含稀土助烧剂氮化硅陶瓷的热导率、强度及电学性能

高热导率氮化硅陶瓷作为基板材料有着广泛的应用前景.如何在尽可能保持氮化硅陶瓷机械性能的前提下,提高其热导率是其实际应用的关键,而选择适当的烧结助剂是提高热导率的一个重要途径.本文研究了稀土氧化物种类及CaO、MgO烧结助剂对氮化硅陶瓷的热导率及电学和机械性能的影响,分别采用Y2O3-MgO,Y2O3-CaO,CeO2-MgO,CeO2-CaO,La2O3-MgO和La2O3-CaO 6种烧结助剂,采用放电等离子烧结后热处理的工艺制备氮化硅陶瓷.研究结果表明:氮化硅陶瓷的热导率随着烧结助剂稀土元素阳离子半径的增大有减小的趋势;与添加MgO助烧结相比,添加CaO助烧结不利于氮化硅柱状晶的生长,热导率及强度普遍较低,但硬度较高.采用Y2O3-MgO助烧剂和适当的烧结工艺,可以得到热导率高于80 W/m·K、抗弯强度大于1000 MPa、体电阻率大于1×1013Ωm、介电常数小于10、介电损耗小于3×10-3的氮化硅陶瓷.     

YAG引入方式对碳化硅陶瓷烧结特性、力学性能及结构的影响

采用溶胶-凝胶法和机械共混法分别引入烧结助剂YAG(Y3Al5O12)和Al2O3 Y2O3制备复合粉体,经过无压液相烧结制备碳化硅陶瓷材料,分析了烧结助剂引入方式对碳化硅陶瓷烧结、性能及结构的影响机制.研究结果表明,在1 950℃烧结45 min时,机械共混法制备的复合粉体可以获得较好的烧结性能,陶瓷具有较好的力学性能和显微结构,而溶胶-凝胶法制备的复合粉体则存在过烧.经烧结工艺优化,溶胶-凝胶法制备的复合粉体在1 860℃烧结1 h后,陶瓷可以获得更优的烧结性能、力学性能及更理想的显微结构.复合粉体中YAG相的提前形成及均匀分布促进复合粉体的快速致密,降低烧结温度,改善陶瓷的力学性能及显微结构.细晶、裂纹偏转和晶粒桥联是碳化硅陶瓷的主要增韧机制.     

改良固相法制备透明YAG陶瓷的研究

以高纯氧化铝(Al2O3)、氧化钇(Y2O3)为原料,使用卧式搅拌磨,系统研究了一种制备YAG粉体的改良固相法工艺。该工艺利用高达2000r/min的转速以及直径0.5mm的高纯氧化铝球球磨介质实现了Al2O3、Y2O3粉体亚微米级的均匀混合,可在1350℃实现两种粉体的固相反应,并完全转化为纯YAG粉体,大幅度地降低了YAG的转相温度。作者还初步研究了该粉体的烧结性能,成功制得了透明的YAG陶瓷。     

Al2O3基多元纳米复相陶瓷的制备及其超塑性

采用溶胶-凝胶法制备了Al2O3-ZrO2（3Y）-Spinel纳米复合粉体，其颗粒大小为20-30nm，粒度分布均匀，无硬团聚。采用真空热压烧结工艺制备了纳米复相陶瓷，结果表明：由于纳米复合粉体中的第二相阻止了基体Al2O3的致密化，纳米复合粉体的烧结温度较普通微米粉体相比并没有大幅度降低，其合适的烧结温度为1450～1500℃。烧结体的超塑性压缩试验表明：在1500℃材料表现出良好的超塑变形能力，变形抗力小于30MPa。在整个压缩变形过程中，材料没有出现明显的应变软化，显示出与超塑性拉伸变形截然不同的特性。     

Y2O3对反应烧结Si3N4/SiC复相陶瓷组织和性能的影响

以低压铸造用升液管为研究目的,以Y2O3-Al2O3-Fe2O3为复合烧结助剂,磨切单晶硅废料Si粉和SiC为主料,反应烧结法制备Si3N4/SiC复相陶瓷。研究了Y2O3含量对复合材料结构和力学性能的影响,采用XRD、SEM对复合材料的相组成、微观形貌进行分析。结果表明,反应烧结后试样生成Si3N4结合SiC晶粒为主相的烧结体,并含有少量Sialon晶须及未反应的Si。Y2O3含量对复相陶瓷力学性能影响很大,在分析稀土Y2O3作用机理的基础上,得到2.5%Y2O3优化试样的力学性能优良,相对密度达到88%,维氏硬度达到1.1 GPa,常温抗弯强度50 MPa。     

