晶内型Al2O3—SiC纳米复合陶瓷的制备

研究了沉淀法制备Ａｌ２Ｏ３－ＳｉＣ纳米复合陶瓷的工艺过程，利用Ａｌ２Ｏ３从γ相到α相的蠕虫状生长过程，使大部分纳米ＳｉＣ颗粒位于Ａｌ２Ｏ３晶粒内，用沉淀法制得的、含有５ｖｏｌ％ＳｉＣ的Ａｌ２Ｏ３－ＳｉＣ纳米复合陶瓷，其强度为４６７ＭＰａ，韧性为４．７ＭＰａ．ｍ＾１／２，与一般的Ａｌ２Ｏ３陶瓷相比有较大的提高，显示了沉淀法制备Ａｌ２Ｏ３－ＳｉＣ纳米复合陶瓷的优点。     

Si3N4／SiC纳米复合陶瓷的制备,结构和性能

Ｓｉ３Ｎ４／ＳｉＣＵ纳米复合陶瓷是近年发展起来的高温高温度结构材料，它通过纳米ＳｉＣ颗粒在Ｓｉ３Ｎ４基体中的弥散达到强化增韧的效果。研究表明，这种增韧方法所获得的室温和高温机械性能均远远高于其它的增韧方法。本文综述了Ｓｉ３Ｎ４／ＳｉＣ纳米复合陶瓷在制备、结构和性能方面的研究成果，指出了尚待解决的问题和今后的研究方向。     

Sialon,Al2O3和SiC自配对干摩擦研究

本文研究了高温结构陶瓷Ｓｉａｌｏｎ、Ａｌ２Ｏ３、ＳｉＣ的自配对滑动干摩擦磨损性能，运用ＳＥＭ、ＴＥＭ、ＸＰＳ手段观察和分析了磨损面的表面形貌、磨屑形状及相组成，目的是揭示陶瓷材料在试验条件下的滑动干摩擦磨损规律和摩擦磨损机理，结果表明：Ｓｉａｌｏｎ$ 微剥离磨损，摩擦过程中产生的氧化产物能改善材料摩擦；Ａｌ２Ｏ的磨损机理是磨屑边界润滑下的晶粒拔出和沿晶断裂；ＳｉＣ表现为犁沟－磨屑－犁沟过程的磨损，并     

纳米SiC—Si3N4复合粉体的制备及研究

本文以炭黑和气凝氧化硅为原料，采用碳热还原氮化的方法制备纳米ＳｉＣ－Ｓｉ３Ｎ４复合粉体；复合粉中ＳｉＣ的含量由起始粉中Ｃ：ＳｉＯ２的摩尔比控制。在复合粉体的表征中用ＸＲＤ线宽法测量ＳｉＣ粒径大小。ＴＥＭ照片显示Ｓｉ３Ｎ４粒径在１００￣２００ｎｍ；ＳｉＣ为纳米级。文中还对生成复合粉体的反应机理进行了探讨。同时利用这一工艺制备出单相的Ｓｉ３Ｎ４粉和ＳｉＣ粉。     

Si3N4／SiC纳米复合陶瓷的微观结构

利用ＪＥＭ２０００ＥＸⅡ高分辨电镜和ＨＦ２０００冷场发射枪透射电镜对Ｓｉ３Ｎ４ＳｉＣ纳米笔合陶瓷材料的微观组织，结构和成分进行了研究。结果表明，ＳｉＣ颗粒弥散分布基体相β－Ｓｉ３Ｎ４晶内和晶界，晶内ＳｉＣ颗粒与基体相的界面结构有三种类型；１）直接结合的的界面；２）完全非晶态的界面；３）混合型的界面，晶间ＳｉＣ颗粒与基体相的界面大部分是直接结合的。     

