热压烧结TiB2陶瓷的显微结构和力学性能研究

以Y₂O₃－Al₂O₃为烧结助剂,通过热压制备了TiB₂陶瓷,研究了烧结温度、烧结时间和晶化处理对材料的显微结构和力学性能的影响．实验结果表明,随着烧结温度的升高,烧结体失重增加,其抗弯强度和断裂韧性降低;烧结时间延长,其显微结构的均匀性降低,对力学性能不利．晶粒直径对TiB₂陶瓷的力学性能有重要影响．晶化处理能够导致晶界拆出YAG相,从而提高TiB₂陶瓷的高温抗弯强度．     

氧化铝复合陶瓷烧结工艺研究与力学性能改善

研究了反应结合Al₂O₃－ZrO₂－SiC复合陶瓷的烧结工艺与力学性能改善途径,对快速烧结与Ar气氛常压烧结工艺及材料力学性能进行对比,并分析了微观结构．实验结果表明,快速烧结是抑制晶粒生长、获得均匀、细微、致密结构的有效途径,材料的力学性能也达到了较好水平,但其工艺难度大,而Ar气氛常压烧结工艺简便易行,也可获得相当水平的力学性能．经热等静压使材料充分致密化,消除缺陷,力学性能大幅度提高．     

原位增强SiC陶瓷

实验采用β-SiC为起始原料,Y₂O₃、A1₂O₃为烧结助剂,通过适当的烧结控制,获得了具有长柱状晶粒结构的α－SiC陶瓷,材料以液相烧结机制密化,在烧结过程中发生了与柱状晶形成有关的SiC晶粒3C→4H相变．材料的力学性能与晶粒的形态即长径比存在一定的依从关系,并显示出原位增强的特性．在较佳工艺条件下,材料的强度和韧性最大值分别达到620MPa、6．1MPa.m^1/2．压痕裂纹扩展的途径表明,裂纹偏转和晶粒桥联是主要的增韧机理,这得益于其弱的界面结合．     

β-Si3N4粉末烧结及其显微结构形成

由β－Ｓｉ_３Ｎ_４粉末通过一定的工艺条件得到致密的氨化硅陶瓷,试样的显微结构为短柱状和等轴状颗粒交织排列而成的均匀结构．材料的烧结过程分为重排、晶形转变、晶粒生长三个阶段,随烧结时间增加,烧结试样的显微结构开始阶段变化很明显,２ｈ后结构比较稳定．温度升高有利于柱状颗粒长径比的提高,添加剂量的增加使显微结构粗化．     

无压烧结氮化硅陶瓷的力学性能和显微结构

以MgO-Al₂O₃-SiO₂为烧结助剂,借助XRD、SEM、TEM、EDS、HRTEM等手段,研究了无压烧结氮化硅陶瓷材料的力学性能和显微结构,着重探讨了材料制备工艺、力学性能和显微结构之间的关系,通过调整制备工艺改善材料微观结构以提高材料的力学性能.强化球磨混合的试样经1780℃无压烧结3h后,抗折强度高达1.06GPa,洛氏硬度92,显微硬度14.2GPa,断裂韧性6.6MPa·m^0.5.材料由长柱状β-Si₃N₄晶粒组成,晶粒具有较大的长径比,长柱晶的近圆晶粒尺寸0.3-0.8μm,长度3-6μm,长径比约7-10,显微结构均匀.     

添加Y2O3-Dy2O3的AlN陶瓷的烧结特性及显微结构

本文探索了以自蔓延高温（SHS）法合成并经抗水化处理的AlN粉为原料,以Y₂O₃－Dy₂O₃作为助烧结剂的AlN陶瓷的烧结特性及显微结构．结果表明,晶界处存在Dy₄Al₂O₉、Y₄Al₂O₉、DyAlO₃、Dy₂O₃和DyN等第二相物质,随烧结温度变化,第二相的种类、数量和分布不同,显微结构也随之变化,从而影响AlN的热导率．在1850℃下,可获得热导率为148W／m·K的AlN陶瓷．     

