自蔓延高温合成氮化硅多孔陶瓷的研究进展

多孔氮化硅陶瓷兼具有高气孔率和陶瓷的优异性能, 在吸声减震、过滤等领域具有非常广泛的应用。然而, 目前常规的制备方法如气压/常压烧结、反应烧结-重烧结以及碳热还原烧结存在烧结时间长、能耗高、设备要求高等不足, 导致多孔Si₃N₄陶瓷的制备成本居高不下。因此, 探索新的快速、低成本的制备方法具有重要意义。近年来, 采用自蔓延高温合成法直接制备多孔氮化硅陶瓷展现出巨大潜力, 其可以利用Si粉氮化的剧烈放热同时完成多孔氮化硅陶瓷的烧结。本文综述了自蔓延反应的引发以及所制备多孔氮化硅陶瓷的微观形貌、力学性能和可靠性。通过组分设计和工艺优化, 可以制备得到氮化完全、晶粒发育良好、力学性能与可靠性优异的多孔氮化硅陶瓷。此外还综述了自蔓延合成多孔Si₃N₄陶瓷晶界相性质与高温力学性能之间的关系, 最后展望了自蔓延高温合成多孔Si₃N₄陶瓷的发展方向。     

Effect of seed particles content on texture formation of Si_3N_4 ceramics by gel-casting in a strong magnetic field

In this paper,the textured Si_3N_4 ceramics were prepared by adding seed particles during gel-casting in the magnetic field of 6 T,followed by pressureless sintering.The effect of pH on the stability and dispersibility of Si_3N_4 slurry and the effect of seed particles content on texture formation of Si_3N_4 ceramics were both studied.Those results showed that the slurry with good stability and dispersibility was obtained when pH was about 11.6.The a or b-axis of Si_3N_4particles or crystals was aligned parallel to the direction of the magnetic field in the magnetic field of 6 T.The degree of texture of Si_3N_4 ceramics further increased during sintering.With the increasing of additional β-Si_3N_4 particles in the magnetic field of 6 T,the degree of texture increased from0.19 without seed particles to 0.76 with 9%(mass fraction)seed particles.The increase of seed particles content promoted the texture formation of Si_3N_4 ceramics.     

Microstructural and piezoelectric properties of low temperature sintering PMN-PZT ceramics with the amount of Li2CO3 addition

PMN-PZT ceramics doped with Li₂CO₃ and Bi₂O₃ as sintering aids were manufactured in order to develop the low temperature sintering ceramics for multilayer piezoelectric transformer, and their micro structural, dielectric and piezoelectric properties were investigated. The sintering aids were proved to lower the sintering temperature of doped PMN-PZT ceramics due to the effect of LiBiO₂ liquid phase. Optimal values for multilayer piezoelectric transformer application, such as electromechanical coupling factor (k_p) of 0.50, mechanical quality factor (Q_m) of 2264, and dielectric constant (K) of 1216, and curie temperature (T_c) of 317 °C were found at 0.1 wt.% Li₂CO₃ added ceramics sintered at 940 °C.     

添加BaTiO3的热压烧结Si3N4陶瓷的力学和介电性能

本研究以Al₂O₃和Nd₂O₃为烧结助剂, 采用热压烧结法制备Si₃N₄陶瓷, 系统研究了添加BaTiO₃对Si₃N₄陶瓷力学和介电性能的影响。研究结果表明, 随着BaTiO₃含量的增加, 相对密度、抗弯强度和维氏硬度都随之降低, 而断裂韧性有所升高; 即使添加5wt%~20wt%的BaTiO₃, Si₃N₄陶瓷的抗弯强度依然可以保持在600 MPa以上。Si₃N₄陶瓷的介电常数可以提高到9.26~11.50, 而介电损耗保持在10^-3量级。在Si₃N₄陶瓷中未检测到BaTiO₃结晶相, 可以认为Si₃N₄陶瓷介电常数的提高主要来源于烧结过程中形成的TiN。这些结果有助于拓展Si₃N₄陶瓷的应用领域。     

