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121.
The present study focuses on the sintering of silicon carbide-based ceramics (SiC) by liquid phase sintering (LPS) followed by characterization of the produced ceramics. AlN/Re2O3 mixtures were used as additives in the LPS process. In the first step, the LPS-SiC materials were produced in a graphite resistance furnace in the form of discs at different temperatures. The conditions with the best results regarding real density and relative density were taken as reference for sintering in the form of prismatic bars. In the second step, these samples were evaluated regarding fracture toughness (KIC), by the Single Edge V Notch Beam – SEVNB – method, and flexural strength. KIC behavior was evaluated according to the depth and curvature radius of the notches. Reliable KIC values were presented when the ceramic displayed a small curvature radius at the notch tip. When the radius was large, it did not maintain the square root singularity of the notch tip. Tests were carried out to determine KIC values in atmospheric air and water. KIC results were lower in water than air, with a decrease ranging between 2.56% and 11.26%. The observations indicated a direct grain size correlation between KIC values and fracture strength of the SiC ceramics. 相似文献
122.
In this paper, debonding phenomena between carbon fiber reinforced polymer (CFRP) strips and masonry support were investigated on the basis of single-lap shear tests, considering different dimensions of the bond length. To capture the post-peak response of the CFRP–masonry joint, the slip between the support and the reinforcement strip was controlled using a clip gauge positioned at the end of the reinforcement. The tests were simulated by means of a finite element model able to capture the post-peak snap-back behavior due to the failure process. The numerical model is based on zero-thickness interface elements and on a proper non-linear cohesive law. The comparison between experimental and numerical results was performed in terms of overall response, measured by both the machine stroke and the clip gauge positioned at the free end of the reinforcement. The cases of effective bond length greater and lesser than the minimum anchorage length, suggested by the CNR Italian recommendation, were considered. 相似文献
123.
124.
We compare the current density–voltage (J–V) and magnetoconductance (MC) response of a poly(3-hexyl-thiophene) (P3HT) device (Au/P3HT(350 nm)/Al) before and after annealing above the glass transition temperature of 150 °C under vacuum. There is a decrease of more than 3 orders of magnitude in current density due to an increase of the charge injection barriers after de-doping through annealing. An increase, approaching 1 order of magnitude, in the negative MC response after annealing can be explained by a shift in the Fermi level due to de-doping, according to the bipolaron mechanism. We successfully tune the charge injection barrier through re-doping by photo-oxidation. This leads to the charge injection and transport transitioning from unipolar to ambipolar, as the bias increases, and we model the MC response using a combination of bipolaron and triplet-polaron interaction mechanisms. 相似文献
125.
《Intermetallics》2015
Drop-tube processing was used to rapidly solidify droplets of Ni64.7Fe10Si25.3 and Ni59.7Fe15Si25.3 alloys. In the larger droplets, and therefore at low cooling rates, only two phases, γ-Ni31Si12 and β1-Ni3Si were observed. Conversely, in the smaller droplets, and therefore at higher cooling rates, the metastable phase Ni25Si9 was also observed. The critical cooling rate for the formation of Ni25Si9 was estimated as 5 × 103 K s−1. SEM and TEM analysis reveals three typical microstructures: (I) a regular structure, comprising single-phase γ-Ni31Si12 and a eutectic structure between γ-Ni31Si12 and β1-Ni3Si; (II) a refined lamellar structure with a lamellar spacing <50 nm comprising γ-Ni31Si12 and β1-Ni3Si; (III) an anomalous structure with a matrix of Ni25Si9 and only a very small proportion of a second, and as yet unidentified, phase. These results indicate that there is an extended stability field for Ni25Si9 in the Ni-rich part of the Ni–Fe–Si ternary system in comparison to the Ni–Si binary system. With an increase of cooling rate, an increasing fraction of small droplets experience high undercoolings and, therefore, can be undercooled into the Ni25Si9 stability field forming droplets consisting of only the anomalous structure (III). The Fe atoms are found to occupy different substitutional sites in different phase, i.e. Fe substitutes for Ni in the γ phase and Si in the L12 (β1) phase respectively. 相似文献
126.
127.
Ponnusamy Nandha Kumar Shangavi Subramanian Uthirapathy Vijayalakshmi Sanjeevi Kannan 《Journal of the American Ceramic Society》2020,103(6):3528-3540
Structurally stable β-Ca3(PO4)2/t-ZrO2 composite mixtures with the aid of Dy3+ stabilizer were accomplished at 1500°C. The precursors comprising Ca2+, P5+, Zr4+, and Dy3+ have been varied to obtain five different combinations. The results revealed the fact that complete phase transformation of calcium-deficient apatite to β-Ca3(PO4)2 occurred only at 1300°C, whereas the evidence of t-ZrO2 crystallization is obvious at 900°C. The dual occupancy of Dy3+ at β-Ca3(PO4)2 and t-ZrO2 structures was evident; however, Dy3+ initially prefers to occupy β-Ca3(PO4)2 lattice until its saturation limit and thereafter accommodates at the lattice site of ZrO2. The typical absorption and emission behavior of Dy3+ were noticed in all the systems and, moreover, the surrounding symmetry of Dy3+ domains has been determined from the luminescence study. All the systems ensured paramagnetic response that is generally contributed by the presence of Dy3+. A gradual increment in the phase content of t-ZrO2 in the composite mixtures ensured a significant improvement in the hardness and Young's modulus of the investigated compositions. 相似文献
128.
129.
针对现代消费类电子产品快速更新换代的现状, 介绍了该类产品的自动化生产线成组技术,阐述了通过度量消费类电子产品相似性和派生性特征,对产线进行成组编码的原理,研究产线工位单元的建模方法,描述了建模内容,并通过有无装载板的产线结构,论述了产线成组编码集成的途径和方法. 相似文献