以Al-B-C为烧结助剂的SiC陶瓷热压烧结工艺

以SiC超细粉末为原料,Al粉、B粉和碳黑为烧结助剂,采用热压烧结工艺制备了SiC陶瓷,重点研究了烧结助剂含量(4～13 wt％)对SiC陶瓷物相组成、致密度、断面结构及力学性能的影响.除SiC主晶相外,X射线衍射图还显示了Al8B4C7相的存在;当烧结助剂的含量从4 wt％增至13 wt％时,扫描电镜照片显示陶瓷断面形貌从疏松结构变成致密结构,存在晶粒拔出现象;陶瓷力学性能随着烧结助剂含量的增加先升高后降低.当烧结助剂含量为10 wt％时,SiC陶瓷的力学性能达到最高,抗弯强度为518.1 MPa,断裂韧性为4.98 MPa·m1/2.Al、B和C烧结助剂在1850℃烧结温度下形成的Al8B4C7液相促进晶粒间的重排和传质,并填充晶粒间的气孔,提高了陶瓷致密度.     

高温等静压烧结碳化硅基复相陶瓷的强化与增韧

本文通过Si₃N₄、TiC及SiC晶须补强SiC基复相陶瓷的高温等静压烧结,研究了复相陶瓷的显微结构与力学性能,探讨了晶须及第二相颗粒对复相陶瓷的强化与增韧机理．结果表明,不同的补强颗粒及晶须在基体中的作用也不同,Si₃N₄的引入将在基体与第二相颗粒之间产生径向压应力,阻碍裂纹的扩展,TiC的引入将在基体与第二相颗粒之间产生径向张应力,诱导裂纹的偏转;SiC晶须的引入也将产生阻碍裂纹扩展的机制,从而达到SiC基复相陶瓷强化与增韧,改善其力学性能．     

热压烧结固溶复合TiB2-NbB2陶瓷的结构与性能

过渡金属硼化物与TiB₂具有相同的晶体结构和相近的晶格常数,因此通过适当的工艺手段能够与TiB₂形成固溶体.本文以NbB₂作为掺加剂,通过热压烧结制备了TiB₂-NbB₂固溶复合陶瓷.研究了掺加剂含量对烧结材料力学性能的影响,材料的显微结构分别由EPMA、SEM和TEM测定.研究结果表明,NbB₂可以部分固溶到TiB₂中形成固溶体,并有助于细化TiB₂晶粒,同时材料的力学性能得到提高.     

放电等离子超快速烧结氧化物陶瓷

本文介绍一种氧化物陶瓷超快速烧结的新方法．用放电等离子烧结的方法对Al₂O₃、Y-TZP、YAG、Al₂O₃-ZrO₂2和莫来石等各种氧化物粉体进行了超快速烧结,采用2～3min升温到1200℃以上,不保温或保温2min,然后迅即在3min之内冷却至600℃以下的烧结温度,得到了直径为20mm的晶粒细、致密度高、力学性能好的烧结样品．对用化学共沉淀法自制的20mol％Al₂O₃-ZrO₂（3Y）纳米粉体分别在1170～1500℃之间的7个不同温度下进行放电等离子烧结,升温速率为200℃／min,保温2min后;迅即在3min之内强制冷却至600℃以下．1350℃以上烧结得到的样品密度已接近理论密度,1250℃以上烧结得到的样品的断裂韧性K1c都大于6MPa·m^1/2放电等离子超快速反应烧结所得到的ZrO₂-莫来石复相陶瓷致密度高、力学性能好,ZrO₂晶粒在莫来石基体中分布均匀,XRD结果表明,在1530℃烧结的样品中,已找不到ZrsiO₄痕迹,说明在如此快速的烧结条件下;反应烧结已经可以完成．     

Effects of sintering conditions on the microstructure and mechanical properties of SiC prepared using powders recovered from kerf loss sludge

The effects of sintering conditions on the microstructure and mechanical properties of the sintered SiC prepared using the SiC powder recovered from the kerf loss sludge were investigated. The recovered SiC powders were consolidated by spark plasma sintering (SPS) and conventional sintering methods. The effects of sintering temperature, time and methods (SPS and conventional sintering) on the phase, grain size and density of SiC were systematically studied. The Vickers hardness of spark plasma-sintered (SPSed) samples was higher than that of conventional sintered samples due to small grain size. When holding time was increased from 10 to 30 min, the grain size and relative density of SPSed samples were also increased, which lead to the almost constant Vickers hardness by competing effects of grain size and relative density. When holding time was over 30 min, no appreciable change of the relative density and grain size were observed, which can lead to similar values of Vickers hardness. SPS process can be used to make SiC with high density and hardness at relatively low temperature compared with the conventional sintering process.     