SiC陶瓷的冲蚀磨损耐磨性

研究了无压（ＰＬ），热压（ＨＰ）、热等静压（ＨＩＰ）烧结ＳｉＣ陶瓷的室温冲蚀磨损行为。热等静压ＳｉＣ陶瓷具有良好的综合力学性能和细致的组织结构，其冲蚀磨损耐磨性比无压的热压烧结ＳｉＣ陶瓷要好。     

热等静压Al2O3／SiC和SiCw／SiC陶瓷磨粒磨损行为的比较研究

通过ＳＥＭ观察和ＥＤＸＡ分析对Ａｌ２Ｏ３／ＳｉＣ和ＳｉＣｗ／ＳｉＣ陶瓷的耐磨粒磨损性进行了比较研究。在低应力下，Ａｌ２Ｏ３／ＳｉＣ陶瓷的耐磨性优于ＳｉＣｗ／ＳｉＣ陶瓷，而在较高应力下则相反。     

SiC／Al合金层状复合材料的机械性能及损伤行为

在室温条件下测定了Ａｌ合金以连续层状形式存在于ＳｉＣ陶瓷层间并渗透入ＳｉＣ陶瓷层内、Ａｌ合金浓度呈层状变化高低相间，以及Ａｌ合金和ＳｉＣ陶瓷均匀分布相互渗透三种ＳｉＣ含量相同而结构形式不同的ＳｉＣ／Ａｌ合金复合材料的机械性能；用ＳＥＭ和光学显微镜观察分析了复合材料的断口形貌及裂纹扩展过程。结果表明，在ＳｉＣ陶瓷层间以连续层状形式存在的Ａｌ合金在应力作用下发生较大程度的塑性变形，在裂纹尾部被拉伸和形成桥接，引起能量耗散，减缓裂纹扩展速度，防止裂纹张开，使复合材料的韧性得到明显改善；ＳｉＣ／Ａｌ合金陶瓷─金属层状复合材料的损伤形式主要是ＳｉＣ陶瓷层开裂、金属层桥接和裂纹偏转。     

Ca—α—Sialon／SiC纳米相复合材料

本文通过反应热压压制备了Ｃａ－α－Ｓｉａｌｏｎ／ＳｉＣ纳米相复合材料。显微结构研究表明，α－Ｓｉａｌｏｎ（α＇）晶粒细小，成等轴状；ＳｉＣ颗粒直径在５０￣１５０ｎｍ左右，颗粒较大的分布于α＇三晶粒的交叉处，颗粒较小的可以被包裹在α－Ｓｉａｌｏｎ的晶粒内部。纳米相ＳｉＣ的加入对裂纹扩懈具有较大的阻碍作用，从而强化晶界，使材料的强度和硬度都有明显提高。     

反应烧结TiB2—SiC复相陶瓷的物相反应,力学性能及残余应力

利用ＴｉＨ２，Ｓｉ和Ｂ４Ｃ之间的化学反应制备ＴｉＢ２－ＳｉＣ复相陶瓷，研究了反应时物相生成机理及添加Ｎｉ对材料力学性能的影响，采用ＳＥＭ观察复相陶瓷的显微结构及裂纹扩展过程，用ＸＲＤ法测定了复相陶瓷内的残余应力，探讨了复相陶瓷的增韧机理，同时，残余应力测试结果表明，精磨会给材料表面带来一定的机械加工应力，但随方向而异、并对残余应力的测定造成影响。     

Analyses of the role of grain boundaries in mesoscale dynamic fracture resistance of SiC-Si3N4 intergranular nanocomposites

