六方氮化硼陶瓷的烧结及其结构与性能EI北大核心CSCD

以亚微米级h-BN粉体为原料,在不添加任何烧结助剂的情况下,分别采用无压烧结、热压烧结和放电等离子烧结（SPS）制备h-BN陶瓷,采用X射线衍射和扫描电子显微镜对烧结后样品的物相组成和显微结构进行测试和观察,研究不同烧结方法对h-BN陶瓷的致密度、晶粒取向、显微形貌及力学性能的影响,对比分析了不同烧结方法下坯体初始致密度对h-BN陶瓷性能的影响。结果表明：无压烧结无法实现h-BN陶瓷烧结致密化,力学性能较差,而通过热压和放电等离子烧结的方法均能得到结构致密、力学性能较好的h-BN陶瓷。相比于传统的无压和热压烧结,放电等离子烧结方法制备的h-BN陶瓷具有更高的致密度和更好的力学性能,而且晶粒更均匀细小,烧结温度可降低200℃以上。此外,坯体初始致密度的提高能显著提高h-BN陶瓷的抗弯强度和断裂韧性,但对热压和放电等离子烧结制备的h-BN陶瓷致密化的影响较小。     

国内放电等离子烧结技术的研究进展及展望

放电等离子烧结(SPS)技术是一种快速、低温、节能和环保的材料制备新技术。文章简要介绍SPS的基本概念、发展概况、烧结机理和特点,较详细叙述利用SPS工艺在研究开发功能梯度材料、特种陶瓷、电磁材料、硬质合金和纳米材料等方面的最新进展。展望了SPS技术的发展前景。     

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)。     

放电等离子烧结氮化铝透明陶瓷的研究

采用放电等离子烧结(spark plasma sintering，SPS)技术烧结氮化铝，在不加任何添加剂的条件下，1800℃，4～20min烧结制备了透明的氮化铝陶瓷。XRD，SEM，EPMA和TEM等测试结果表明，制备出的氮化铝陶瓷纯度较高、晶粒细小、结构均匀，具有良好的透光性能。充分说明SPS技术可应用于透明陶瓷的制备。与此同时，测试结果显示，AlN陶瓷中还含有少量的缺陷，包括位错、层错、气孔、第二相包裹体，这些缺陷无疑会对陶瓷的透光性能产生一定的影响。     

放电等离子烧结技术制备熔融石英陶瓷

以熔融石英陶瓷粉体为原料,采用放电等离子烧结(SPS)技术制备了熔融石英陶瓷材料。文章讨论了SPS方法制备熔融石英陶瓷材料的烧结行为和烧结机理,计算了熔融石英陶瓷的析晶温度并与实际测试结果进行了比较。结果表明:利用SPS方法,在短时间内其析晶温度在1150℃以上,且烧结温度为1150℃时,材料的致密度达到了99.7%,熔融石英的烧结是表层熔融烧结机制,烧结过程中压力对致密度的提高贡献很大。     

半透明氮化硅陶瓷的放电等离子烧结制备及性能

用放电等离子烧结(spark plasma sintering,SPS)技术,以质量分数(下同)为9%氮化铝(A1N),3%氧化镁(MgO)为烧结助剂,在1850℃烧结5min,成功制备了半透明氮化硅(Si3N4)陶瓷.半透明Si3N4陶瓷在中红外波段表现出良好的透过率,最大透过率为66.4%.SPS的快速致密化过程保证了烧结体具有良好的晶体结构,有利于提高透过率.SPS快速的烧结过程和A1N和MgO的加入能够有效抑制烧结过程中Si3N4陶瓷由α相向β相的转变,是制备光学性能良好的Si3N4陶瓷的关键.报道了半透明Si3N4陶瓷的其他性能.光学性能与其他性能的结合,势必大大拓宽Si3N4陶瓷的应用领域.     

