SiC/Fe-Cr合金界面反应的研究

使用ＸＲＤ、ＥＭＰＡ和 ＳＥＭ等对 ９００～１１５０℃高温处理后的ＳｉＣ／Ｆｅ－２０Ｃｒ合金界面反应区的显微结构和反应动力学进行了研究．界面反应区分为ＳｉＣ反应区和金属反应区两部分：ＳｉＣ反应区由组成为Ｆｅ_３Ｓｉ、Ｃｒ_３Ｓｉ和Ｃｒ_７Ｃ_３的白亮基体和其间随机分布的细小石墨颗粒构成;金后反应区则是一个由（Ｃｒ;Ｆｅ）_７Ｃ_３构成的均匀组织。ＳｉＣ／Ｆｅ－２０Ｃｒ合金界面反应为扩散控制,反应动力学方程为 Ｋ＝１．９×１０^－４ｅｘｐ（(－２３５×１０^３)／ＲＴ）ｍ^２·ｓ^－１．金属反应区介于ＳｉＣ反应区和合金之间,阻挡合金中的Ｆｅ原子通过它向ＳｉＣ反应区中扩散,抑制界面反应,这种作用随合金中Ｃｒ含量的增加而加强．     

SiC－AlN－Y_2O_3复相陶瓷的氧化行为

经研究致密的ＳｉＣ－ＡｌＮ－Ｙ２Ｏ３复相陶瓷的氧化行为后发现，陶瓷材料的表面在空气中氧化的反应物随着温度的高低而变化．８００℃、２０ｈ氧化试验后，试样表面无任何变化，１１００℃氧化．２０ｈ，表面形成了极少量的ＳｉＯ２，但两者均无增重．１２５０℃与１３２０℃氧化３０ｈ后，试样的重量和表面发生较明显的变化，形成了ＳｉＯ２与α－Ａｌ２Ｏ３，１３７０℃氧化试验３０ｈ后，陶瓷表面的氧化产物ＳｉＯ２与α－Ａｌ２Ｏ３转化成莫来石（３Ａｌ２Ｏ３·２ＳｉＯ２）结构．试样表面的氧化层均匀而且致密．     

Al／SiC复合材料界面反应的DTA研究

本文以多层膜模拟复合材料界面反应，用ＤＴＡ及ＸＲＤ研究了ＴｉＣ，Ａｌ２Ｏ３和ＳｉＯ２作为Ａｌ／ＳｉＣ体系的反应阻挡层的作用．发现经７００℃，１ｈ处理后，Ａｌ２Ｏ３不与Ａｌ或ＳｉＣ反应，有很好的阻挡作用；ＴｉＣ与Ａｌ反应生成ＴｉＡｌ３后也能阻止Ａｌ与ＳｉＣ的反应；ＳｉＯ２与Ａｌ反应，导致一定数量的Ｓｉ溶入Ａｌ中，是否起阻挡作用有待进一步分析．     

Ni42Cr6Fe封接合金氧化膜和氧化物晶须的结构

用ＴＥＭ、Ｘ－Ｒａｙ、ＳＥＭ等技术研究了Ｎｉ４２Ｃｒ６Ｆｅ玻封合金在高温湿Ｈ２中形成的氧化膜及氧化物晶须的结构。结果表明：氧化膜主要由Ｃｒ２Ｏ３和（Ｆｅ，Ｍｎ）Ｃｒ２Ｏ４两组相成，氧化膜底层是以Ｃｒ２Ｏ３为主的组织，氧化膜表层是以（Ｆｅ，Ｍｎ）Ｃｒ２Ｏ４为主的组织；Ｓｉ在氧化膜与合金界面分布，Ａｌ则在内氧化层中形成内氧化物质点；氧化膜表面生长的氧化物晶须的杆部为（Ｆｅ，Ｍｎ）Ｃｒ２Ｏ４单晶，头部为     