Silicon carbide (SiC)-silicon nitride (Si₃N₄) nanocomposites with SiC dispersions as well as Si₃N₄ matrix of mesoscale dimensions (∼1 μm) are considered to have exceptional strength attributed to interactions of SiC dispersions with Si₃N₄ grain boundaries (GBs). However, an account of GBs on the strength of these nanocomposites is not available. In order to analyze this issue, cohesive finite element method (CFEM) based mesoscale dynamic fracture analyses of SiC-Si₃N₄ nanocomposites with an explicit account of length scales associated with Si₃N₄ GBs, SiC particles, and Si₃N₄ grains are performed. Analyses indicate that primary mechanism of fracture in the nanocomposite microstructures is intergranular Si₃N₄ matrix cracking. GBs are responsible for crack deflection and accordingly damage is limited to a smaller geometric region in microstructures with GBs. On an average, a microstructure with GBs present is stronger than the corresponding microstructure with GBs removed. However, in cases where the second phase SiC particles are in the wake of microcracks the microstructure without GB becomes stronger against fracture in comparison to the corresponding one with GBs owing to the crack bridging effect caused by the second phase SiC particles.     

原位生成TiC/Ti5Si3纳米复合材料的显微结构研究

研究了原位生成ＴｉＣ／ＴＩ５Ｓｉ３纳米复合材料的显微结构,实验结果表明,以ＳｉＣ和Ｔｉ原料,通过反应热压工艺可以原位合成ＴｉＣ／Ｔｉ５Ｓｉ２复合材料,其中的大部分ＴｉＣ粒子为纳米粒子,ＴｉＣ晶粒与Ｔｉ５Ｓｉ３晶粒的晶界上存在原子台阶,复合材料还含有少量Ｔｉ３ＳｉＣ２相,这些Ｔｉ３ＳｉＣ２相主要呈棒状分布在Ｔｉ５Ｓｉ３基体中,另有少量ＴｉｅＳｉＣ２相位震大的ＴｉＣ晶粒内。     

反应熔渗法制备纳米 MoSi2-SiC复合材料

运用Mo＋C坯体反应溶渗法，可以得到MoSi2-SiC复合材料，其基体相晶粒尺寸为150-600nm，反应生成的SiC相分布均匀，大小为30-160nm之间．该纳米MoSi2-SiC复合材料强度为214．8MPa，断裂韧性为4．1MPa·m^1／2，力学性能远高于单相材料．透射电镜研究表明，在复合材料中存在大量的层错和一些位错，也有孪晶存在．     

Interfacial microstructure of Si3N4/Si3N4 brazing joint with Cu–Zn–Ti filler alloy

In this study, Si₃N₄ ceramic was jointed by a brazing technique with a Cu–Zn–Ti filler alloy. The interfacial microstructure between Si₃N₄ ceramic and filler alloy in the Si₃N₄/Si₃N₄ joint was observed and analyzed by using electron-probe microanalysis, X-ray diffraction and transmission electron microscopy. The results indicate that there are two reaction layers at the ceramic/filler interface in the joint, which was obtained by brazing at a temperature and holding time of 1223 K and 15 min, respectively. The layer nearby the Si₃N₄ ceramic is a TiN layer with an average grain size of 100 nm, and the layer nearby the filler alloy is a Ti₅Si₃N_x layer with an average grain size of 1–2 μm. Thickness of the TiN and Ti₅Si₃N_x layers is about 1 μm and 10 μm, respectively. The formation mechanism of the reaction layers was discussed. A model showing the microstructure from Si₃N₄ ceramic to filler alloy in the Si₃N₄/Si₃N₄ joint was provided as: Si₃N₄ ceramic/TiN reaction layer/Ti₅Si₃N_x reaction layer/Cu–Zn solution.     

Fabrication,mechanical properties and microstructure analysis of Si3N4/SiC nanocomposite

Ceramic nanocomposites, Si₃N₄ matrix reinforced with nano-sized SiC particles, were fabricated by hot pressing the mixture of Si₃N₄ and SiC fine powders with different sintering additives. Distinguishable increase in fracture strength at low and high temperatures was obtained by adding nano-sized SiC particles in Si₃N₄ with Al₂O₃ and/or Y₂O₃. Si₃N₄/SiC nanocomposite added with Al₂O₃ and Y₂O₃ demonstrated the maximum strength of 1.9 GPa with average strength of 1.7 GPa. Fracture strength of room temperature was retained up to 1400 as 1 GPa in the sample with addition of 30 nm SiC and 4 wt% Y₂O₃. Striking observation in this nanocomposite is that SiC particles at grain boundary are directly bonded to Si₃N₄ grain without glassy phases. Thus, significant improvement in high temperature strength in this nanocomposite can be attributed to inhibition of grain boundary sliding and cavity formation primarily by intergranular SiC particles, besides crystallization of grain boundary phase.     

