Pressure-assisted flash sintering of ZnO ceramics

Implementing pressure-assisted flash sintering of ZnO powder without pretreatment by a new experimental configuration is presented. Rapid and energy-concentrated heating of electrode-sample-electrode area by induction heating allows preheating and flash sintering of loose-pack powder in the die with pressure assistance. Using an insulated die enables the current to flow through the sample during flash sintering. ZnO ceramics with a relative density of 95.1% can be achieved in less than 3 min. The whole process includes 104 s of preheating by a low-power induction heating device and 30 s of flash sintering assisted by a pressure of 26 MPa using the pulsed direct current (DC). The process characteristics of pressure-assisted flash sintering using the pulsed DC are discussed. The effect of pressure on densification and grain size is analyzed in detail, and some potential mechanisms are provided.     

Microstructure and Tensile Strength of the Bonded Interfaces and Parent Materials in W/ODS Steel Joints Fabricated by Direct SSDB

In the present work, Tungsten (W)/oxide dispersion strengthened (ODS) steel joints were fabricated by the direct solid state diffusion bonding (SSDB) technology with a multistage cooling process, and the microstructure and tensile strength of the bonded interfaces and parent materials were experimentally investigated. The results show that W and ODS steel can be successfully bonded at the temperature ranging from 900 °C to 1050 °C, without severe macroscopic deformation or obvious microscopic defects. Reaction layers generated at the bonded interfaces are evolutive with the bonding temperature, result in different fracture locations of the bonded joints. In the joint bonded at 950 °C, a higher interfacial strength of ~ 234.2 MPa is achieved, due to the formation of nano-scale intermetallic compound FeW. Microstructure of W remains stable after all the SSDB processes, while the lath structure of ODS steel is completely broken and transformed into the equiaxed grains, which should be responsible for the deterioration of strength. When the bonding temperature is higher than 950 °C, the pinning effect of precipitates M₂₃C₆ and nano-oxide particles on the movement of dislocations is observed.

     

UF_6气化水解工艺改进研究

介绍了湿法UF_6气化水解过程,研究了不同气化水解过程中的压力选择、气化速率与水解速率的关系、水解工艺对水解速率的影响、水解工艺对水解液温度的影响,以及不同气化水解工艺所需热量。结果表明:UF_6气化速率与水解速率成正比,水解速率为影响UF_6气化水解的主要因素;改进后的气化水解工艺有利于提高UF_6气化水解效率。     

Transport of vacuum arc plasma through an off-plane double bend filtering duct

A new magnetic macroparticle filter design consisting of an off-plane double-bend (OPDB) filter is described. The transport of the vacuum arc plasma through this OPDB filter is investigated using Langmuir and deposition probes. Films of amorphous hard carbon have been deposited using a 90° single bend and the OPDB filter and the macroparticle contents of the films are compared. The experimental results were found to be in good agreement with the simulations results based on an improved drift approximation model. The results demonstrate that OPDB filter has a relatively better transmission efficiency than the 90° single bend filter, lower macroparticle counts and is suitable for preparation of diamond-like carbon coatings with high quality.     

FeCrAl不锈钢包壳管挤压及退火工艺优化

利用光学显微镜、扫描电镜、电子背散射衍射和万能拉伸试验机等对FeCrAl合金包壳管挤压前后的微观组织、析出相及退火后的微观组织、析出相、再结晶及力学性能进行了研究。结果表明:Nb含量对FeCrAl合金中第二相的析出影响显著,高Nb含量下Laves相的析出温度和析出数量均大大提高;降低挤压温度有助于FeCrAl合金管坯中形成细小弥散第二相;随着退火温度升高,细小弥散相的析出数量呈现先增多后减少的趋势;在相同退火工艺下,800 ℃热挤压管坯的室温力学性能比950 ℃热挤压管坯的室温力学性能要更加优异。     

难熔高熵合金在反应堆结构材料领域的机遇与挑战

传统反应堆结构材料性能已趋于极限,亟需开发新型材料。难熔高熵合金是以多种难熔元素作为主元的新型金属材料,具有独特的力学、物理和化学性质,尤其在高温力学、抗辐照等方面表现出优异的性能。难熔高熵合金在第4代核裂变反应堆包壳材料、核聚变堆面向第一壁材料等关键领域具有广阔的应用前景。本文结合具有代表性的文献,围绕难熔高熵合金的力学性能、抗辐照性能、抗氧化性能阐述了其强化机制与抗辐照机理,梳理了难熔高熵合金的发展脉络,在此基础上展望了难熔高熵合金在反应堆结构材料领域的应用前景。     

A TEM analysis of nanoparticulates in a Polar ice core

This paper explores the prospect for analyzing nanoparticulates in age-dated ice cores representing times in antiquity to establish a historical reference for atmospheric particulate regimes. Analytical transmission electron microscope (TEM) techniques were utilized to observe representative ice-melt water drops dried down on carbon/formvar or similar coated grids. A 10,000-year-old Greenland ice core was melted, and representative water drops were transferred to coated grids in a clean room environment. Essentially, all particulates observed were aggregates and either crystalline or complex mixtures of nanocrystals. Especially notable was the observation of carbon nanotubes and related fullerene-like nanocrystal forms. These observations are similar with some aspects of contemporary airborne particulates including carbon nanotubes and complex nanocrystal aggregates.     

304NG在超临界水中腐蚀后氧化膜分析

研究了奥氏体不锈钢304NG(以下简称304NG)在压力为25 MPa,温度分别为500、550、600、650℃超临界水中的腐蚀行为,通过扫描电镜-电子能谱(SEM-EDX)、X射线衍射(XRD)对304NG试样氧化膜微观组织的研究表明:304NG在超临界水中腐蚀后,表面氧化膜由岛状和非岛状2种不同形貌的腐蚀相组成.其中,含岛状腐蚀相的氧化膜具有双层结构,外层为Fe3O4相,内层为Fe3O4和FeCr2O4相;不含岛状腐蚀相的氧化膜为单层结构,氧化膜中含有Fe3O4和FeCr2O4相.同时,304NG在超临界水中氧化膜存在脱落现象,氧化膜脱落程度随温度升高而加剧.     

疲劳寿命实验曲线拟合方法选择研究

疲劳寿命的分散性影响其实验曲线拟合方法的选择,通过引入极差离散系数CR,根据实验所取的不同应变水平或者应力水平下对应的CR最大值的大小,确定曲线拟合采用的最优拟合方式,并采用该原则对疲劳寿命实验数据进行曲线拟合.拟合结果表明,拟合方法选取原则有利于优化疲劳寿命实验曲线拟合.