TiB2陶瓷的放电等离子烧结

利用放电等离子烧结技术制备TiB2陶瓷。分析了烧结温度、保温时间和升温速率对烧结体致密度及显微结构的影响。实验结果表明：随着烧结温度的提高，烧结体的致密度及晶粒大小均增加。延长保温时间，样品的晶粒有明显长大。提高升温速率，有利于抑制晶粒生长，但样品的致密度降低。在TiB2的烧结过程中，存在颗粒间的放电。在烧结温度为1500℃，压力为30MPa，升温速率为100℃／min，真空中由SPS烧结制备的TiB2陶瓷相对密度可达98％。     

烧结工艺对Ca3Co4O9基热电氧化物电性能的影响

采用溶胶-凝胶化学法合成了Ca3Co4O9热电氧化物粉末,分别采用陶瓷烧结工艺方法和放电等离子烧结(Spark Plasma Sintering,SPS)的方法制备了Ca3Co4O9热电氧化物块体材料.利用X射线衍射XRD、扫描电子显微镜SEM和电输运参数测试仪分析了所得样品的物相、微观组织结构、晶粒取向度和电输运性能.结果表明,不同制备方法均可得到纯相的Ca3Co4O9热电氧化物块体材料;通过陶瓷烧结工艺方法制备的Ca3Co4O9热电氧化物块体晶粒取向度较低,但随着成型压力的增加而提高;SPS烧结的方法制备的Ca3Co4O9热电氧化物块体晶粒取向度最高;试样电性能随着晶粒取向度的提高逐渐提高,其中SPS烧结方法制备的块体材料电性能最高,在测试温度最高点700℃时功率因子达3.85 μWmK-2,远高于普通烧结试样.     

放电等离子烧结技术制备透明AlN陶瓷

采用放电等离子烧结(spark plasma sintering,SPS)技术,以CaF2为烧结助剂,在1850℃烧结15min,成功制备了透明AlN陶瓷。随着CaF2含量的增加,样品的密实度和透过率都随之提高。在CaF2含量为2．5％(质量分数)的AlN陶瓷样品的透光率最高(56．3％)。继续提高CaF2含量,样品密实度和透过率反而有所下降。SPS制备的纯AlN陶瓷样品中出现了颜色不均匀现象。与传统烧结方法比较,SPS制备的样品具有很高的致密度、纯度和良好的晶体结构。CaF2的加入降低了烧结温度,烧结时间短,提高了AlN陶瓷的透过率。是制备透明AlN陶瓷的有效烧结助剂。     

六方氮化硼陶瓷的烧结及其结构与性能

以亚微米级h-BN粉体为原料,在不添加任何烧结助剂的情况下,分别采用无压烧结、热压烧结和放电等离子烧结(SPS)制备h-BN陶瓷,采用X射线衍射和扫描电子显微镜对烧结后样品的物相组成和显微结构进行测试和观察,研究不同烧结方法对h-BN陶瓷的致密度、晶粒取向、显微形貌及力学性能的影响,对比分析了不同烧结方法下坯体初始致密度对h-BN陶瓷性能的影响。结果表明:无压烧结无法实现h-BN陶瓷烧结致密化,力学性能较差,而通过热压和放电等离子烧结的方法均能得到结构致密、力学性能较好的h-BN陶瓷。相比于传统的无压和热压烧结,放电等离子烧结方法制备的h-BN陶瓷具有更高的致密度和更好的力学性能,而且晶粒更均匀细小,烧结温度可降低200℃以上。此外,坯体初始致密度的提高能显著提高h-BN陶瓷的抗弯强度和断裂韧性,但对热压和放电等离子烧结制备的h-BN陶瓷致密化的影响较小。     

A Screening Design Approach for the Understanding of Spark Plasma Sintering Parameters: A Case of Translucent Polycrystalline Undoped Alumina

An experimental screening design was used to evaluate the effects of spark plasma sintering (SPS) parameters such as heating rate, sintering temperature, dwell duration, and green-shaping processing on the relative density, grain size, and the optical properties of polycrystalline alumina (PCA). It is shown that heating rate and sintering temperature are the most critical factors for the densification of PCA during SPS. Green-shaping processing could prevent grain growth at low SPS sintering temperatures. No predominant SPS parameters are observed on the optical properties. Hence, the optical properties of PCA are controlled by microstructural evolution during the SPS process.     