SiC纤维补强微晶玻璃基复合材料的界面结合

本文通过ＳｉＣ纤维对ＬＣＡＳ（Ｌｉ２Ｏ－ＣａＯ－Ａｌ２Ｏ３－ＳｉＯ２）和ＭＡＳ（ＭｇＯ－Ａｌ２Ｏ３－ＳｉＯ２）微晶玻璃的补强，观察和分析了在不同复合系统中纤维与基体的界面结合。在ＳｉＣ纤维／ＬＣＡＳ微晶玻璃复合系统中，发现纤维与基体之间有一中间界面层，它主要是在复合材料的烧结过程中通过扩散形成，并且于１２００℃时在界面上形成富Ｃ层。ＳｉＣ纤维／ＭＡＳ微晶玻璃基复合材料由于在烧结过程中有化学反应发生     

SiC－AlN－Y_2O_3复相陶瓷的制备与性能

通过热压烧结技术，ＳｉＣ、ＡｌＮ和Ｙ２Ｏ３粉末混合作在１９２０～２０５０℃、Ａｒ气氛下形成了致密的复相陶瓷．在室温下ＳｉＣ－ＡｌＮ－Ｙ２Ｏ３复相材料的抗弯强度和断裂韧性分别达到６００ＭＰａ和７ＭＰａ·ｍ１／２以上运用ＸＲＤ、ＳＥＭ和ＴＥＭ分析致密样品的断裂裂纹、形貌和组成．ＳｉＣ－ＡｌＮ－Ｙ２Ｏ３复相陶瓷在１３７０℃氧化试验３０ｈ，其氧化产物为莫来石．     

Si／SiC材料900℃时的氧化

研究了反应烧结碳化硅（Ｓｉ／ＳｉＣ）材料在９００℃时的氧化过程及添加Ｎｉ、Ａｌ元素对其氧化过程的影响。结果表明,Ｓｉ／ＳｉＣ材料的氧化过程遵循抛物线规律,并在Ｓｉ／ＳｉＣ材料氧化表面出现针状ＳｉＯ２。Ｓｉ／ＳｉＣ中添加Ｎｉ、Ａｌ元素后,氧化表面比较光滑,针状ＳｉＯ２消失,从而提高了其抗氧化能力。     

Cr／SiO2界面还原反应研究

利用俄歇电子能谱研究了Ｃｒ／ＳｉＯ２薄膜在热处理过程中的界面扩散反应机理、界面反应动力学过程及界面反庆产物。研究结果表明，Ｃｒ／ＳｉＯ２体系的界面还原反应主要是Ｃｒ与Ｓｉ２的反应，其还原反应产物是ＣｒＳｉ和Ｃｒ２Ｏ２物种。界面还原反 速度与反应时间的平方根成正比，其界面还原反应过程受Ｃｒ向Ｓｉ２层的扩散过程所控制，界面还原反应的表观活化能力为７２．５ｋＪ／ｍｏｌ（约０．７５ｅＶ）。     

PZT／Si薄膜的扩散反应研究

运用ＸＰＳ和ＡＥＳ研究了ＰＺＴ膜／Ｓｉ在热处理过程中的薄膜及界面化学反应；在热处理过程中，气氛中的气通过ＰＺＴ的缺陷通道扩散到ＰＺＴ／Ｓｉ同旧，并与界面上的硅发生氧化反应形成ＳｉＯ２界面层。同时基底上的硅通过ＰＺＴ的缺陷扩散么样品表面形成ＳｉＯ２表面层。此外，在ＰＺＴ／Ｓｉ界面上，Ｔｉ的氧化物和Ｓｉ发生还原反应，形成了ＴｉＳｉｘ金属硅化物，并残留在ＰＺＴ膜层和和ＳｉＯ２界面层中。在ＰＺＴ膜层内，有     