CeO2,Dy2O3,Yb2O3及Y2O3烧结助剂对氮化硅陶瓷热导率的影响

研究了CeO2-MgO(CeM),Dy2O3-MgO(DyM),Yb2O3-MgO(YbM)及Y2O3-MgO(YM)体系烧结助剂对氮化硅陶瓷的热导率及电学性能的影响.结果表明与YM烧结助剂相比,添加DyM烧结助剂的氮化硅陶瓷热导率较低;添加CeM烧结助剂的氮化硅陶瓷的热导率最高,为85.4W/m·K;添加YbM烧结助剂的氮化硅陶瓷也有较高的热导率,但体电阻率较低.组织分析表明,添加不同稀土元素的烧结体组织形貌基本相同,晶界相不同,添加DyM,YbM和YM烧结助剂的氮化硅陶瓷在烧结过程中分别形成了含氧晶界相Dy2Si3N4O3,Yb2Si3N2O5和Y2Si3N3O4.     

微波烧结制备Y_(1.8)La_(0.2)O_3透明陶瓷

以Y2O3(4N)和La2O3(3N)为原料,采用化学共沉淀方法制备Y1.8La0.2O3粉体,粉体压制后氢气氛下分别采用常规烧结和微波烧结制备Y1.8La0.2O3透明陶瓷。结果表明:900℃煅烧2 h制备的粉体近似球形,粒径约40~60 nm,采用氢气氛下1450℃微波烧结30 min下,可以获得致密性较高、晶粒细小、韧性好、透光率较高的Y1.8La0.2O3透明陶瓷。与常规气氛烧结相比,微波气氛烧结温度明显降低,时间显著减少,且晶粒更细小,其断裂形式由常规烧结时的沿晶断裂逐步过渡到穿晶断裂。     

Al2O3基复相陶瓷共沉淀-水热法制备研究

用共沉淀-水热法制备Ni/ZrO2/Al2O3复相陶瓷粉体,并对烧结体的力学性能和显微形貌进行了讨论.复相粉体的表征采用高分辩透射电镜(HRTEM)和X射线衍射(XRD)等技术.结果表明:在1.4-丁二醇介质中300℃水热条件下自生压高压釜中反应12h成功制备了Ni/ZrO2/Al2O3复合陶瓷粉体,并且测得复相陶瓷体积密度和断裂韧性.通过场发射扫描电镜观察得到烧结体中t-ZrO2颗粒和Ni颗粒的平均尺寸.     

包裹和热压制备Al2O3/Cu复合材料及性能研究

采用非匀相沉淀法制备了纳米Cu包裹Al2O3复合粉体,并利用热压烧结制备出Al2O3/Cu复合材料.利用X-ray衍射(XRD)、热重/差式-量热扫描法(TG/DSC)、透射电镜(TEM)对复合粉体的成分、热学特性以及形貌特征进行了表征;利用扫描电镜(SEM)、显维硬度计及万能试验机测试分析了复合材料的微观结构及力学性能.结果表明,利用非匀相沉淀法可以得到Cu包裹Al2O3的纳米复合粉体,包裹层为非连续态的纳米Cu颗粒,颗粒呈球形,尺寸为10nm左右.同单相Al2O3陶瓷相比,Al2O3/Cu复合陶瓷的力学性能有显著提高,断裂韧性是单相Al2O3陶瓷的1.5倍,复合陶瓷的抗弯强度比单相Al2O3陶瓷提高,且数值离散性下降.     

Al2O3/Al2(1-0.2)Mg0.2Ti(1+0.2)O5基复相陶瓷的制备及其性能

以工业级α-Al2O3、金红石型TiO2和轻质MgO粉体为原料,过量配置α-Al2O3,采用固相反应法于1400℃煅烧实现了Al2O2/Al2(1-0.2)Mgg0.2Ti(1+0.2)O5基复相粉体的原位合成,实现两相的均匀混合,原位制备出性能良好的Al2O3/Al2(1-0.2)Mg0.2Ti(1+0.2)O5基复相陶瓷.利用XRD对原位合成的复相陶瓷粉体的相组成进行了表征,利用FESEM观察了复相陶瓷的断口形貌,测量了复相陶瓷的烧结密度、抗弯强度和热膨胀系数,研究了第二相Al2O3的引入量对钛酸铝基陶瓷的微观结构、抗弯强度和热膨胀性能的影响.结果显示,当复相Al2O3的引入量为15%(质量分数)时,钛酸铝基复相陶瓷的抗弯强度提高到108 MPa,并且具有较低地热膨胀系数0.7×10-6 /℃.     