Hydroxyapatite/titania nanocomposites derived by combining high-energy ball milling with spark plasma sintering processes

Hydroxyapatite-reinforced nanocomposites with titania nanocrystals addition are prepared by a homogeneous mixing of hydroxyapatite nanoparticles and titania nanocrystals based on high-energy ball milling and spark plasma sintering processes. The microstructural and mechanical properties of the HA/titania composites are studied by X-ray diffractometry analysis, Raman spectrometry, and scanning electron microscopy. The hardness and Young's modulus of the composites are characterized by a nanoindenter and they show that the incorporation of the titania nanocrystals improves the mechanical properties of the composites obviously and the improvement should be ascribed to the main solitary effect of the ceramic as additives as well as a denser composites due to combining high-energy ball milling with spark plasma sintering techniques. The bioactivity of the HA/titania composites is evaluated by immersing the spark plasma sintering (SPS) compact disk in the simulated body fluid (SBF) and the results indicate that the bioactivity of the composites is related to the addition of titania by inducing apatite nucleation on the sample's surface after being immersed in SBF.     

Microstructure-mechanical-tribological property correlation of multistage spark plasma sintered tetragonal ZrO2

We report here the development of dense yttria-stabilized t-ZrO₂ ceramics with more uniform and finer grain sizes and concomitantly better mechanical and tribological properties via multistage spark plasma sintering (SPS). The dense tetragonal ZrO₂ ceramics were obtained by adopting three different SPS heating cycles, designed on the basis of fundamental sintering theory. The suppression of grain growth to nanosize regime (～100–150 nm), along with the development of more uniform grain size distribution was achieved with multistage sintering (MSS), as compared to normal single stage sintering (SSS). Finer microstructural scale, along with superior hardness also led to improved fretting wear resistance for the ZrO₂ samples processed via MSS. Based on the experimental results and analysis, a correlation has been established between the SPS processing schemes, microstructural development and mechanical as well as tribological properties of the tetragonal ZrO₂. The effectiveness of MSS to produce tetragonal ZrO₂ ceramics with better mechanical and tribological properties was confirmed at two different levels of yttria content (3 and 2 mol%).     

放电等离子烧结La0.67Sr0.33MnO3-δ粉体的输运性质

用自蔓延高温合成技术合成La0.67Sr0.33MnO3-δ粉体.探讨了放电等离子烧结的烧结温度对合成粉体的显微结构和输运性质的影响.扫描电镜和密度测试结果表明:放电等离子烧结后的晶粒大小均匀,烧结体致密度高.随着烧结温度的升高,样品的电阻率明显下降.由于氧缺位的存在,金属-绝缘相转变温度随着烧结温度的升高而降低.相对于传统的固相烧结,放电等离子工艺制得的样品的致密度较高导致颗粒间的巨磁电阻有所提高.     

掺杂Sb2O3的SnO2基陶瓷的SPS制备及性能研究

采用放电等离子烧结技术(SPS)制备了掺Sb2O3的SnO2基陶瓷.研究了烧结温度及Sb2O3的含量对SnO2基陶瓷的密度、物相、结构和电学性能的影响.研究袭明:随着烧结温度的提高,SnO2基陶瓷的相对密度逐渐增大,室温电阻率璧先减小后增大的趋势;随着Sb2O3掺杂量的增加,样品的相对密度呈先增加后减小的趋势,室温电阻...     

