N.C.Si
,
Z.H.Jia
,
L.B.Qi
金属学报(英文版)
Effect of carbon, compound RE, quenching temperature, pre-strain and recovery tem-perature on shape memory effect (SME) of Fe-Mn-Si-Ni-C-RE shape memory alloy was studied by bent measurement, thermal cycle training, SEM etc. It was shown that the grains of alloys addition with compound RE became finer and SME increased evidently. SME of the alloy was weakening gradually as carbon content increased under small strain (3). But in the condition of large strain (more than 6), SME of the alloy whose carbon content range from 0.1to 0.12 howed small decreasing range, especially of alloy with the addition of compound RE. Results were also indicated that SME was improved by increasing quenching temperature (>1000℃): The amount of thermal induced martensite increased and the relative shape recovery ratio could be increased to more than 40after 3-4 times thermal training. The relative shape recovery ratio decreased evidently depending on rising of pre-strain. Furthermore, because speed of martensite transition was extremely great under higher tempering temperature (more than 450℃), ε→γ transition completed in 10s meanwhile the relative shave recovery ratio of the allou increased rapidly.
关键词:
Fe-Mn-Si-Ni-C-ER shape memory alloy
,
null
,
null
N.C.Si
金属学报(英文版)
The effects of heat treatment on the Cu-Zn-Al shape memory alloys with mixed REwere researched with the help of X-ray diffraction and transmission electron micro-scope (TEM).The results show that the shape memory alloys with martensite can beproduced by adding mixed RE and heat treatment processes holding at 820C -880Cfor 15min,quenching into oil,aging at 150C for 15min,and then holding in waterat 50C for 10min.The alloys have the lowest transformation thermal hysteresis.Among the four experimental heat treatment processes the gradationally quenchingmakes the alloy have the highest transformation temperature and quenching into oilor water at room temperature makes the alloy have the largest thermal hysteresis.Mi-crostructure examination shows that aging at 2000C could destroy the substructuresin lathy martensites in the alloy and form a lot of dislocations,and aging at 250℃could cause the bainite transformation in the alloy.
关键词:
Cu-Zn-Al (RE)
,
null
,
null
,
null
焦桓
,
周万城
,
罗发
复合材料学报
doi:10.3321/j.issn:1000-3851.2003.04.008
研究了Si/C/N纳米晶须的制备、组成和微波介电性能.利用CVD法制备了化学组成一定的纳米Si/C/N晶须,XRD研究发现晶须的物相主要为β-SiC.热重分析表明该晶须在700 ℃以上开始氧化,具有较好的抗氧化性.测定了Si/C/N晶须的复介电常数与作用频率的关系,并计算了介电损耗角正切.依据介电性能数据,分别设计了单层和双层吸波材料,对所设计材料的吸波性能进行了计算.对Si/C/N纳米晶须的吸波机理进行了初步的探讨.
关键词:
Si/C/N
,
抗氧化性
,
复介电常数
,
吸波材料
,
吸波机理
刘晓魁
,
周万城
,
罗发
,
朱冬梅
稀有金属材料与工程
采用化学气相沉积方法,在1200℃～1600℃温度范围内,于不同的NH3流量条件下,合成了Si/C/N纳米粉体,研究了粉体的制备工艺、成分、相组成与其微波介电性能之间的关系.结果表明:NH3流量增加,粉体中N含量升高,随着合成温度的提高,粉体的晶化程度增强,主要为β-SiC相.在SiC晶格中固溶有N原子,且N原子的固溶量随合成温度升高而减少.Si/C/N纳米粉体中SiC微晶含量,以及SiC微晶中固溶的N原子浓度对粉体的ε',ε(")和损耗因子tgδ(ε"/ε')起着重要作用.N原子固溶所导致的极化驰豫损耗和漏导损耗是Si/C/N纳米粉体具有吸波性能的主要机理.
关键词:
化学气相沉积
,
Si/C/N纳米粉体
,
微波介电性能
,
吸波机理
Ceramics International
alpha-Si3N4 whiskers have been prepared from the laser-synthesized nanometric amorphous Si-N-C powders at 1873 K under 1 atm N-2. The as-formed whiskers were characterized by TEM, STEM, FTIR and XRD techniques and the process conditions were studied. The whiskers exhibit four types of morphologies: the long, thick, straight, the prismatic, the ribbon-like, and knuckled whiskers. The gas phase reaction among N-2, SiO, and CO gases leads to the formation of Si3N4, nucleated on the pre-crystallized alpha-Si3N4 grains, which ensures an in situ formation, and grows rapidly by a VS mechanism along specific crystal planes such as {1101}. Thermochemical analysis indicates that the higher Si3N4 whisker formation temperature of 1873 K for the gas phase reaction results from the lower P-CO/P-SiO ratio in the Si-N-C system.