稀土盐浸泡镁合金微弧氧化膜层的制备及性能(英文)

在 K2ZrF6-Na2SiO3电解液中对 Y(NO3)3浸泡预处理的 AZ91D 镁合金进行微弧氧化处理,在镁合金表面制备 Y2O3-ZrO2-MgO 复合膜层(YSZ-MgO 膜)。运用电子显微镜(SEM)、能谱分析(EDX)、X 射线衍射(XRD)和电化学分析与高温氧化等方法研究 YSZ-MgO 膜的组成与结构、耐腐蚀性及热稳定性。结果表明,YSZ-MgO 膜主要由 Y2O3、ZrO2、MgO 和 Mg2SiO4等物相组成,和未经 Y(NO3)3浸泡的膜层(ZrO2-MgO 膜)相比,YSZ-MgO膜的厚度较小,但膜层的致密性较好,表面粗糙度较小;且腐蚀电流密度较小、开路电位较正、极化阻抗较高;在 5%NaCl 溶液中的腐蚀速率低于 ZrO2-MgO 膜的,约为 AZ91D 镁合金的 8%。YSZ-MgO 膜层比普通 ZrO2-MgO膜层具有更强的抗高温氧化性能和耐热冲击性能。     

Effects of adding yttrium nitrate on the mechanical properties of hot-pressed AlN ceramics

Aluminum nitride (AlN) ceramics were prepared by hot-pressing with Y(NO₃)₃·6H₂O as sintering additive. The mechanical properties including flexural strength, Vickers’ hardness, and fracture toughness were studied. The relative density and mechanical property of the monolithic AlN were improved by adding Y(NO₃)₃·6H₂O, which decreased the porosity. At 2 wt% Y₂O₃, the AlN ceramic exhibited the highest strength of 383 MPa, the highest hardness of 15.39 GPa, and the highest fracture toughness of 3.1 MPa m^1/2. However, doping with more additive, the strength, hardness, and toughness of AlN ceramics decreased because of the weak interfacial bonding between AlN matrix and the yttrium aluminates phase.     

Y_2O_3/Ag复合材料的制备与性能

选择了粒度为～0.91μm的Y2O3微粉作为添加剂,通过粉末冶金的方法制备了不同Y2O3含量的Ag基复合材料,并测试了样品的力学性能和硬度。结果证明,相同制备条件下,与纯Ag相比,2%Y2O3/Ag基复合材料的抗拉强度提高了约24%。当Y2O3质量分数为1.2%时,Y2O3/Ag基复合材料的抗拉强度和硬度达到最大。扫描电镜和能谱分析结果表明,在Ag基体中存在碳,Y2O3颗粒发生了团聚。     

机械合金化与热压烧结法制备2Si-B-3C-N陶瓷

以Si_3N_4、B4C、C、Si等粉末为原料,采用机械合金化方法制备2Si-B-3C-N粉末,在氮气保护下1900 ℃, 40 Mpa热压烧结30 min获得2Si-B-3C-N陶瓷,研究了块体陶瓷微观组织结构与力学性能.高能球磨粉末在热压烧结后致密度达到了97.9%.热压烧结的2Si-B-3C-N陶瓷中主要含有等轴状的b-SiC和层片状的h-BCN相.BCN晶粒尺寸约为200 nm,SiC晶粒尺寸约为400～500 nm.BCN晶粒主要分布在SiC晶粒周围.2Si-B-3C-N陶瓷的室温抗弯强度、弹性模量、断裂韧性、硬度分别为446.6 Mpa、144.6 Gpa、5.10 Mpa×m~(1/2)和5.53 Gpa.在高温空气状态下,2Si-B-3C-N陶瓷的抗弯强度随温度的升高而降低,1000和1400 ℃下的抗弯强度分别为358.7和202.1 Mpa.     