Effect of sintering temperature on the structural and magnetic properties of MgFe2O4 ceramics prepared by spark plasma sintering

Spark plasma sintering (SPS) is a powerful technique to produce fine grain dense ferrite at low temperature. This work was undertaken to study the effect of sintering temperature on the densification, microstructures and magnetic properties of magnesium ferrite (MgFe₂O₄). MgFe₂O₄ nanoparticles were synthesized via sol–gel self-combustion method. The powders were pressed into pellets which were sintered by spark plasma sintering at 700–900 °C for 5 min under 40 MPa. A densification of 95% of the theoretical density of Mg ferrite was achieved in the spark plasma sintered (SPSed) ceramics. The density, grain size and saturation magnetization of SPSed ceramics were found to increase with an increase in sintering temperature. Infrared (IR) spectra exhibit two important vibration bands of tetrahedral and octahedral metal-oxygen sites. The investigations of microstructures and magnetic properties reveal that the unique sintering mechanism in the SPS process is responsible for the enhancement of magnetic properties of SPSed compacts.     

Spark plasma sintering and hot pressing of ZTA-NbC materials – A comparison of mechanical and electrical properties

Zirconia toughened alumina can be made electrically conductive and thus electric discharge machinable by addition of a percolating dispersion of niobium carbide. In order to boost the productivity of the sintering process spark plasma sintering was tested at identical temperature and pressure but shorter dwell than in hot pressing. SPS sintering parameters for ZTA-NbC are developed and spark plasma sintered ceramics are compared to the hot pressed benchmark.During SPS a percolating NbC backbone of niobium carbide grains is formed which enhances electrical conductivity but impedes densification. Identical strength at however higher sintering temperature is achieved by SPS but the fracture resistance and hardness were always superior in hot pressed samples. The monoclinic content of zirconia grains in as fired SPS samples is higher despite smaller average grain size and the transformation toughening effect is less pronounced. SPS promises economic benefits due to shorter dwell and cooling cycles.     

Sintering behavior and mechanical properties of spark plasma sintering SiO2-MgO ceramics

SiO₂-MgO ceramics containing different weight fractions (0, 0.5, 1, 2, and 4 wt%) of SiO₂ powder were prepared by mixing nano MgO powder, and the powder mixtures were densified by spark plasma sintering (SPS). The effect of SiO₂ addition and SPS method on the sintering behavior, microstructure and mechanical properties were investigated. Results were compared to specimens obtained by conventional hot pressing (HP) under a similar sintering schedule. The highest relative density, flexural strength and hardness of 2 wt% SiO₂-MgO ceramics reached 99.98%, 253.99 ± 7.47 MPa and 7.56 ± 0.21 GPa when sintered at 1400 °C by SPS, respectively. The observed improvement in the sintering behavior and mechanical properties are mainly attributed to grain boundary "strengthening" and intragranular "weakening" of the MgO matrix. Furthermore, the spark plasma sintering temperature could be decreased by more than 100 °C as compared with the HP method, SPS favouring enhanced grain boundary sliding, plastic deformation and diffusion in the sintering process.     

Consolidation of Nano-Sized TiN Powders by Spark Plasma Sintering

Nano-sized TiN powders with an average particle size of 19 nm were synthesized via a new method, reduction–nitridation reaction in liquid ammonia. A consolidation procedure using spark plasma sintering (SPS) was used, and a dense TiN ceramic (>98% of theoretical) with mean grain size of 100–150 nm was obtained at 1380°C. The influence of sintering temperature on grain growth and microstructural evolution was also discussed.     

Sintering resistance of advanced plasma-sprayed thermal barrier coatings with strain-tolerant microstructures

Sintering is one of the key issues in the high temperature service of thermal barrier coatings (TBCs), considering the continuously increasing operation temperature of gas-turbine for higher energy efficiency. Based on the conventional processing method of air plasma spraying (APS), suspension plasma spraying (SPS) technique has been developed recently, in order to improve the strain tolerance of TBCs. This strain tolerance of plasma-sprayed TBCs is largely effected by the sintering behavior, which is presently not fully understood. In this work, evolution of mechanical properties, in terms of Young’s modulus and viscosity, is systematically investigated by in-situ three-point bending test at 1200?°C on free-standing coatings, including micro-cracked APS, segmented APS, vertically cracked SPS and columnar structured SPS TBCs and correlated to the microstructural evolution. Based on experimental results, power law relations are proposed for the sintering induced mechanical evolution, which deepen the understanding of the sintering behavior of plasma-sprayed TBCs.