放电等离子制备Ti3AlC2/TiB2复合材料及性能

采用放电等离子烧结(spark plasma sintering,SPS)工艺制备了Ti3AlC2/TiB2复合材料,并研究了复合材料的性能.研究表明:在1 250℃,30MPa烧结8min,可以获得相对密度达98%以上的致密Ti3AlC2/TiB2块体材料;在Ti3AlC2中添加TiB2能大幅度提高材料性能,当TiB2含量为30%(体积分数,下同)时,Ti3AlC2/30%TiB2复合材料的Vickers硬度达到10.39GPa,电导率为3.7×106 S/m;当TiB2含量为10%时,抗弯强度为696MPa,断裂韧性为6.6MPa·m1/2.用电子显微镜对复合材料的显微结构分析表明:Ti3AlC2/TiB2复合材料的晶粒为层状结构.     

热压法制备Al2O3/TiB2/AlN/TiN复合陶瓷

将金属Al,Al3Ti和TiB2以AlTiB中间合金的形式引入Al2O3基体材料中,利用热压法制备Al2O3/TiB2/AlN/TiN复合陶瓷.探讨了复合陶瓷致密化程度与AlTiB体积含量之间的关系.复合陶瓷在烧结过程中属过渡液相烧结.烧结过程中Al,Ti和N2(保护气氛)通过化学反应生成新相AIN和TiN.对热压烧结后材料的硬度、断裂韧性和抗弯强度进行了测试和分析.分析了复合陶瓷的力学性能随AlTiB体积含量变化的规律.比较了复合陶瓷1500℃和1600℃的相对密度及力学性能.探讨了复合陶瓷断面断裂方式的变化对其力学性能的影响,并分析了AlTiB中间合金的细化特性.     

放电等离子烧结SiC/BN复相陶瓷的制备及力学性能

以高纯h-BN和SiC纳米粉体为原料、B_2O_3为烧结助剂,利用放电等离子烧结技术(SPS)快速烧结制备了h-BN–25%SiC复相陶瓷。用X射线衍射和扫描电子显微镜对试样的物相组成和显微结构进行分析,研究了h-BN–SiC复相陶瓷的SPS低温烧结行为及烧结温度对烧结试样的致密度、微观结构及力学性能的影响。结果表明:采用SPS烧结技术,在较低温度下即可获得致密度较高的烧结样品,烧结温度的升高,促进了h-BN晶粒的方向性排列,提高了烧结样品的相对密度。随着烧结温度的提高,晶粒尺寸增大,抗弯强度、断裂韧性和弹性模量增大,并具有相同的变化趋势。样品晶粒细小均匀,不同烧结温度样品的断裂方式相同,主要为沿晶断裂,细小SiC颗粒的钉扎效应、晶粒拔出和裂纹偏转提高了复相陶瓷的断裂强度和断裂韧性。在1 600℃烧结所得试样的综合性能较好,其抗弯强度、断裂韧性和弹性模量分别为289.2 MPa、3.45 MPa·m1/2和150.9 GPa。     

烧结温度对BN-ZrB_2-ZrO_2复相陶瓷结构与性能的影响

以h-BN为基体材料,ZrO2、AlN、B2O3和Si等为改性剂,采用反应热压烧结工艺制备BN-ZrB2-ZrO2复相陶瓷,研究了烧结温度对BN基复相陶瓷物相组成、致密化、微观结构及力学性能的影响。结果表明:提高烧结温度可促进ZrB2相的形成,烧结后的复合陶瓷中出现SiAlON相;随烧结温度升高,样品相对密度、抗弯强度和断裂韧性都呈现先升高后降低趋势,烧结温度为1 900℃时材料的相对密度、抗弯强度和断裂韧性最高,分别为95.2%、226.0MPa和3.4MPa·m1/2。ZrB2相的存在显著提高了BN基复相陶瓷的力学性能。与热压烧结纯BN陶瓷相比,BN-ZrB2-ZrO2复相陶瓷的抗弯强度提高了183%,且该复相陶瓷主要以沿晶断裂为主,高温下烧结的样品中出现晶粒拔出现象,并伴随有少量穿晶断裂。     

