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51.
Spark plasma sintering (SPS) has been used to synthesise samples of a model dual-phase (DP) system, consisting of copper and AISI420 martensitic steel. Mixed powders were sintered at different temperatures in the range from 850°C to 1000°C using a loading pressure of 60?MPa. Tensile testing revealed dimpled fracture surfaces in samples sintered at higher temperatures, indicating ductile failure and good interfacial bonding between the phases, with the best results overall obtained for samples sintered from wet-mixed powders. The results show that by control of the mixing, sintering and post-sintering heat treatment conditions, the fabrication of dense samples covering a range of DP microstructures is possible using SPS, with independent control of the microstructure and properties of the two phases. 相似文献
52.
《Ceramics International》2020,46(14):22005-22014
This present work investigated the mechanical properties and microstructure of h-BN based ceramic composites reinforced with CNTs and GNPs. Accordingly, two different batches of pure h-BN, h-BN/0.1 wt%CNTs and h-BN/0.1 wt% GNPs were prepared through a high energy mixer mill to gain a uniform dispersion of reinforcement with the initial stable CNTs or GNPs solution in ethanol. After drying the mixtures, the pure h-BN and also, two different composite components were directly inserted into the graphite mold and the sintering process was performed with the initial and final pressure of 10 and 50 MPa, respectively, at 1900 °C, under the vacuum condition of 15–35 Pa. The relative density of the samples was calculated based on the Archimedes principle. The densification behavior of the samples showed the maximum amount of 98.31% for the theoretical density of the h-BN/GNPs composite. On the other hand, the minimum relative density of 96.41% was obtained for the h-BN/CNTs composite. The microstructure studies of the prepared sample showed the uniform distribution of GNPs in the h-BN layers; however, when the CNTs were added, some agglomerated area was found. Moreover, the fracture surface of all samples showed a laminar fracture as a result of the layer-by-layer structure of h-BN. The investigation of the mechanical properties of the prepared specimens also revealed the highest bending strength, fracture toughness and Vickers hardness of 199 MPa, 1.26 GPa and 3.62 MPa m−1/2, respectively, which belonged to the h-BN/GNPs composite. In the case of CNTs, this trend exhibited lower amounts, probably due to the agglomeration of CNTs. 相似文献
53.
针对HfB2陶瓷材料难烧结和韧性差等问题,选择ZrC粉、Si粉和C粉为烧结助剂,借助ZrC-Si-C间的原位反应生成ZrSi2和SiC,促进HfB2陶瓷的烧结,并提高HfB2陶瓷的综合力学性能。结果表明,HfB2与烧结助剂的混合粉体经放电等离子烧结(SPS)在1600℃保温10 min和40 MPa的压力条件下制备出相对密度为96.6 1%的HfB2-ZrSi2-SiC复合材料,所制样品的硬度、抗弯强度和断裂韧性均随着烧结助剂ZrC-Si-C含量的增加呈现先上升后降低的趋势。当ZrC-Si-C添加量为10%时所制备样品的综合力学性能最好,其硬度值为26.80±1.2 GPa、抗弯强度为504±40 MPa、断裂韧性值为4.66±0.21 MPa·m1/2。 相似文献
54.
随着信息化的深入,大数据在各个领域产生了巨大的价值,海量数据的存储和快速分析成为新的挑战。传统的关系型数据库由于性能、扩展性的不足以及价格昂贵等方面的缺点,难以满足大数据的存储和分析需求。Spark SQL是基于大数据处理框架Spark的数据分析工具,目前已支持TPC-DS基准,成为大数据背景下传统数据仓库的替代解决方案。全文检索作为一种文本搜索的有效方式,能够与一般的查询操作结合使用,提供更加丰富的查询和分析操作。目前,Spark SQL仅支持简单的查询操作,不支持全文检索。为了满足传统业务迁移和现有业务的使用需求,提出了分布式全文检索框架,涵盖了SQL文法、SQL翻译转换框架、全文检索并行化、检索优化4个模块,并在Spark SQL上进行了实现。实验结果表明相比于传统的数据库,在两种检索优化策略下,该框架的索引构建时间、查询时间分别减少到传统数据库的0.6%/0.5%和1%/10%,索引存储量减少为传统数据库的55.0%。 相似文献
55.
Kuo-Hsiung Tseng Juei-Long Chiu Heng-Lin Lee Yi-Syuan Kao Der-Chi Tien 《Materials and Manufacturing Processes》2016,31(2):186-193
This study developed a system monitoring the electric discharge machine's (EDM) discharge energy and success rate to replace conventional oscilloscope observation. By using logic circuit, the signals are transmitted to the PC monitoring platform in order to display the discharge success times, discharge success rate, and electrode's consumption energy. The advantage of the proposed system is the capability to observe real-time discharges and record the experimental conditions, as well as optimize the discharge parameter settings. The experimental results suggest that, in the preparation of nanosilver colloid, the cost-performance of Ton–Toff at 10–100 µs is the optimal setting. The monitoring system also can take advantage of the discharge success rate to control the energy consumption of the electrode to obtain the standardization of products. The results suggest that, while discharge success rate, electrode's weight loss and wavelength of the absorption peak are considerably accurate, but concentration accuracy is relatively poor. The discharge success rate monitoring system is an innovative method that can help to realize electric discharge processing, optimize product quality, and it may be a powerful processing tool in the future. 相似文献
56.