稀土氧化物对常压烧结氮化硅陶瓷性能的影响

高导热氮化硅陶瓷是大功率电力电子器件散热的关键候选材料。研究采用稀土氧化物(Re₂O₃)和氧化钛(TiO₂)烧结助剂体系, 通过低温常压烧结方法来制备氮化硅陶瓷, 以有效降低成本, 满足实际应用的需求。系统研究了烧结助剂种类及含量对Si₃N₄陶瓷的致密化行为、热导率、显微结构以及力学性能的影响。研究发现随着稀土离子半径的增大, 材料的致密度和热导率均呈现下降趋势, 添加Sm₂O₃后样品最高密度仅为3.14 g/cm³。但是当Sm₂O₃-TiO₂烧结助剂含量为8wt%时, 样品断裂韧性可达5.76 MPa•m^1/2。当添加Lu₂O₃且烧结助剂含量为12wt%时, 材料的密度可达3.28 g/cm³, 但是大量存在的第二相导致热导率仅为42.3 W/(m∙K)。研究发现该材料具有良好的断裂韧性。经1600℃退火8 h后, Er₂O₃-TiO₂烧结助剂样品的热导率达到51.8 W/(m∙K), 基本满足一些功率电路基板材料的实际应用需求。     

氮气压力对多孔氮化硅陶瓷显微组织和力学性能的影响

以α-Si₃N₄为原料, Y₂O₃为烧结助剂, 在三种不同的氮气压力(0.12、0.32和0.52 MPa)下烧结制备了多孔氮化硅陶瓷。研究了氮气压力对氮化硅的烧结行为、显微组织和力学性能的影响, 分别通过SEM观察显微组织并统计晶粒的长径比, 通过XRD对物相进行分析, 并对烧结试样进行三点弯曲强度测试。随着氮气压力的提高, 多孔陶瓷的线收缩率降低、气孔率提高, 这是由于低熔点的液相中N含量随氮气压力的提升而增加, 导致了液相粘度提高, 抑制陶瓷致密化。随着氮气压力的提高, 组织中的棒状β-Si₃N₄生长良好, 晶粒长径比增大, 其原因是高的液相粘度抑制了β-Si₃N₄形核, 有利于β-Si₃N₄生长。由于β-Si₃N₄棒状晶的作用, 陶瓷弯曲强度随氮气压力的升高得到改善, 但是气孔率的升高降低陶瓷的强度。在0.52 MPa的氮气压力下烧结的多孔陶瓷气孔率达58%, 弯曲强度为140 MPa。     

The effect of Si3N4 on the thermal expansion behavior of MoSi2

The effect of Si₃N₄ particulates on the thermal expansion coefficient (CTE) of MoSi₂ was investigated. It was observed that as the volume percent of Si₃N₄ increases, the CTE of the MoSi₂-Si₃N₄ composites decreases. In the temperature range 1000–1500 °C, typical of that required for glass melting, about 30–35 vol% Si₃N₄ particulates are needed in the MoSi₂-Si₃N₄ composites such that the CTE of the composite matches the CTE of Mo.     

Investigation of the physical and mechanical properties of hot-pressed machinable Si3N4/h-BN composites and FGM

A new design method of machinable ceramic composites was proposed, which applies the graded-structure concept to the design of machinable Si₃N₄ ceramics. Silicon nitride/hexagonal boron nitride (h-BN) ceramic composites and functionally graded materials were fabricated by hot pressing at 1750 °C for 2 h, varying the alignment of the amount of hexagonal BN using powder layering method. The improved machinability of Si₃N₄/h-BN composite can be attributed to addition of layered structure hexagonal BN. Hexagonal BN possesses excellent cleavage planes perpendicular to the c-axis. Ease of machining depends on degree of crystal interlocking; hence volume content of h-BN crystals and their aspect ratio affect machinability. The texture of h-BN and β-Si₃N₄ was observed during hot pressing sintering. Physical and mechanical properties of Si₃N₄/h-BN with different content of h-BN were investigated, such as bulk density, Vickers's hardness, flexural strength, and elastic modulus. All of these properties are important for the design of the machinable Si₃N₄/h-BN FGM (Functionally Graded Materials).     