粉体合成工艺对TiB_2–TiC复相陶瓷微观组织及力学性能的影响

分别以直接法和间接法碳硼热还原工艺合成的TiB_2–TiC复合粉体为原料,采用热压烧结工艺制备了共晶成分的TiB_2–44%TiC(摩尔分数)复相陶瓷,研究了粉体合成工艺和烧结温度对TiB_2–TiC复相陶瓷显微组织和力学性能的影响。结果表明:以直接法合成粉末为原料烧结的TiB_2–TiC复相陶瓷中,TiB_2晶粒多呈棒状、组织细小均匀;而以间接法合成粉末为原料制备的复相陶瓷中TiB_2晶粒多呈等轴状。随着烧结温度的升高,复相陶瓷致密度提高,晶粒长大,但力学性能变化不明显。以直接法合成复合粉末为原料,在烧结温度为2 000℃、压力为30 MPa、保温时间为1 h工艺条件下制备的TiB_2–TiC复相陶瓷综合性能最佳,其致密度、弹性模量、Vickers硬度、抗弯强度和断裂韧性分别为99.9%、537 GPa、19.0 GPa、598 MPa、5.3 MPa·m~(1/2)(压痕法)和11.6 MPa·m1/2(单边切口梁法)。TiB_2–TiC复相陶瓷主要的增韧机制为裂纹偏转和分叉。     

添加TiB_2对SiC基复相陶瓷显微结构和力学性能的影响

以钇铝石榴石(YAG)为助烧剂,利用等离子放电烧结(SPS)制备SiC–TiB_2复相陶瓷。采用X射线衍射、扫描和透射电子显微镜、能量色散X射线能谱对材料物相及微观结构进行了表征。研究了SPS烧结温度及TiB_2的加入对材料微观结构尤其是晶界相形态和力学性能的影响。结果表明:虽然TiB_2的加入对材料致密化起到了一定的阻碍作用,但是促使晶界相从晶态向非晶态转变,提高了晶粒间结合强度,材料的力学性能得到提升。烧结温度为1 750℃制备的SiC–TiB_2陶瓷抗弯强度最高,为753 MPa,烧结温度为1 700℃制备的SiC–TiB_2陶瓷断裂韧性最高,为8.84 MPa·m~(1/2)。     

烧结温度对气压烧结氮化硅铁显微结构及性能的影响

以微米级氮化硅铁为原料、Al_2O_3–Y_2O_3为烧结助剂,采用气压烧结制备氮化硅铁复相陶瓷。通过X射线衍射和扫描电子显微镜对试样的物相组成和显微结构进行了表征,研究了烧结温度对氮化硅铁复相陶瓷成分、显微结构和力学性能的影响。结果表明:烧结温度对于氮化硅铁陶瓷的显微结构和力学性能具有显著影响。随着烧结温度的升高,样品致密度、抗弯强度、断裂韧性先增大后降低,在1 770℃时均达到最大值,密度、抗弯强度和断裂韧性分别达到3.31 g/cm~3、435 MPa和6.97 MPa?m~(1/2)。在1 770℃以下时,陶瓷样品中主晶相为长柱状的β-Si3N4,晶粒彼此间结合紧密,陶瓷气孔率较低。温度继续升高,含铁相和氮化硅发生反应,气孔率增大,抗弯强度和断裂韧性开始下降。如果进一步提高硅铁的氮化率,采用游离硅低、铁含量低及纯度较高的氮化硅铁粉末制备氮化硅铁陶瓷,材料的性能有望得到进一步的提高。     

(SiC,TiB2)/B4C复合材料的微观结构及性能

以B4C与Si3N4和少量SiC,TiC为原料,Al2O3和Y2O3为烧结助剂,烧结温度为1 800～1 880℃,压力为30 MPa的热压条件下制备(SiC,TiB2)/B4C复合材料.用透射电子显微镜、扫描电子显微镜和能谱分析进行显微结构分析.结果表明:在烧结过程中反应生成了SiC,TiB2和少量的BN.复合材料的主晶相之间有长棒状架构弥散相和束状弥散相,在部分B4C晶粒内部出现了内晶结构.结合对复合材料性能的分析表明:新形成相、均匀细晶和棒状结构对提高材料的性能具有重要作用.通过对材料断口形貌和裂纹扩展模式分析认为,复合材料的断裂机制主要为裂纹偏转.     

