包覆法制备Gp/SiC复合材料的显微结构和性能

以不同粒径的石墨颗粒和SiC粉体为原料,采用SiC粉体包覆石墨颗粒的方法,于2000℃热压制备了石墨/碳化硅（Gp/SiC）复合材料.利用扫描电子显微镜（SEM,EDS）分析了材料的金相和断口显微结构.研究表明,石墨粒径较小且质量分数较少的复合材料比石墨粒径较大且质量分数较多的复合材料在热压工艺中更致密.石墨颗粒呈岛状紧密地镶嵌在SiC基体中,石墨与SiC界面处C和Si的扩散不明显.复合材料的相对密度、抗折强度,断裂韧性和硬度随石墨粒径和质量分数的减少而增加.断口形貌表明SiC陶瓷基体为脆性,石墨为韧性断裂.当石墨粒径为125μm、SiC与石墨的质量比为3.5时,复合材料的综合性能最佳,开口气孔率为0.3%,相对密度为97.9%,抗折强度为75±15 MPa,断裂韧性为5.4±0.5 MPa.m1/2,硬度为26.8±3GPa.     

Ti3SiC2/TiB2复合材料的制备及其组织和力学性能

以2TiC／Ti／Si／0．2Al／TiB2粉为原料，采用热压烧结工艺成功制备了Ti3SiC2／TiB2复合材料。结果表明：不同TiB2含量的试样中主晶相为Ti3siC2与TiB2两相，没有发现其它杂质相；当复合材料中TiB2的体积分数为10％时，其硬度、抗压强度、弯曲强度、断裂韧性都有显著的提高。经热处理后，Ti3SiC2／10％TiB2复合材料的弯曲强度由367．5MPa     

B4C／TiO2／Al复合材料制备及其性能

采用热压法制备了B4C／TiO2／Al复合陶瓷材料，试验结果表明，TiO2和Al的加入，使得B4C／TiO2／Al复合材料的硬度、抗弯强度和断裂韧性比纯B4C陶瓷材料有较大程度的提高；而且，添加相促进了复合材料的烧结．利用热力学和X射线衍射分析研究烧结过程中的化学反应，分析结果表明，复合材料中没有发现TiO2，Al，Al2O3;同时在复合材料中出现了TiB2，因为在热压过程中TiO2-B4C反应生成TiB2．分析了B4C／TiO2／Al复合陶瓷材料的微观结构和增韧机理．     

无压烧结SiC/TiB2复合材料组织与性能的研究

以TiB₂为基体、SiC为主要添加相、B₄C和纳米炭黑为烧结助剂，采用无压烧结方法制备SiC/TiB₂复合材料，研究SiC添加量对SiC/TiB₂复合材料的显微组织、力学性能及体积电阻率的影响。结果表明：随着SiC含量的增加，复合材料的晶粒尺寸逐渐减小，开口气孔率逐渐降低，抗折强度、断裂韧性及维氏硬度均呈现上升趋势；当SiC的质量分数为20%时，复合材料的力学性能最佳，此时其抗折强度、断裂韧性和维氏硬度分别为189.5 MPa、4.19 MPa·m^1/2和15.8 GPa;随着SiC含量的增加，复合材料的体积电阻率增大，导电性能有所降低。     

TiB_2/SiC陶瓷复合材料制备工艺的研究

以TiO2、B4C和C为原料,基于原位合成法在SiC基体中生成TiB2颗粒,并采用无压烧结法制备出TiB2/SiC复合陶瓷.通过对复合材料制备工艺的研究,发现：高于1 300℃的预烧结能形成TiB2/SiC复合陶瓷坯体.C含量、烧结温度和保温时间对复合材料的相对密度均有影响.当C含量（质量分数）为4%时、在1 400℃×60 min＋2000℃×30 min的烧结工艺下能够制备出致密的TiB2/SiC陶瓷复合材料.微米级TiO2粉比纳米级TiO2粉更有利于形成较致密的烧结复合材料.随着生成TiB2体积分数的增加（5%～20%）,复合材料中TiB2颗粒逐渐粗化,间距逐渐变小.对复合材料的烧结机理还进行了分析.     

B4C/TiO2/Al复合材料制备及其性能

采用热压法制备了B4C/TiO2/Al复合陶瓷材料，试验结果表明，TiO2和Al的加入，使得B4C/TiO2/Al复合材料的硬度、抗弯强度和断裂韧性比纯B4C陶瓷材料有较大程度的提高；而且，添加相促进了复合材料的烧结.利用热力学和X射线衍射分析研究烧结过程中的化学反应，分析结果表明，复合材料中没有发现TiO2，Al，Al2O3；同时在复合材料中出现了TiB2，因为在热压过程中TiO2与B4C反应生成TiB2.分析了B4C/TiO2/Al复合陶瓷材料的微观结构和增韧机理.     

