Effect of Temperature and Strain Rate on the Hot Deformation Behaviour of Ferritic Stainless Steel

Metals and Materials International - The flow behaviour and microstructure characteristics of a ferritic stainless steel were investigated using plain strain compression test on a Gleeble 3500...     

Densification mechanism during reactive hot pressing of B4C-ZrO2 mixtures

The densification behaviors of pure B₄C and B₄C-ZrO₂ mixtures were compared during hot pressing. The results showed that in-situ formed ZrB₂ effectively enhanced the densification process of B₄C-ZrO₂ mixtures, more significantly during the intermediate stage. Within the relative density ranging from 0.75 to 0.90, the B₄C-15?wt%ZrO₂ mixture (B15Z) achieved the maximum densification rate as twice much as that of pure B₄C. The stress exponent n>3 indicated plastic deformation was the dominant densification mechanism of B15Z. The viscosities of plastic flow were evaluated using Murray-Rodger-William equation and the viscosity of B15Z was only a quarter of that in pure B₄C. The sintering activation energy was calculated to be 305.9?kJ/mol for pure B₄C and 197?kJ/mol for B15Z, respectively. It was proposed that the lower viscosity of plastic flow and activation energy accelerated the sliding and propagating motions of plastic flow, by which underlain the enhanced densification behaviors of B₄C-ZrO₂ mixtures.     

Microstructures and mechanical properties of B4C-TiB2-SiC composites fabricated by ball milling and hot pressing

B₄C-TiB₂-SiC composites were fabricated via hot pressing using ball milled B₄C, TiB₂, and SiC powder mixtures as the starting materials. The impact of ball milling on the densification behaviors, mechanical properties, and microstructures of the ceramic composites were investigated. The results showed that the refinement of the powder mixtures and the removal of the oxide impurities played an important role in the improvement of densification and properties. Moreover, the formation of the liquid phases during the sintering was deemed beneficial for densification. The typical values of relative density, hardness, bending strength, and fracture toughness of the composites reached 99.20%, 32.84?GPa, 858?MPa and 8.21?MPa?m^1/2, respectively. Crack deflection, crack bridging, crack branching, and microcracking were considered to be the potential toughening mechanisms in the composites. Furthermore, numerous nano-sized intergranular/intragranular phases and twin structures were observed in the B₄C-TiB₂-SiC composite.     

离散事件动态系统的代数模型及其控制器的分析计算

本文在离散事件动态系统的Ｐｅｔｒｉ网图形描述的基础上建立了相应的代数模型，该模型可以用来计算无竞争无回路Ｐｅｔｒｉ网的“最大状态”；该“最大状态”的计算在本文给出的动态反馈控制器中得到了应用。     

金刚石薄膜制备和评价

采用平直钨丝作热解源,并借助钨丝支架的弹性恢复力,较好地解决了热丝热解化学气相沉积法(HFCVD)合成金刚石过程中热解丝的变形问题.样品独立加热,基片温度、钨丝温度、钨丝与样品基片距离均可独立调节.装置改进后,在Si(100)上合成了面积大约45mm×25mm的比较均匀的金刚石膜.用扫描电子显微镜(SEM)、Raman光谱和X射线衍射仪对制备的金刚石膜进行了分析.     

机械合金化Fe─B非晶合金及纳米合金的形成

在适当条件下机械合金化可以形成急冷法难以得到的单一Ｆｅ６０Ｂ４０非晶合金，而在其他成分内形成亚稳纳米合金。在众多的球磨条件中，球磨机的转速是控制合金化的重要因素，空气中的氧对小颗粒界面产生了强烈的污染作用，从而抑制了原子的相互扩散，难以形成单一的非晶产物。不同球磨条件下的产物含有的非晶相的晶化温度比单一非晶相合金的晶化温度稍高，并且与球磨条件以及成分的关系不大。     

TiB2的SHS合成过程理论分析

在ＴｉＢ２陶瓷材料的自蔓延高温合成（简称ＳＨＳ）过程中，通过改变原料的起始温度，稀释剂的含量和原始颗粒的尺寸等都可以调节合成过程的绝热温度，产物中熔融相的含量，以及燃烧波蔓延的速度，人而最终影响合成产物的结构和性质。本文对上述各种关系进行了理论计算和分析，其结果对实际合成与制备过程将有着重要的指导作用。     

半透明氮化硅陶瓷的放电等离子烧结制备及性能

用放电等离子烧结(spark plasma sintering,SPS)技术,以质量分数(下同)为9%氮化铝(A1N),3%氧化镁(MgO)为烧结助剂,在1850℃烧结5min,成功制备了半透明氮化硅(Si3N4)陶瓷.半透明Si3N4陶瓷在中红外波段表现出良好的透过率,最大透过率为66.4%.SPS的快速致密化过程保证了烧结体具有良好的晶体结构,有利于提高透过率.SPS快速的烧结过程和A1N和MgO的加入能够有效抑制烧结过程中Si3N4陶瓷由α相向β相的转变,是制备光学性能良好的Si3N4陶瓷的关键.报道了半透明Si3N4陶瓷的其他性能.光学性能与其他性能的结合,势必大大拓宽Si3N4陶瓷的应用领域.     

Influence of Fe/Ni/Al additive on the sintering behaviors of TiB<Subscript>2</Subscript> cermets

Fe-Ni-Al mixtures as hot-pressing sintering additive to Titanium diboride (TiB₂) were studied. It is found that liquid alloy formed under high temperature hardly has effects on the densification behaviors of TiB₂-independent. Fe-Ni-Al additive just works as filler between TiB₂ particles and does not change the TiB₂-independent sintering behaviors. Pressing mode has a great effect on the liquid flowing between TiB₂ particles. Multiple-steps pressing mode will give more time and space for the liquid flowing and improve the relative density of TiB₂-Fe-Ni-Al cermet.     

云环境下基于本体的用户行为分析引擎研究

针对当前大型互联网站提升用户体验的需求,本研究创造性地提出基于本体的用户行为分析引擎的思想,它通过上下文感知技术,实时获取用户访问页面时的上下文信息(以下也称为动态行为),基于本体对用户行为建模,建立基于规则的上下文推理算法,对监测到的动态用户行为进行实时推理,及时反馈结果信息给用户。实验表明:本研究理论上独辟蹊径,设计实现上结合了云存储技术,能够一定程度改善用户体验效果。