关键词:
chemical-vapor-deposition;silicon-nitride;si3n4
卢国锋
硅酸盐通报
本研究采用CVI方法制备出了以Si-C-N陶瓷为基体以热解碳为界面的碳纤维增强陶瓷基复合材料(C/PyC/Si-C-N).用热膨胀仪和激光导热仪分别测试了C/PyC/Si-C-N的热膨胀性能和热扩散性能.研究结果表明:在25～1200℃范围内,C/PyC/Si-C-N复合材料的平均热膨胀系数为0.638×106 K-1;而热扩散率则随温度的升高而减小,并与温度呈一种指数关系,常温下的热扩散率约为0.00925 cm2·s-1.
关键词:
复合材料
,
热膨胀
,
热扩散
,
Si-C-N陶瓷
卢国锋
,
乔生儒
,
焦更生
,
徐浩龙
材料工程
doi:10.3969/j.issn.1001-4381.2011.09.016
本研究制备出了以莫来石为界面层的炭纤维增强Si-C-N陶瓷基复合材料(C/Mullite/Si-C-N).使用三点弯曲法研究了复合材料在室温、1300℃和1600℃时的弯曲断裂行为,利用扫描电镜(SEM)和透射电镜(TEM)观察了复合材料的组织和弯曲断口形貌.结果表明:在室温和1300℃时,C/Mullite/Si-C-N复合材料的断口呈现出明显的脆性断裂特征；而在1600℃时,则呈现出韧性断裂特征.1300℃时的弯曲强度高于室温强度,模量则与室温下的基本相等.1600℃时,复合材料的弯曲强度和模量都明显下降.与具有热解炭界面层的C/Si-C-N复合材料相比,采用莫来石界面后,C/Si-C-N复合材料的强度明显下降.
关键词:
弯曲强度
,
C/Si-C-N复合材料
,
莫来石
,
界面层
Ceramics International
The dispersion behavior of laser synthesized Si-C-N nanopowders in 15 pure organic liquids has been studied through particle size analysis and sedimentation test. The Van der Waals potential energy of interaction between the particles and organic liquid molecules, i.e. V-A, is estimated. The results are correlated with the surface composition of powders and the chemical and physical characteristics of the organic liquids. Poor dispersions are found in nonpolar hydrocarbons, whereas in polar organic liquids, the dispersity and stability depend on the functional group, dielectric constant and carbochain length of the organic liquids. After some of the organic groups on the powder surfaces are eliminated by heat-treatment, the dispersity is decreased. The V-A Of the dispersions can be adequately used to predicate the stability of the nonpolar hydrocarbon dispersions. However, in polar organic liquids, the contribution coming from the electric double layers and solvation layers should also be considered. (C) 2001 Elsevier Science Ltd and Techna S.r.l. All rights reserved.
关键词:
suspensions;surfaces;Si-C-N;ceramic materials;silicon;stability;powders;forces
张颖
,
张军战
,
刘民生
硅酸盐通报
对Si3N4-C和SiO2-C-N2系统中的主要化学反应以及SiC晶须在两种系统中合成的热力学条件进行了分析,进而采用碳黑为碳源、Si3N4与SiO2微粉为硅源、氧化硼为催化剂,分别在氩气与氮气气氛下,于1600℃合成SiC晶须.采用扫描电子显微镜,透射电子显微镜等分析手段分析了晶须的生成量和形貌结构特征.结果表明:通过SiO2-C-N2系统可以一步合成SiC晶须,其与Si3N4-C系统合成的均为β-SiC;但在晶须的生成量和质量上,Si3N4-C系统合成的SiC晶须较好.
关键词:
SiC晶须
,
热力学
,
合成系统
,
形貌结构特征
Journal of Materials Science
The morphology and growth characteristics of alpha-Si3N4 whiskers grown by pyrolysis of amorphous Si-N-C powders were investigated mainly by TEM. It was found that the whiskers exhibited various morphologies including ribbon-, rod-, prism- and nodule-like whiskers. Three growth directions were found: {<1(1)over bar 00>}*, {1010}*, and {0001}* which are dense planes in the hexahedral structure of alpha-Si3N4. No bobbles existed on the whisker tips, but there was a leading growth along the whisker long axial directions and small Si3N4 grains bonded on the whisker tips, which indicated that the whiskers nucleated on small alpha-Si3N4 grains and grew by a vapour-solid condensation mechanism.
关键词:
nitride