掺加SiC晶须对B4C—Al2O3复合材料性能的影响

B4C-20vol%Al2O3和B4C-30vol%Al2O3两种材料分别掺加了15vol%(体积比)的SiC晶须(SiCw)在1850℃、35MPa下热压烧结40min.结果表明SiCw的掺入,使复合材料的力学性能下降,特别是B4C-30vol%Al2O3材料的性能下降更为明显,弯曲强度和断裂韧性由原先的389.5MPa和5.76MPa@m1/2,分别下降到293.4MPa和4.11MPa@m1/2.通过分析找出了SiCw对复合材料性能产生影响的原因.     

碳化硅-二硼化钛复合陶瓷性能研究

采用无压烧结,利用小分子的B、C作为烧结助剂在2180℃获得了相对密度为96％的SiC—TiB2复合材料,XRD分析显示在烧结过程中无新相产生,从烧结体的显微形貌可以看出,在烧结过程中有包晶现象,SiC颗粒有明显长大趋势．大的晶粒存在使烧结体的力学性能降低,主要表现为抗弯强度和断裂韧性不高,分别只有158．6MPa和2．85MPa·m^1/2．     

掺加SiC晶须对B_4C-Al_2O_3复合材料性能的影响

B4C－ 20vol％ Al2O3和 B4C－ 30vol％ Al2O3两种材料分别掺加了 15vol％ (体积比 )的 SiC晶须 (SiCw)在 1850℃、 35MPa下热压烧结 40min。结果表明： SiCw的掺入,使复合材料的力学性能下降,特别是 B4C－ 30vol％ Al2O3材料的性能下降更为明显,弯曲强度和断裂韧性由原先的 389.5MPa和 5.76MPa· m1/2,分别下降到 293.4MPa和 4.11MPa· m1/2。通过分析找出了 SiCw对复合材料性能产生影响的原因。     

SHS工艺制备TiC-TiB2/Cu-Ni复合材料的性能

以Ti和B4C粉末为主要原料，以金属Cu,Ni为粘结剂，利用SHS／PHIP工艺制备了TiC-TiB2／Cu-Ni系复合材料，通过实验研究了该系列复合材料的微观结构特征和力学性能．结果表明，TiC-TiB2／Cu-Ni系复合材料中只有TiC、TiB2、及Cu(Ni)相存在；随着金属含量的增加，燃烧温度下降，颗粒尺寸变小；由于Ni的加入改善了陶瓷／金属的浸润性，双掺Cu-Ni的TiC-TiB2陶瓷基复合材料力学性能最高，其相对密度为98．5％、断裂韧性最高值达到11．6MPa．m^1/2．     

烧结温度对BN陶瓷材料强度的影响

采用热压烧结(HP)法制备纯BN陶瓷和B2O3-BN陶瓷复合材料．利用三点弯曲方法测定了这两种材料的抗弯强度、弹性模量等力学性能，通过扫描电镜对两种材料的断口进行了分析。结果表明：纯BN陶瓷烧结温度达到1800℃时相对质量密度和强度较低；添加B2O3烧结温度超过900℃时可以形成液相，改善了BN的烧结性能，提高了B2O3-BN复合陶瓷的相对质量密度，从而提高了材料的强度。     

Synthesis of Ti3SiC2/TiB2 Composite by In-situ Hot Pressing (HP) Method

Ti3SiC2/TiB2 composite was successfully obtained by hot pressing Ti/TiC/Si/B4C power mixtures.Volume fraction of TiB2 in Ti3SiC2/TiB2 composite can not exceed 10%.Incorporation of excessive TiB2 will affect the reactions process.TiC and Ti5Si3 were two important intermediate phases during the whole reactions.The microstructure characteristics of the Ti3SiC2/TiB2 composites were analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM).The experimental results show that the grains of Ti3SiC2/TiB2 composite are structured in a layered form,and the formation of TiB2 particles as reinforcements with elongated or equiaxed shape distributes in Ti3SiC2 matrix.     