Thermal stability and crystallization kinetics of sputtered amorphous Si3N4 films

The crystallization of thin silicon nitride (Si₃N₄) films deposited on polycrystalline SiC substrates was investigated by X-ray diffractometry as a function of annealing time. The amorphous Si₃N₄ films were produced by means of reactive r.f. magnetron sputtering. Annealing at temperatures between 1300 and 1700 °C led to the formation of crystalline films composed of -Si₃N₄ and β-Si₃N₄. The fraction of β-Si₃N₄ in the films reaches approximately 40% at temperatures above 1550 °C. Both polymorphic modifications were formed simultaneously during the crystallization process. A transformation of -Si₃N₄ to β-Si₃N₄ could not be observed in the time and temperature range investigated. The crystallization process of amorphous Si₃N₄ can be described according to the Johnson–Mehl–Avrami–Kolmogorov (JMAK) formalism, assuming a three-dimensional, interface controlled grain growth from pre-existing nuclei. The rate constants show an Arrhenius behaviour with an activation enthalpy of approximately 5.5 eV.     

反应烧结制备Si3N4/SiC复相陶瓷及其力学性能研究

以两种不同配比Y₂O₃/Al₂O₃ (A, 2:3; B, 3:1, 总量15 wt%)为烧结助剂, 通过添加不同质量分数的SiC粉体,反应烧结制备了高强度的氮化硅/碳化硅复相陶瓷。并对材料的相组成、相对密度、显微结构和力学性能进行了分析。结果表明: 在1700℃保温2 h情况下, 烧结助剂A 与B对应的样品中α-Si₃N₄相全部转化为β-Si₃N₄; 添加5wt% SiC, 烧结助剂A对应样品的相对密度达到最大值94.8%, 且抗弯强度为521.8 MPa, 相对于不添加SiC样品的抗弯强度(338.7 MPa)提高了约54.1%。SiC能有效改善氮化硅基陶瓷力学性能, 且Si₃N₄/SiC复相陶瓷断裂以沿晶断裂方式为主。     

Effect of the microstructure of Si3N4 on the adhesion strength of TiN film on Si3N4

The effect of the microstructure of silicon nitride, which was used as a substrate, on the adhesion strength of physical vapor deposited TiN film on Si₃N₄ was investigated. Silicon nitride substrates with different microstructures were synthesized by controlling the size (fine or coarse), the phase ( or β) of starting Si₃N₄ powder, and sintering temperature. The microstructure of Si₃N₄ was characterized in terms of grain size, aspect ratio of the elongated grain, and β-to- phase ratio. For a given chemical composition but different mechanical properties, such as toughness, elastic modulus, and hardness of Si₃N₄ were obtained from the diverse microstructures. Hertzian indentation was used to estimate the yield properties of Si₃N_4, such as critical loads for yield (P_y) and for ring cracking (P_c). The effect of the microstructure of Si₃N₄ on adhesion strength evaluated by scratch test is discussed. TiN films on Si₃N₄ showed high adhesion strengths in the range of 80–140 N. Hardness and the P_y of Si₃N₄ substrate were the primary parameters influencing the adhesion strength of TiN film. In TiN coating on Si₃N₄, substrates with finer grain sizes and higher phase ratios, which show high hardness and high P_y, were suitable for higher adhesion strength of TiN film.     

复合烧结助剂对Si3N4陶瓷力学性能和热导率的影响

Si₃N₄陶瓷因兼具优异的力学和热学性能, 成为第三代半导体陶瓷基板的首选材料之一。本研究以7种不同离子半径的稀土氧化物(RE₂O₃, RE=Sc、Lu、Yb、Y、Gd、Nd、La)与非氧化物(MgSiN₂)作复合烧结助剂, 通过热压烧结和退火热处理制备了高强、高热导Si₃N₄陶瓷, 并系统研究了复合烧结助剂中RE₂O₃种类对Si₃N₄陶瓷物相组成、微结构、力学性能和热导率的影响规律。热压后Si₃N₄陶瓷力学性能优越, 其中添加Nd₂O₃-MgSiN₂的样品弯曲强度达到(1115±49) MPa。退火处理后Si₃N₄陶瓷的热导率得到大幅提升, 呈现出随稀土离子半径减小而逐渐增大的规律, 其中添加Sc₂O₃-MgSiN₂的样品退火后的热导率从54.7 W·m^-1·K^-1提升至80.7 W·m^-1·K^-1, 提升了47.6%。该结果表明, 相较于国际上通用的Y₂O₃-MgSiN₂和Yb₂O₃-MgSiN₂烧结助剂组合, Sc₂O₃-MgSiN₂有望成为制备高强度、高热导Si₃N₄陶瓷的新型复合助剂。     