溶胶-凝胶法制备纳米Si3N4(Y2O3)粉末的研究

本文以硅溶胶、尿素和炭黑为原料，采用溶胶－凝胶碳热氮化法在１５００℃、２ｈ条件下制得粒径为５０－８０ｎｍ的Ｓｉ３Ｎ４纳米粉末。比较了由硅溶胶与尿素经氨解合成的前驱体和硅溶胶二种不同起始物料的反应活性，研究了氮化条件对合成反应的影响。结果表明：氨解前驱体使硅溶胶中的结构水排除，有助于加快反应速率，提高产物氮含量。本文同时以Ｙ（ＮＯ３）３为添加剂，在溶液状态与硅源混合，合成了Ｓｉ３Ｎ４－Ｙ２Ｏ３纳米复     

Fabrication and mechanical properties of silicon carbide–silicon nitride nanocomposites

A powder mixture of ultrafine –SiC–35 wt% –Si₃N₄ containing 6 wt% Al₂O₃ and 4 wt% Y₂O₃ as sintering additives were liquid–phase sintered at 1800°C for 30 min by hot–pressing. The hot–pressed composites were subsequently annealed at 1920°C under nitrogen–gas–pressure to enhance grain growth. The average grain–size of the sintered bodies were ranged from 96 to 251 nm for SiC and from 202 to 407 nm for Si₃N₄, which were much finer than those of ordinary sintered SiC–Si₃N₄ composites. Both strength and fracture toughness of fine–grained SiC–Si₃N₄ composites increased with increasing grain size. Such results suggested that a small amount of grain growth in the fine–grained region (250 nm for SiC and 400 nm for Si₃N₄) was beneficial for mechanical properties of the composites. The room–temperature flexural strength and fracture toughness of the 8–h annealed composites were 698 MPa and 4.7 MPa · m^1/2, respectively.     

Large electrical resistivity and high saturation magnetization nanocrystalline Fe86B13Cu1 alloy prepared by hot isothermal pressing

The effects of hot isothermal pressing (HIP) on the microstructures and magnetic properties of nanocrystalline Fe₈₆B₁₃Cu₁ ribbons were studied. It is shown that the precipitation of Fe₃B phase is suppressed and the grain size of α-Fe phase decreases to 13.2 nm when amorphous Fe₈₆B₁₃Cu₁ ribbons are annealed by HIP under the pressure of 150 MPa. A high electrical resistivity and high saturation magnetization nanocrystalline soft magnetic material is prepared by HIP owing to the suppression of the precipitation of Fe₃B phase and a marked decrease in the grain size of α-Fe phase. The prepared sample exhibits a large electrical resistivity of 183 μΩ cm, a high saturation magnetization of 1.94 T and a low coercive force of 12 A/m.     

Mechanical properties and microstructure in sintered and HIPed SiC particle/Si3N4 composites

Pressureless sintered (PLS) and gas-pressure sintered (GPS) Si₃N₄, PLS and GPS SiC particle/Si₃N₄ composites, and PLS + HIP and GPS + HIP SiC particle/Si₃N₄ composites were produced. Investigation of their mechanical properties showed that PLS + HIP and GPS + HIP composites, containing SiC particles in the beta-silicon nitride grains, yield higher bending strength, although its fracture toughness remains at the same level. This is attributed to the fact that the added SiC particles inhibit excessive growth of beta-Si₃N₄ grains without changing the fracture behaviour. However, this investigation also found precipitation during the reaction between SiC and nitrogen in gas pressure sintering, resulting in a low Young's modulus and low density in the GPS composite.