莫来石基复合材料的显微结构与增韧特性(Ⅰ)——SiCw/莫来石体系

采用溶胶-凝胶工艺合成的高纯莫来石粉及Tokai碳化硅晶须,以热压方法制备了SiCw/莫来石系复合材料。高纯莫来石陶瓷呈现较高的强度和相当高的断裂韧性,添加SiC晶须后其强度和韧性进一步提高。根据显微结构分析认为,桥联和造成裂纹偏转是晶须的主要增韧机制。清除SiC晶须表层的SiO_2,利于其增韧效应的发挥。     

SiC WHISKER-TOUGHENED ALUMINIUM NITRIDE CERAMICS

Aluminium nitride ceramics containing 15-30 w/o of SiC whiskers can be sintered tofull density(by hot pressing at 1800℃)using2-3 w/o of Y_2O_3,additions.The whiskersincrease the toughness and strength of thecomposite,K_(10) increasing from 2.8 to about5.0 and flexural strength increasing by 30-50%.However,the whiskers must be welldispersed and if the dispersion is notsatisfactory,toughness may increase but thestrength decreases.The hot-pressingtemperature can be reduced by up to 100℃ ifY(NO_3)_3 .5H_20 is used as the sinteringadditive instead of Y_2O_3,but some oxidation ofthe AIN occurs during heating.Isopropan-2-01 is a better dispersing agent thancyclohexane,but again some oxidation of theAIN does occur.The best sample prepared during this work contained 20 w/o of SiC whiskers and 2 w/oY_2O_3 added as Y(NO_3)_3. 5H_2O and mixed inisopropanol.This exhibited a mean strength of453MPa(maximum 522MPa,measured bydisc flexure)and a fracture toughness of5.5MPam~(1/2).     

Preparation and properties of multi-wall carbon nanotube/SiC composites by aqueous tape casting

MWCNTS/SiC composites were fabricated by aqueous tape casting. High solid content (50 vol%) SiC slurries with sintering additives and multi-wall carbon nanotubes (MWCNTs) as reinforcements were prepared using Tetramethylammonium hydroxide as the dispersant. The stability of MWCNTs/SiC slur-ries was studied and characterized in terms of zeta potential and rheology measurements. The relative density of the composite was about 98% after hot-pressing at 1850℃ (at 25 MPa in Ar for 30 min). The hardness of the composites decreased with the increase in MWCNTs content. The flexural strength and the fracture toughness were 742.17 MPa and 4.63 MPa·m1/2, respectively when the MWCNTs content was 0.25 wt%. Further increase in MWCNTs content to 0.50 wt% did not lead to the increase in mechanical properties. Most of MWCNTs were found to be located at SiC grain boundaries and the pull out of the MWCNTs was observed.     

Preparation of BN／SiO2 ceramics by PIP method

The precursor infiltration and pyrolysis(PIP) method for preparation of BN/SiO2 composites was used to improve mechanical properties, dielectric properties and feasibility of high temperature dielectric parts with large dimensions and complex shapes. In the processing procedure, the porous BN ceramic matrix was first successfully prepared by compacting the mixed powders of B and BN and then sintering them at a certain temperature under normal pressure of N2. The polycarbosilane(PCS) solution was vacuum infiltrated into porous BN ceramics at the room temperature and then at 800℃ in the air to depolimerize out amorphous SiO2, and sintered further at 1 300℃ in N2 to get BN/SiO2 composites. The microstructure of materials was studied by means of X-ray diffraction and electron probe micro analysis. The thermo-decomposition mechanism of PCS was investigated by a TG-DTA and infrared (IR) spectrum analysis. The flexural strengths were measured by the three-point bending method. The dielectric constant and the loss tangent were measured by the wave-guide method. The results show BN/SiO2 composites were fabricated. The obtained composites posses a flexural strength of 61.96 - 93.31 MPa, the dielectric constant in the range of 3.50 - 3.78 and the order of magnitude of the loss tangent at 10^-3 , which are good for the high tempera turedielectric parts with large size and complex shapes.     

β－SiAlON－cBN陶瓷复合材料的制备与性能

采用放电等离子烧结（SPS）在1500℃下制备不同立方氮化硼（cubic Boron Nitride,即cBN）含量的β－SiAlON－cBN陶瓷复合材料,研究cBN含量对陶瓷复合材料的物相组成、显微组织和性能的影响．XRD分析表明：在添加复合烧结助剂的条件下合成的β－SiAlON－cBN陶瓷复合材料,β－SiAlON的量随着cBN含量的增加而增加．FESEM观察结果表明：cBN颗粒较均匀地分布在β－SiAlON基体中,一些cBN颗粒表面出现可剥离的层片状物质六方氮化硼（hBN）．随着cBN含量的增加,β－SiAlON－cBN陶瓷复合材料的相对密度先下降后略有上升,硬度呈现降低趋势,断裂韧性则先升高后略有降低．β－SiAION－10％cBN（质量分数）的相对密度和硬度分别为96．8％和13GPa,β－SiAlON－30％cBN的断裂韧性可达到KIC=3．2MPa·m^1/2．