氮化硼纳米管增强氮化硅复合材料的裂纹扩展阻力行为

用氮化硼纳米管(BNNT)增强氮化硅(Si₃N₄)陶瓷制备了BNNT/Si₃N₄复合材料, 利用三点弯曲强度及单边切口梁(SENB)法测定了BNNT/Si₃N₄复合材料的弯曲强度和断裂韧性。通过SEM观察了BNNT/Si₃N₄复合材料微观形貌。基于BNNT增强Si₃N₄陶瓷复合材料的裂纹扩展阻力计算公式, 构建了BNNT对Si₃N₄陶瓷裂纹屏蔽区的裂纹扩展阻力的数学模型。用该模型的计算结果与Si₃N₄陶瓷的裂纹扩展阻力进行了对比。结果表明: BNNT/Si₃N₄复合材料的弯曲强度和断裂韧性明显高于Si₃N₄陶瓷, 说明BNNT对Si₃N₄陶瓷的裂纹扩展有阻力作用, 摩擦拔出是Si₃N₄陶瓷抗裂纹扩展能力提高的主要原因; BNNT对Si₃N₄陶瓷有明显的升值阻力曲线行为。通过有限元模拟裂纹尖端应力分布, 发现BNNT使Si₃N₄陶瓷裂纹尖端的最大应力转移到纳米管上, 而且BNNT降低了Si₃N₄陶瓷裂纹尖端的应力, 对Si₃N₄陶瓷尖端的裂纹有屏蔽作用, 从而提高了Si₃N₄陶瓷的裂纹扩展阻力。     

反应烧结法制备高强度多孔氮化硅陶瓷

以硅粉(Si)为起始原料, 氧化钇(Y₂O₃)为烧结助剂, 利用干压成型工艺制备出不同气孔率的多孔硅坯体, 通过反应烧结得到高强度多孔氮化硅(Si₃N₄)陶瓷. 研究了Y₂O₃添加量在不同升温制度下对于氮化率的影响, 以及1500~1750℃后烧结对多孔材料强度的影响. 结果表明: 添加9%Y₂O₃的样品具有较高的氮化率, 主要是Y₂O₃与Si粉表面的SiO₂在较低的温度下反应生成了Y₅Si₃O₁₂N. 在不同的反应条件下可得到气孔率为30%~50%, 强度为160~50MPa的样品. 在1750、 0.5MPaN₂气压下对样品进行后处理, α-Si₃N₄完全转变成柱状β-Si₃N₄, 晶型转变有利于强度提高,气孔率为46%的多孔Si₃N₄其强度可达140MPa.     

Densification and grain growth during pressureless sintering of TiO2 nanoceramics

Anatase titania nanopowders with mean particle sizes of 7, 15, 26 and 38 nm synthesized by sol–gel method were used to sinter bulk TiO₂ nanoceramics. The relative densities and average grain sizes of the TiO₂ nanoceramics were studied as a function of the compaction pressure on green sheet, sintering temperature, and mean particle size of the starting TiO₂ nanopowders. The relative density of the TiO₂ nanoceramics increases rapidly and average grain size increases slowly with increasing sintering temperature below 800 °C. Sintering at higher temperatures above 800 °C enhances the densification of the TiO₂ nanoceramics and leads to a increase of the grain size. Bulk TiO₂ nanoceramics with an average grain size of less than 60 nm and relative density over 95% was obtained by a phase-transformation-assisted pressureless sintering at a relatively low temperature (800 °C).     

Interfacial microstructure and strength of partial transient liquid-phase bonding of silicon nitride with Ti/Ni multi-interlayer

Partial transient liquid-phase bonding (PTLP bonding) of silicon nitride (Si₃N₄) ceramic has been performed using Ti/Ni multi-interlayer in vacuum at 1273–1423 K. Interfacial microstructures were examined by scanning electron microscope, electron probe micro-analysis, and X-ray diffraction. The joint strength has been measured by four-point bending tests from room temperature up to 1000 °C. Interfacial structure of Si₃N₄/TiN/Ti₅Si₃ + Ti₅Si₄ + Ni₃Si/(NiTi)/Ni₃Ti/Ni is formed after bonding process. The NiTi layer is gradually consumed with simultaneous growth of the reaction layer and the Ni₃Ti layer. The room temperature joint strength is significantly affected by the reaction layer thickness, whereas the elevated temperature joint strength significantly depends on whether the low melting point NiTi layer exists in the joint. The joint strength of more than 100 MPa is retained up to 800 °C as the NiTi layer is completely consumed. A model is proposed to optimize the PTLP bonding parameters for optimizing joint strength at both room temperature and elevated temperature.     