《International Journal of Hydrogen Energy》2019,44(36):20345-20354
Using a citrate-nitrate process, BaCe0.9-xZrxY0.1O3-δ (x = 0, 0.5, 0.6, 0.7 and 0.8) nanopowders were synthesized, on the basis of which proton-conducting solid electrolytes (average size of coherent scattering region (CSR) - 15–53 nm) were obtained by spark plasma sintering (SPS) at a low temperature (900°С). The dependence of phase composition, microstructure and electrophysical properties of the obtained samples on ZrO2 content and consolidation conditions was established. It was found that the BaCe0.4Zr0,5Y0.1O3-δ solid solution had the highest electrical conductivity among zirconium-containing ceramic materials in the studied concentration range. It was shown that SPS is a promising method for obtaining solid electrolytes for proton-conducting solid oxide fuel cells (PCFC) at lower temperatures (by 400–500°С), compared to traditionally-used temperature conditions (1400–1800 °C). 相似文献
57.
Farzad Shayesteh Seyed Ali Delbari Zohre Ahmadi Mohammadreza Shokouhimehr Mehdi Shahedi Asl 《Ceramics International》2019,45(5):5306-5311
In this study, the impact of TiN as a sintering aid on the relative density and microstructure of TiB2 ceramic was investigated. Monolithic TiB2 and TiB2 doped with 5?wt% TiN were sintered at 1900?°C for 7?min dwell time under the pressure of 40?MPa by spark plasma. The addition of TiN affected the microstructure of TiB2-based sample considerably depicting the finer grains in the as-sintered ceramic. X-ray diffraction evaluation indicated that no interaction occurred between the initial materials. However, detail investigation by the map analysis and energy dispersive spectroscopy results revealed the formation of in-situ nano-sized hBN secondary phase in the TiN-doped TiB2. In addition, TiN played a remarkable role on increasing the relative density of TiN-doped TiB2 ceramic producing a nearly fully dense ceramic with relative density of 99.9% in comparison with the monolithic ceramic having 96.7% relative density. 相似文献
58.
Babak Mohammadpour Zohre Ahmadi Mohammadreza Shokouhimehr Mehdi Shahedi Asl 《Ceramics International》2019,45(4):4262-4267
This research presents the influence of Al addition on microstructure and mechanical behavior of ZrB2–SiC ultra-high temperature ceramic matrix composite (UHTCMC) fabricated by spark plasma sintering (SPS). A 2.5?wt% Al-doped ZrB2–20?vol% SiC UHTCMC was produced by SPS method at 1900?°C under a pressure of 40?MPa for 7?min. The microstructural and phase analysis of the composite showed that aluminum-containing compounds were formed in-situ during the SPS as a result of chemical reactions between Al and surface oxide films of the raw materials (i.e. ZrO2 and SiO2 on the surfaces of ZrB2 and SiC particles, respectively). The Al dopant was completely consumed and converted to the intermetallic Al3Zr and Al4Si compounds as well as Al2O3 and Al2SiO5. A relative density of 99.8%, a hardness (HV5) of 21.5?GPa and a fracture toughness (indentation method) of 6.3?MPa?m1/2 were estimated for the Al-doped ZrB2–SiC composite. Crack bridging, branching, and deflection were identified as the main toughening mechanisms. 相似文献
59.
《Journal of the European Ceramic Society》2019,39(16):5350-5357
In MgAl2O4 (Mg aluminate) fabricated by pressure sintering, carbon contamination, oxygen vacancy, and other defects exist and cannot be completely removed even after post-annealing. ZnAl2O4 (Zn aluminate) has the same crystallographic structure as Mg aluminate and excellent light transmission by post-annealing. In this study, the transmission of (Mg1-XZnX)Al2O4 spinel, which is a solid solution between Mg aluminate and Zn aluminate, was investigated. After post-annealing, the transmission of (Mg1-XZnX)Al2O4 spinel was higher than Zn aluminate and Mg aluminate, which means that the absorption center disappeared. Besides, the real in-line transmission is improved by up to 30% by post-annealing, which is related to the driving force to increase the configurational entropy and form a more stable solid solution phase. In solid solution spinel, as the Zn content increases, the optical properties can be improved by post-annealing, but the mechanical properties are slightly decreased. 相似文献