添加剂B_2O_3对SiC/h-BN复相陶瓷低温烧结行为及性能的影响

以乱层结构h-BN(t-BN)和SiC纳米粉体为原料,B_2O_3为烧结助剂,利用放电等离子烧结技术(SPS)制备出SiC/h-BN复相陶瓷。采用X射线衍射和扫描电子显微镜对试样的物相组成和显微结构进行分析,研究烧结助剂含量对SiC/h-BN复相陶瓷的低温烧结行为、致密化、微观结构及力学性能的影响。结果表明:利用SPS低温烧结方法,添加少量B_2O_3添加剂,可有效地提高复相陶瓷的致密度和力学性能。与无添加剂烧结样品相比,烧结助剂的添加降低了样品烧结收缩起始温度,促进样品中片状h-BN晶粒的移动和重排,提高了颗粒间的结合强度。随着烧结助剂添加量的增加,复相陶瓷致密度显著增加,强度和韧性均呈现先增加后降低的趋势,在B_2O_3添加量为5%时,复相陶瓷相对密度和各项力学性能较高,其相对密度、抗弯强度、断裂韧性和弹性模量分别为96.92%、274.7MPa、2.91MPa·m1/2和127.2GPa,但添加过多B_2O_3,则不利于提高复相陶瓷的力学性能。     

高能球磨和热压烧结制备SiC/Ti_3SiC_2复相陶瓷及其性能

以Ti,Si和C粉为主要原料,利用高能球磨及热压烧结制备了SiC/Ti3SiC2复相陶瓷。研究了工艺条件尤其是烧结温度和压力对合成产物相组成、微观结构及性能的影响,并结合X射线衍射、扫描电镜等检测结果探讨了Ti-Si-C体系反应合成机理。结果表明:通过高能球磨18h,在25MP和1300oC热压,可得到均匀、致密的SiC/Ti3SiC2复相陶瓷材料。Si含量对SiC/Ti3SiC2材料的相组成及性能有较大影响。起始原料中的Ti,Si,C和Al的质量比为3:1.2:2:0.2时,材料性能提高明显,其弯曲强度、断裂韧性、密度和相对密度分别为526.65MPa,8.67MPa·m1/2,4.058g/cm3,89.78%。显微结构的观察表明,SiC/Ti3SiC2复合材料的断裂具有沿晶和穿晶混合断裂特征。SiC颗粒增韧抑制了微裂纹在Ti3SiC基体中的扩展。     

Effect of sintering temperature on electrical properties of SiC/ZrB2 ceramics

SiC/20?wt% ZrB₂ composite ceramics were fabricated via pressureless solid phase sintering in argon atmosphere at different temperature. The effect of sintering temperature on microstructure, electrical properties and mechanical properties of SiC/ZrB₂ ceramics was investigated. Electrical resistivity exhibits twice significant decreases with increasing sintering temperature. The first decrease from 1900?°C to 2000?°C is attributed to the obvious decrease of continuous pore channels in as-sintered materials. The second decrease from 2100?°C to 2200?°C results from the improvement of carbon crystallization and the disappearance of amorphous layers enveloping ZrB₂ grains. Additionally, the increase of sintered density with increasing temperature caused greatly advance of flexural strength, elastic modulus and Vickers hardness. But excessive temperature is detrimental to flexural strength because of SiC grain growth.     

碳化硼材料的制备技术

本文综述了国内外碳化硼粉末和碳化硼陶瓷制备技术的研究现状与进展情况,重点介绍了碳管炉、电弧炉碳热还原法、自蔓延高温合成法、激光诱导化学气相沉积法、溶胶凝胶碳热还原法合成碳化硼粉末以及热压、热等静压、无压烧结、放电等离子烧结和反应烧结制备碳化硼陶瓷的研究进展。     

铌酸锶钡/钛酸锶钡复相陶瓷形成过程研究

应用粉末-溶胶工艺合成出铌酸锶钡/钛酸锶钡复相陶瓷(SBN/SBT)。采用X射线衍射技术研究了不同预烧温度的原始粉料、不同烧结温度和不同保温时间得到的铌酸锶钡/钛酸锶钡复相陶瓷。研究表明:钨青铜相和钙钛矿相共存于体系之中。复相陶瓷形成过程中形成了TiO2、BaNb2O6(BN)、SrNb2O6(SN)等中间相,增加烧结温度至1250℃,形成了铌酸锶钡/钛酸锶钡复相陶瓷。     

纳米SiC对Al2O3/TiC基多相陶瓷材料显微结构的影响

从烧结温度、基体晶粒大小、断裂方式、SiC在基体中的分布等几方面研究了纳米SiC颗粒的加入对Al2O3/TiC复相基体显微结构的影响.实验表明,纳米SiC颗粒的加入提高了烧结温度,抑制了基体晶粒的异常长大,明显细化了晶粒.试样的断裂方式从以沿晶断裂为主转变为以穿晶断裂为主.纳米SiC在基体中分布均匀,部分位于晶粒内,另一部分位于晶界上.这种显微结构有利于材料力学性能的提高.     