Microwave dielectric characteristics of Ba(Mg1/3Ta2/3)O3 ceramics sintered at low-temperatures

The microwave dielectric properties and microstructures of Ba(Mg_1/3Ta_2/3)O₃ (BMT) ceramics sintered at low temperatures with 2–3 wt.% NaF additives were investigated. BMT ceramics sintered at 1340 °C for 3–12 h showed dielectric constants (_r) of 25.5–25.7, Qf values of 41 500–50 400 GHz and temperature coefficients of the resonator frequency (τ_f) of 10.9–21.4 ppm °C⁻¹. The variation of sintering time almost had no effect on the dielectric constant. The Qf value increased and the τ_f decreased with increasing sintering time. The ordering degree of Mg²⁺ and Ta⁵⁺ at B-sites increased with increasing sintering time.     

Si_3N_4原位增强Cu基复合材料的制备

采用感应炉熔炼及水雾化工艺制得了Cu-Si合金粉末,经N2、H2混合气体选择氮化和真空放电等离子烧结(SPS)成型,制备得到了Si3N4原位增强Cu基复合材料(Si3N4/Cu),利用萃取法研究了选择性氮化产物及其晶体结构。结果表明:复合粉末中N含量随氮化温度的升高和氮化时间的延长而增大。在1 000℃下氮化,持续时间大于60h时,粉末中的N含量明显提高;Cu的衍射峰出现整体向大角度方向的明显偏移,同时晶格常数变小,表明Si从Cu基体中脱溶,与N反应生成Si3N4;Si3N4/Cu复合材料的增强体以β-Si3N4为主;随着氮化温度的升高和氮化时间的延长,Si3N4/Cu复合材料的电导率和硬度逐步提高。     

浆料固相含量对数字光处理成形Si3N4陶瓷性能的影响

随着科技的不断发展, Si₃N₄陶瓷在航空、机械、生物医疗等高新领域发挥着越来越重要的作用。本工作采用包覆助烧剂Al₂O₃-Y₂O₃后的Si₃N₄粉体为原材料, 利用数字光处理(Digital light processing, DLP)技术成功制备出Si₃N₄陶瓷, 并系统研究了浆料固相含量对Si₃N₄陶瓷浆料、DLP成形Si₃N₄陶瓷素坯和陶瓷性能的影响。研究表明, 浆料固相含量低于40.0% (体积分数)时, 浆料在30 s^-1剪切速率下的粘度均小于2 Pa·s, 可用于DLP成形。在这种情况下, 浆料的单层固化深度随浆料固相含量的增加而减小。随着浆料固相含量的增大, DLP成形Si₃N₄陶瓷的相对密度和抗弯强度先升高后降低。固相含量为37.5% (体积分数)的样品获得最大的相对密度和抗弯强度, 分别为89.8%和162.5 MPa, 较固相含量为32.5% (体积分数)的样品分别提升了10%和16%。本研究通过对陶瓷浆料性能的优化, 提升了DLP成形Si₃N₄陶瓷的性能, 为Si₃N₄等非氧化物陶瓷光固化成形奠定了实验基础。     

Templated grain growth of SrBi2Ta2O9 ceramics: Mechanism of texture development

Textured SrBi₂Ta₂O₉ (SBT) ceramics were fabricated via templated grain growth (TGG) technique using platelet-like SBT single crystal templates. The templates (5 wt%) were embedded in a fine-grain SBT powder matrix containing 3 wt% of Bi₂O₃ excess that were subjected to uniaxial pressing and sintering at 1000–1250 °C for up to 24 h. Microstructural characterization by SEM was performed to establish the effect of sintering parameters on the grain growth and texture development. It was found that the ceramics developed a bimodal microstructure with notable concentration of large (longer than 90 μm) aligned grains with c-axis oriented parallel to the pressing direction. The mechanism controlling the texture development and grain growth in SBT ceramics is discussed.