新型多孔碳化硅陶瓷膜管的制备与性能表征

以SiC为骨料,选用低共熔混合物作为烧结助剂,用液相烧结技术制备出单通道多孔陶瓷支撑体,采用悬浮粒子浸涂法对支撑体涂覆氧化铝膜.考察了氧化铝膜、烧成温度对支撑体孔径分布和空气渗透通量等性能的影响.结果表明:涂膜后膜管的孔径分布变窄,空气渗透通量略有下降;随着烧结温度的提高,结合剂的高温特性使得支撑体的开孔率和空气渗透通量分别下降了1.9%和17.9 m3/(m2·h),孔径分布变宽,平均孔径增大.     

熔盐辅助合成Dy3Si2C2包裹SiC粉体及其陶瓷的烧结行为

碳化硅陶瓷因自身优良的物理化学性能而具有广泛的应用前景.碳化硅的化学键结合特性决定了其难以烧结成型,因此如何制备高质量碳化硅陶瓷是领域内的难点之一.本研究以三元稀土碳化物Dy3Si2C2作为新型SiC陶瓷的烧结助剂,依据Dy-Si-C体系的高温相转变原位促进碳化硅的烧结致密化.采用放电等离子烧结技术,利用金属Dy与Si...     

亚微米Al2O3对重结晶碳化硅的作用机制

使用不同粒径的SiC和亚微米Al₂O₃添加剂制备重结晶烧结碳化硅并表征其物相组成、微观形貌、孔径分布和耐压性能,研究了亚微米Al₂O₃对重结晶碳化硅的作用机制。结果表明,在亚微米Al₂O₃作用下,重结晶碳化硅的烧结过程可分为液相烧结和重结晶烧结两个阶段。在液相烧结过程中高活性的亚微米Al₂O₃促进了液相的形成,使SiC的传质方式由扩散传质演变为粘性流动传质。在重结晶烧结温度SiC的传质以蒸发-凝聚为主,形成含铝气相并与SiC固溶促进了6H-SiC向4H-SiC晶型的转变。引入亚微米Al₂O₃后,重结晶碳化硅材料的孔径分布由单峰分布转变为多峰分布,其中孔径较小的特征峰对应重结晶烧结形成,而较大孔径的特征峰则来源于液相烧结的形成;同时,随着保温时间的延长SiC晶粒生长发育更为完全,由不规则颗粒状转变为较规则六方结构。但是,体积密度的下降、SiC晶粒尺寸不均一以及材料孔径的多...     

Preparation and mechanical properties of ZrB<Subscript>2</Subscript>-based ceramics using MoSi<Subscript>2</Subscript> as sintering aids

ZrB₂ (zirconium diboride)-based ceramics reinforced by 15vol.% SiC whiskers with high density were successfully prepared using MoSi₂ as sintering aids. The effects of sintering condition and MoSi₂ content on densification behavior, phase composition, and mechanical properties of SiC_w/ZrB₂ composites were studied. Nearly, fully dense materials (relative density >99%) were obtained by hot-pressing (HP) at 1700°C–1800°C in flow argon atmosphere. The grain size of ZrB₂ phase in the samples sintered by HP at 1700°C–1800°C were very fine, with mean size below 5 μm. Mechanical properties (such as flexural strength, fracture toughness, and Vickers hardness) of the sintered samples were measured. The sample with 15vol.% MoSi₂ addition sintered by HP at 1750°C displayed the best mechanical properties.     

Preparation and mechanical properties of ZrB2-based ceramics using MoSi2 as sintering aids

ZrB₂ (zirconium diboride)-based ceramics reinforced by 15vol.% SiC whiskers with high density were successfully prepared using MoSi₂ as sintering aids. The effects of sintering condition and MoSi₂ content on densification behavior, phase composition, and mechanical properties of SiC_w/ZrB₂ composites were studied. Nearly, fully dense materials (relative density >99%) were obtained by hot-pressing (HP) at 1700°C–1800°C in flow argon atmosphere. The grain size of ZrB₂ phase in the samples sintered by HP at 1700°C–1800°C were very fine, with mean size below 5 μm. Mechanical properties (such as flexural strength, fracture toughness, and Vickers hardness) of the sintered samples were measured. The sample with 15vol.% MoSi₂ addition sintered by HP at 1750°C displayed the best mechanical properties.     