SiC—AlN—Y2O3复相陶瓷的制备与性能

通过热压烧结技术，ＳｉＣ、ＡｌＮ和Ｙ２Ｏ３粉末混合体在１９２０￣２０５０℃、Ａｒ气氛下形成了致密的复相陶瓷。在室温下ＳｉＣ－ＡｌＮ－Ｙ２Ｏ３复相材料的抗弯强度和断裂韧性分别达到６００ＭＰａ和７ＭＰａ·ｍ＾１／２以上。运用ＸＲＤ、ＳＥＭ和ＴＥＭ分析致密样品的断裂裂纹、形貌和组成。ＳｉＣ－ＡｌＮ－Ｙ２Ｏ３复相陶瓷在１３７０℃氧化试验３０ｈ，其氧化产物为莫来石。     

CVD SiC涂层SiC纤维增强SiC复合材料的研究

本文采用CVD技术对KD-1 SiC纤维作涂层处理,再通过聚碳硅烷浸渍裂解法制备单向SiCf/SiC复合材料.研究了不同沉积时间的CVDSiC涂层对SiCf/SiC复合材料性能的影响,同时运用SEM研究了SiC纤维表面SiC涂层的形貌.结果表明:经过5小时CVDSiC涂层SiCf/SiC复合材料具有良好的力学性能和抗氧化性能.     

泡沫碳化硅陶瓷表面纳米多孔碳化硅涂层的制备

利用硅改性树脂中硅元素和碳元素分子级均匀分散的特征,以硅改性树脂为涂层原料,在泡沫碳化硅陶瓷表面原位生成了多孔碳化硅活性涂层。在加入适量活性炭颗粒的条件下,在泡沫碳化硅陶瓷表面得到了性能良好的纳米碳化硅涂层,适合作为催化剂载体。相反,在没有活性炭颗粒加入的情况下,所得涂层龟裂、结合强度低,且碳化硅团聚成片,比表面积小。     

Growth of SiC particles in reaction sintered SiC

For reaction sintered SiC (RSSC) prepared at 1600°C by conventional melt infiltration technique, experimentation with two different particle sizes of initial SiC, viz., 0.2 and 23.65 μm, showed that the large SiC particles remained unaltered and the sizes of the fine-grained SiC increased several times yielding well-developed faceted crystals in the final material. To study the process further, compacts of SiC powder of particle sizes varying between 0.20 and 8.99 μm were reacted with pure Si at 1600°C and the resulting SiC–Si boundaries were studied by optical microscopy. A distinct boundary layer with no penetration of Si in the compact of SiC of 0.2 μm was observed and the width of the SiC–Si boundary was found to be increasing linearly with time. Detailed SEM examination establishes the growth of the SiC upto around 4 μm from 0.2 μm starting powder. No such growth was observed in the case of starting SiC powder coarser than 0.2 μm. The growth of SiC is explained in terms of solution-reprecipitation mechanism.     

Long-term strength of SiC fibers with nanocrystalline SiC coatings

The long-term strength σ_t of SiC fibers coated with SiC nanoparticles is approximately equal to30·10 ⁷ pa for t=200h at 1500K. The long-term strength of coated fibers is lower than for fibers without coatings by 25–50%. Owing to their enhanced reaction characteristics, the nanocrystalline SiC coatings are sintered at T<1500K, which is lower than the temperature of sintering of self-bonded SiC by 500 K. For this reason, we can recommend coated SiC fibers for manufacturing SiC/SiC composites by sintering at a temperature of 1500K because, at this temperature, SiC fibers do not degrade. Shevchenko National University, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 1, pp. 95 – 99, January – February, 1998.     