Development of matrix microstructure in polycrystalline cubic boron nitride ceramics

The development of matrix microstructure in polycrystalline cubic boron nitride cutting tool materials has been investigated by X-ray diffraction and scanning and transmission electron microscopy combined with energy dispersive X-ray spectrometry. The materials had a matrix based on Ti(C,O,N) and Al and were fabricated from powder mixtures milled with either WC-Co cemented carbide or (Ti,W)(C,N)-Co cermet milling media. The introduction of WC-Co debris resulted in the formation of an Al- and W-rich liquid phase during high pressure high temperature sintering. Crystalline intergranular phases rich in W partitioned from this liquid. Debris from the cermet milling media resulted in the formation of intergranular Co₂B; the W was retained in the (Ti,W)(C,N) structure during sintering. Al-rich reaction zones on cBN grain surfaces developed locally during high pressure high temperature sintering.     

Y_2O_3添加剂对SiC复相多孔陶瓷烧结性能和力学性能的影响

利用添加造孔剂法制备SiC复相多孔陶瓷。研究了Y2O3添加剂对SiC复相多孔陶瓷的烧结温度及烧结体力学性能的影响机理。结果表明:Y2O3的加入大大降低了SiC复相多孔陶瓷烧结温度,样品的力学性能有所提高,抗弯强度提高18.46%,稀土氧化物占总质量3%时能提高SiC复相多孔陶瓷的抗氧化性,氧化速率降低了66.7%。YAG相在SiC晶界均匀分布,细晶,裂纹偏转及晶界桥联是SiC复相多孔陶瓷的增韧的机理。     

Revealing correlation of core‒rim structures,defects and stacking-faults in SiC ceramics by integrated scanning electron microscopy

Dopant distribution is key to understand sintering behavior and microstructure?property relationship of silicon carbide (SiC) ceramics. Using high-angle secondary-electron (SE) imaging in scanning electron microscope combining elemental and cathodoluminescence (CL) analysis, core?rim structures were found as common microstructural features in SiC ceramics sintered with rare-earth oxides. Characteristic emission by donor-accepter-pairs (DAP) could reveal co-solution of Al?N in α- and β-SiC phases in hot-pressed and gas-pressure sintered ceramics, with or without AlN co-dopant. Stacking-faults (SFs) were found in β-SiC grains to emit characteristic photons by local twin-structures, which confine the luminous transition by DAP into a quantum effect and suppress fully the luminescence when SF density reaches a limit by sintering with two rare-earth oxides. Systematic correlation between the development of microstructures, solution and defect luminescence, and phase transformation can lead to hierarchical microstructure?property relationship to study synergetic mechanical, thermal and opto-electrical performance of SiC ceramics as well as electronic materials.     

Fabrication and thermoelectric properties of SrTiO3–TiO2 composite ceramics

The paper presents the results of preparing biphase SrTiO₃–TiO₂ ceramics as a promising system for n-type thermoelectrics using the features of a two-dimensional electron gas. Ceramics was obtained by reactive spark plasma sintering of SrCO₃ and TiO₂. The dynamics of phase transformations are shown; it is clarified that phase transformations are not the driving force of sintering. The mutual stabilization of the SrTiO₃ and TiO₂ phases is shown. Unique data on the assessment of the temperature gradient in the system have been obtained. A comparison of the thermoelectric characteristics of biphasic ceramics and its constituent phases allows concluding that the role of the two-dimensional electron gas is reduced to modulating the properties of bulk phases. Clear signs of size quantization were detected by the X-ray luminescence method, which is expressed in the blueshift of the luminescence spectrum by 22.3 ± 0.8 meV.     

无压烧结制备表面微孔碳化硅陶瓷

以碳化硅（SiC）微粉为骨料,Al2O3-Y2O3为烧结助剂,氯化钙（CaCl2）作为造孔剂,采用无压液相烧结制备了表面微孔SiC陶瓷,分析了不同CaCl2含量对SiC陶瓷的烧结性能、显微结构和摩擦性能的影响。结果表明：加CaCl2会降低SiC陶瓷的体积密度、硬度和抗弯强度;可以有效地细化SiC陶瓷晶粒;能在SiC陶瓷...     

Al2O3-SiC复相陶瓷材料制备方法的研究现状

简要论述了Al2O3-SiC复相陶瓷材料的常用制备方法,如无压烧结法、热压烧结法、气压烧结法和溶胶-凝胶法等,重点介绍了碳热还原法。对以不同原料制备Al2O3-SiC复相陶瓷材料的碳热还原法进行了比较,指出了这方面研究的不足之处和下一步研究的方向。