Fabrication of nanocrystalline WC and nanocomposite WC–MgO refractory materials at room temperature

Reactant material powders of pure WO₃, Mg and graphite have been milled at room temperature using a high-energy ball mill. After a few kiloseconds of milling (11 ks), numerous fresh surfaces of the reactant materials are created as a result of the repeated impact and shear forces generated by the balls. After 86 ks of milling, a mechanical solid state reduction is successfully achieved between the fresh Mg and WO₃ particles to form a product of nanocrystalline mixture of MgO and W. A typical mechanical solid state reaction takes place between the W particles and graphite powders to obtain fine grains of nanocrystalline WC. Towards the end-stage of ball-milling (173 ks), the nanocrystalline MgO grains (10 nm) are embedded into the fine matrix of WC to form fine nanocomposite powders (1 μm in diameter) of WC–18% MgO material with spherical-like morphology. This composite powder was then consolidated under vacuum at 1963 K, with a pressure ranging from 19.6 to 38.2 MPa for 0.3 ks, using a plasma activated sintering method. In addition, pure nanocrystalline WC powders (7 nm in diameter) obtained by removing the MgO from the milled powders, using a simple leaching technique have been also consolidated by the same consolidation technique. The consolidation step does not lead to a dramatic grain growth and the compacted samples that are fully dense still maintain their unique nanocrystalline characteristics. The elastic properties and the hardness of both consolidated samples have been investigated. A model for fabrication of refractory nanocrystalline WC and nanocomposite WC–18% MgO materials at room temperature is proposed.     

热压烧结温度对两种金属陶瓷组织性能的影响

金属陶瓷材料具有高硬度、高热稳定性和高耐磨性,提高金属陶瓷材料断裂强度和断裂韧性具有重要应用意义。本文采用粉末冶金热压烧结方法制备了Al2O3+Ti(C,N)和Al2O3+WC两种金属陶瓷材料。通过单边切口梁(SENB)法和三点弯曲等力学性能测试方法探讨了热压温度对两种金属陶瓷材料的力学性能的影响,利用X射线衍射、扫描电镜(SEM)分析了物相组成和断口显微结构。实验结果表明:Al2O3+Ti(C,N)金属陶瓷随着烧结温度的升高,力学性能升高。而Al2O3+WC金属陶瓷随着烧结温度的升高,力学性能下降,在1400℃、10MPa烧结保温15min下力学性能较好。Al2O3+WC金属陶瓷900℃热压缩断裂强度比1000℃热压缩断裂强度高。     

纳米压入技术表征薄膜（涂层）的力学性能

采用纳米压入技术测试薄膜（涂层）的力学性能日益受到关注。测试过程中可自动记录载荷－压深曲线,能够获取薄膜（涂层）的硬度、弹性模量、薄膜（涂层）自身结合强度、膜基界面结合强度、残留应力、屈服强度以及应变硬化率等力学性能数据。本文扼要介绍了纳米压入技术表征薄膜（涂层）力学性能的测试原理。     

Consolidation of Al2O3/Al Nanocomposite Powder by Cold Spray

While the improvement in mechanical properties of nanocomposites makes them attractive materials for structural applications, their processing still presents significant challenges. In this article, cold spray was used to consolidate milled Al and Al₂O₃/Al nanocomposite powders as well as the initial unmilled and unreinforced Al powder. The microstructure and nanohardness of the feedstock powders as well as those of the resulting coatings were compared. The results show that the large increase in hardness of the Al powder after mechanical milling is preserved after cold spraying. Good quality coating with low porosity is obtained from milled Al. However, the addition of Al₂O₃ to the Al powder during milling decreases the powder and coating nanohardness. This lower hardness is attributed to non-optimized milling parameters leading to cracked particles with insufficient Al₂O₃ embedding in Al. The coating produced from the milled Al₂O₃/Al mixture also showed lower particle cohesion and higher amount of porosity.     

Preparation of transparent yttrium aluminum garnet ceramics by relatively low temperature solid-state reaction

1　INTRODUCTIONYttriumaluminum garnet(YAG )isakindofcomplexoxideresultedfromthereactionofY2 O3andAl2 O3.ItschemicalformulaisY3Al5O12 .Ithasagarnetcrystalstructureandbelongstohexagonalsys tem .YAGceramicsholdpromiseforcertainopticalapplicationssuchashightemperaturewindowsusedtodetectinfraredwavesordevicesusedtorecordnu clearradiation .Becauseofitsthermalstability ,highhardness,physicalandchemicalstability ,andexcel lenttransparencyinawidewavelengthregionfromvisiblelighttoinfraredlight…