Fatigue behaviour of 3-d SiC/SiC Composites

A tension–tension fatigue damage analysis was performed using 3-d silicon carbide fibre reinforced (orthogonal) silicon carbide matrix (SiC/SiC) composites. Two groups of SiC/SiC specimens were tested. The first group consisted of samples without any oxidation protective top layer coating, whilst the latter one contained samples covered with a well fitting, chemical vapour deposited (CVD) SiC system. This coating is necessary for the material to sustain high temperatures. Both the coated and uncoated material had a fibre volume fraction of about 36% equally distributed in three rectangular directions. Load control fatigue tests were conducted at room temperature. The fatigue life was found to decrease by increasing the cyclic stress level. A power-law equation is proposed, which correlates the applied maximum stress during the fatigue test with the number of cycles to failure. In general, the presence of the coating layer decreases the static strength of the material. However, the nominal maximum cyclic stress for which the endurance fatigue limit appeared, remained unaffected by the presence of the oxidation protective SiC coating. Microstructural examination has also been performed on the fractured specimens and it reveals some of the failure mechanisms of the composite that appeared under quasi-static and dynamic loading.     

Modeling of electromechanical behavior of woven SiC/SiC composites

A coupled electro-mechanical model was developed to predict the mechanical behavior of woven SiC/SiC ceramic matrix composites and electrical resistance response to mechanical damages in the composites. The matrix is explicitly included in the model such that the matrix cracking and fiber break can be linked to the electrical resistance change during loading. The results show that the electrical resistance increases linearly with an increase of matrix crack density and the number of fiber breaks. The predictions are compared to the experimental results on 2D woven SiC/SiC ceramic composites. With proper materials parameters input, the models can accurately predict the stress–strain curve and electrical resistance change during the loading. The model is further compared to an analytical solution of electromechanical coupling to get an insight into the electrical–mechanical interaction mechanisms in the composites.     

不同界面SiC/SiC复合材料的断裂行为研究

碳化硅纤维增强碳化硅复合材料(SiC/SiC)是极具前景的高温结构材料。通过先驱体浸渍裂解(PIP)工艺分别制备了PyC界面和CNTs界面SiC/SiC复合材料, 对两种SiC/SiC复合材料的整体力学性能以及界面剪切强度等进行了测试表征, 并对材料中裂纹的产生与扩展进行了原位观测。结果表明, 两种界面SiC/SiC复合材料弯曲强度相近, 但PyC界面SiC/SiC复合材料的断裂韧性约为CNTs界面SiC/SiC复合材料的两倍。在PyC界面SiC/SiC复合材料中, 裂纹沿纤维-基体界面扩展, PyC涂层能够偏转或阻止裂纹, 材料呈现伪塑性断裂特征; 而在CNTs界面SiC/SiC复合材料中, 裂纹在扩展路径上遇到界面并不偏转, 初始裂纹最终发展为主裂纹, 材料呈现脆性断裂模式。     

SiC及a-SiC：H薄膜的辐照及其进展

SiC是一种宽带隙半导体材料,在高温,高频在,大功率,光电子及抗辐射等方面具有巨大的应用潜力,介绍了国外对该材料及其薄膜进行辐照的一些结果,并指出开展SiC及其薄膜辐照效应研究的重要意义,预测了其发展方向和应用前景。     

Localized mechanical property assessment of SiC/SiC composite materials

SiC fiber-reinforced SiC matrix composites (SiC/SiC) are under consideration as a structural material for a range of nuclear applications. While these materials have been studied for decades, recently new small scale materials testing techniques have emerged which can be used to characterize SiC/SiC materials from a new perspective. In this work cross section nanoindentation was performed on SiC/SiC composites revealing that both the hardness and Young’s modulus was substantially lower in the fiber compared to the matrix despite both being SiC. Using scanning electron microscopy it was observed that the grain growth of the matrix during formation was radially out from the fiber with a changing grain structure as a function of radius from the fiber center. Focused ion beam machining was used to manufacture micro-cantilever samples and evaluate the fracture toughness and fracture strength in the matrix as a function of grain orientation in the matrix. Additionally microstructural characterization techniques like Raman spectroscopy, X-ray diffraction, and microtomography were used to evaluate differences in the matrix and fibers of the composite.