Microstructure–mechanical properties relations in SiC–TiB2 composite

Densification and mechanical properties (fracture toughness, flexural strength and hardness) of SiC–TiB₂ composite were studied. Pressureless sintering experiments were carried out on samples containing 0–50 vol% of TiB₂ created by in situ reaction between TiO₂, B₄C and carbon. Al₂O₃ and Y₂O₃ were used as sintering additives to create liquid phase and promote densification at sintering temperature of 1940 °C. The sintered samples were subsequently heat treated at 1970 °C. It was found that the presence of TiB₂ serves as an effective obstacle to SiC grain growth as well as crack propagation thus increasing both strength and fracture toughness of sintered SiC–TiB₂ composite. The subsequent heat treatment of sintered samples promoted the elongation of SiC matrix and further improved mechanical properties of the composite. The best mechanical properties were measured in heat-treated samples containing 12–24 vol% TiB₂. The maximum flexural strength of ∼600 MPa was obtained in samples with 12 vol% TiB₂ whereas the maximum fracture toughness of 6.6 MPa m^1/2 was obtained in samples with 24 vol% TiB₂. Typical microstructures of samples with the mentioned volume fractions of TiB₂ consist of TiB₂ particles (<5 μm) uniformly dispersed in a matrix of elongated SiC plates.     

残余相和烧结温度对碳化硅陶瓷抗混酸腐蚀特性的影响

本工作主要研究了残余相和晶粒尺寸对碳化硅的抗混酸(HF-HNO₃)腐蚀特性。通过不同的烧结方法(固相烧结、液相烧结、反应烧结)制备出残余相不同的碳化硅材料。结果表明: 与液相烧结碳化硅(LPS SiC)和反应烧结碳化硅(RB SiC)相比, 固相烧结碳化硅(SSiC)具有更好的腐蚀抗性, 这是由于残余相石墨的抗腐蚀性强, 以及残余相在材料中形成不能相互联通的岛状结构。通过调节碳化硅的烧结温度, 可以影响材料中的晶粒尺寸, 研究结果发现相同烧结温度下随着残余相含量的增加, 材料腐蚀失重线性增加, 对曲线进行线性拟合, 其Y轴截距的绝对值代表不含碳的试样在该烧结温度下的腐蚀失重。研究表明随着烧结温度由2100℃升高到2160℃, 晶粒尺寸由2 μm增加到6 μm。此时其Y轴截距的绝对值分别为9.22(2100℃), 5.81(2130℃), 0.29(2160℃), 表明晶粒尺寸的增加有利于提高材料的抗腐蚀能力。     

无压烧结Ti3SiC2/铝基复合材料组织与性能

MAX相具有独特的层状晶体结构,不但具备常用铝基复合材料外加陶瓷颗粒的性能特征,同时具有可与石墨媲美的摩擦性能.本文以Al粉、Si粉和典型MAX相Ti_3SiC_2为原料,采用冷压成型-无压烧结方法制备了Ti_3SiC_2/Al-Si复合材料,并通过金相显微镜、X射线衍射仪(XRD)、扫描电镜(SEM)、能谱仪(EDS)等分析手段,研究了烧结温度、Si元素含量对复合材料组织与性能的影响.研究表明:随着烧结温度从500℃提高到700℃,复合材料致密度先上升后下降,摩擦系数先降低后上升,硬度逐渐增大至最大值并基本保持稳定;随着Si质量分数从0增加到20.7%,复合材料的致密度逐渐降低,硬度逐渐增大,摩擦系数先降低后增大,晶粒尺寸随之下降,12.5%Si晶粒最为细小;烧结温度为650℃,Si元素质量分数为12.5%的铝基复合材料具有最低的摩擦系数0.18,相应的硬度为62 HV,致密度为92.12%.XRD物相和扫描电镜组织分析表明,复合材料的主要相组成为Al、Ti_3SiC_2,及由界面反应产生的Al_4C_3和Al的氧化产物Al_2O_3.     

Spark plasma sintering on nanometer scale WC–Co powder

Nanometer scale WC–11Co powder was sintered by spark plasma sintering (SPS) process in order to improve the properties of the cemented carbides. Properties such as density and hardness were measured. The microstructures of sintered WC–11Co cemented carbides were observed. The grain size of WC in alloys was also obtained. The results showed that spark plasma sintering could lower the sintering temperature, increased the density and circumscribed the growth of grain size of WC. Besides, the hardness of the sintered cemented alloys that was dependent on the grain size and densification could also be improved by SPS. SPS was an effective method to get WC–11Co cemented carbides with fine grain size and good properties.