Densification kinetics of boron carbide with medium entropy alloy as a sintering aid during spark plasma sintering

The high sintering temperature of pure B₄C considerably limits its widespread application, thus searching an effective sintering aid is critical. In this work, B₄C-based ceramic with 1 vol.% nonequiatomic Fe₅₀Mn₃₀Co₁₀Cr₁₀ medium entropy alloy as a sintering aid were fabricated at 1900-2000°C by spark plasma sintering (SPS) under applied pressure, and their mechanical properties were examined and compared with pure B₄C ceramic sintered at same condition. The maximal flexural strength of 255.59 MPa, microhardness of 2297.6 Hv_0.2 and fracture toughness of 3.62 MPa m^1/2 could be obtained at optimized SPS pressure of 50 MPa, which were all higher than those of pure B₄C ceramic. To better understand the densification kinetics mechanisms, the densification ratio as a function of SPS temperature and pressure was theoretically analyzed using steady creep model. It was found that densification controlled by grain-boundary sliding at lower pressure transferred to power law creep regime at higher pressure, which were proved by the dislocation net shown in transmission electron microscopy image.     

Micro-structure of ITO ceramics sintered at different temperatures and its effect on the properties of deposited ITO films

Structural characterizations of two ITO ceramics that were respectively sintered at 1560 °C and 1600 °C were focused on and the results indicate that the lower sintering temperature is good for ITO ceramics to have the triangle fine grains, larger elemental concentration gradients of indium and tin and more content of In₄Sn₃O₁₂ phase which displays the stronger grain orientation growth along the crystallographic direction of [0-11]. ITO films with 100 nm thickness deposited at 25 °C–230 °C were used to investigate the effect of micro-structure on the film properties. Grain orientation growth of In₄Sn₃O₁₂ phase is conductive to form ITO films of columnar structure. Otherwise, uniform micro-structure and higher solubility of SnO₂ in In₂O₃ main phase contribute to deposit ITO films of higher sheet resistance, less thickness uniformity and higher transmittance at 25 °C, smaller etching angle and lower etching rate at 230 °C.     

Microstructure and Mechanical Properties of Selective Laser Melted Al-2.51Mn-2.71Mg-0.55Sc-0.29Cu-0.31Zn Alloy Designed by Supersaturated Solid Solution

Selective laser melting (SLM) of aluminium alloys for lightweight application is arousing widespread interest, but the available alloy compositions are limited due to unsatisfactory mechanical performances. The rapid solidification of SLM provides a pathway to design a novel alloy composition with extended solubility. This strategy is demonstrated by an additively manufactured novel Al-2.51Mn-2.71Mg-0.55Sc-0.29Cu-0.31Zn alloy with the supersaturated solid solution in the present study. The microstructure of as-build sample is characterized with multi-modal grains with the fine equiaxed grain (FEG, ~ 800 nm) at molten pool boundaries, coarse equiaxed grain (CEG, ~ 2 μm) and columnar dendrites (CD, ~ 4 μm) inside the molten pool, which relates to the precipitations type and distribution. It is observable that Al₃(Sc, Zr) precipitation particles with the size of ~ 50 nm are dispersed in the FEG zone, while the interior of CEG shows no Al₃(Sc, Zr) particle which only exists at the CEG boundaries. Regardless of FEG, CEG or CD, the slender Al₆Mn precipitation with the length of ~ 500 nm is distributed along the grain boundaries. Meanwhile, a lot of vacancies and thickness fringes are detected in the FEG zone, which confirms the supersaturated solid solution in laser rapid solidification. The ultimate tensile strength and yield strength of the as-printed sample are ~ 380 MPa and ~ 330 MPa, respectively, with elongation ~ 14%, which increase to ~ 440 MPa and ~ 410 MPa with a reduction of elongation to ~ 9% after heat treatment.     

Effect of grain size on tribological behavior of hot-pressed boron carbide sliding against alumina balls

Boron carbide ceramics (B₄C) have extraordinary hardness and well-abrasive resistance, while the tribological behavior of ceramic materials is complicated, which are affected by microstructures, mechanical properties, and surface characteristics, and so on. In this paper, the effect of grain size on the mechanical properties especially the wear resistance of hot-pressed B₄C was investigated. The average coefficient of friction of the B₄C/Al₂O₃ friction pair ranges from .41 to .66. The sample with the minimum grain size possesses the lowest wear rate of about 2.15 × 10⁻⁶–7.66 × 10⁻⁶ mm³∙N⁻¹∙m⁻¹. The analysis of the wear rate (W_R) and grain size (G) indicates that the wear resistance (W_R⁻¹) and the reciprocal of the square root of grain size (G^−1/2) are in line with the Hall–Petch relation. Fracture and the resulting abrasive wear are the main wear mechanisms of B₄C in the dry sliding process. This success provides a theoretical basis and a design approach of microstructure to improve the tribological behavior of ceramic materials.     

认真落实"十六字工作体系"继续深化切实做好煤矿瓦斯治理工作

从认识、工作规划、领导、经验借鏊、监管监察等方面,提出了贯彻通风可靠、抽采达标、监控有效、管理到位"十六字工作体系"的方法.提出了切实做好当前煤矿安全工作的5条措施:深入开展隐患排查治理;加大煤矿整顿关闭工作力度,狠抓煤矿安全基础管理;严格追究煤矿事故责任;抓好汛期煤矿安全工作.     

PLC在电气自动化控制系统中应用范例

介绍安钢六机六流小方坯自动控制系统的设计方案及配置,并针对系统运行中出现的问题,进行控制措施的改进。     

A Comparative Study on the Microstructure and Properties of ITO Targets and Thin Films Prepared from Two Different Powders

With the rapid development of indium tin oxide(ITO) in the electronic display industry, choosing which raw powders to prepare high-quality ITO targets has always been a controversial topic. In the work, in order to clearly understand the effect of the raw powders on the microstructure and properties of ITO targets and thin films, tin-doped indium oxide(dITO) and In_2O_3-SnO_2 mixed(mITO) powders were chosen to prepare ITO targets for depositing the films and a comparative study on their microstructure and properties was conducted. It is found that,(1) dITO targets possess a higher solid solubility of tin in indium oxide and more uniform elemental distribution, while there are a higher density, a finer grain size and a higher mass ratio of In_2 O_3 to SnO_2 for the mITO targets;(2) dITO films with more coarser columnar grains and a rougher surface prefer to grow along the [100] direction in an Ar atmosphere;(3) the conductive property of ITO films only depends on the doping amount of tin and is independent of the raw powders and the preparation process of the target source;(4) dITO films possess the superior optical property and narrower optical band gap;(5) the etching property of mITO films is superior to that of dITO films due to the lower solid solubility of tin in indium oxide.     

韧性城市视角下的甬江流域数字孪生平台建设

针对甬江流域水灾害防御需求,结合韧性城市理论,以防洪减灾“预报、预警、预演、预案”四预体系为导向,利用数字孪生引擎的强大渲染能力,建设全要素的数字孪生流域时空底座,以水文水动力模型、空间计算技术等为重要基础支撑,围绕综合监测、洪涝预报、洪涝预演、综合调度、协同预案等业务需求构建孪生场景,实现了甬江流域数字孪生平台。实践应用表明,该平台成功抵御了甬江流域超标准洪水,并对未来防洪工程体系优化具有启示意义,对其他流域防洪减灾、城市内涝治理工作具有一定的借鉴意义。