicates and phosphates and working at high current densities with short treatment times. The effect of a sealing treatment in boiling water on corrosion and mechanical properties of the coatings were investigated. Moreover, the corrosion mechanism of the samples with and without the sealing treatment was evaluated. The microstructure of the coatings was characterized with scanning electron microscope observation and X‐ray diffraction analysis. The mechanical properties were evaluated with nanoindentation tests and the corrosion resistance was studied by potentiodynamic polarization, electrochemical impedance spectroscopy, and scanning vibrating electrode technique. The results showed that the sealing did not influence the microstructure and the mechanical properties of the samples and instead produced a remarkable increase in the corrosion resistance. The crevice corrosion, present in the sample without the sealing, was avoided with the treatment in boiling water.