(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.     

Small amount TiB2 addition into B4C through sputter deposition and hot pressing

Small amount of TiB₂ (<5 wt%) was added into B₄C through a novel method that combines the use of sputter deposition and hot pressing. Sputter deposition provided more uniform dispersion of TiB₂ grains with smaller grain sizes as compared to the conventional particulate mixing. Small amount TiB₂ addition demonstrated to be an effective way for improving the fracture behavior and toughness of B₄C while not sacrificing its outstanding lightweight property to a large extent: 2.3 wt% TiB₂ addition brought 15% improvement in indentation fracture toughness while resulting in less than 2% increase in density. The improvement can be attributed to the combination of crack impeding by TiB₂ grains and crack deflection at the B₄C–TiB₂ interfaces. TiB₂ also played as grain growth inhibitor resulting in a slight increase (2%) in Vickers hardness. Another intention of employing sputter deposition was to modify the grain boundary of B₄C; however, neither formation of Ti-containing phase nor Ti segregation has been observed at grain boundaries likely due to the poor wettability of B₄C.     

Synthesis and properties of conductive B4C ceramic composites with TiB2 grain network

High electrical resistance and low fracture toughness of B₄C ceramics are 2 of the primary challenges for further machining of B₄C ceramics. This report illustrates that these 2 challenges can be overcome simultaneously using core‐shell B₄C‐TiB₂&TiC powder composites, which were prepared by molten‐salt method using B₄C (10 ± 0.6 μm) and Ti powders as raw materials without co‐ball milling. Finally, the near completely dense (98%) B₄C‐TiB₂ interlayer ceramic composites were successfully fabricated by subsequent pulsed electric current sintering (PECS). The uniform conductive coating on the surface of B₄C particles improved the mass transport by electro‐migration in PECS and thus enhanced the sinterability of the composites at a comparatively low temperature of 1700°C. The mechanical, electrical and thermal properties of the ceramic composites were investigated. The interconnected conductive TiB₂ phase at the grain boundary of B₄C significantly improved the properties of B₄C‐TiB₂ ceramic composites: in the case of B₄C‐29.8 vol% TiB₂ composite, the fracture toughness of 4.38 MPa·m^1/2, the electrical conductivity of 4.06 × 10⁵ S/m, and a high thermal conductivity of 33 W/mK were achieved.     

热压烧结制备原位复合（TiB2+TiC）/Ti3SiC2复相陶瓷

采用热压烧结法制备了原位复合(TiB2+TiC)/Ti3SiC2复相陶瓷。采用X射线衍射、扫描电镜和透射电镜对材料的物相组成和显微结构进行了表征,研究了烧结温度对材料物相组成、烧结性能、显微结构与力学性能的影响。结果表明:烧结温度在1 350～1 500℃范围内,随着烧结温度的升高,合成反应进行逐渐完全,材料的密度、抗弯强度和断裂韧性显著提高。1 500℃烧结可得到致密的原位复合(TiB2+TiC)/Ti3SiC2复相陶瓷,材料晶粒发育较完善,层片状Ti3SiC2、柱状TiB2与等轴状TiC晶粒清晰可见,增强相晶粒细小,晶界干净,材料的抗弯强度、断裂韧性和Vickers硬度分别达到741 MPa,10.12 MPa.m1/2和9.65 GPa。烧结温度达到1 550℃时Ti3SiC2开始发生分解,材料的密度和力学性能又显著下降。     

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.     

Elevated temperature thermal properties of ZrB2-B4C ceramics

The elevated temperature thermal properties of zirconium diboride ceramics containing boron carbide additions of up to 15 vol% were investigated using a combined experimental and modeling approach. The addition of B₄C led to a decrease in the ZrB₂ grain size from 22 µm for nominally pure ZrB₂ to 5.4 µm for ZrB₂ containing 15 vol% B₄C. The measured room temperature thermal conductivity decreased from 93 W/m·K for nominally pure ZrB₂ to 80 W/m·K for ZrB₂ containing 15 vol% B₄C. The thermal conductivity also decreased as temperature increased. For nominally pure ZrB₂, the thermal conductivity was 67 W/m·K at 2000 °C compared to 55 W/m·K for ZrB₂ containing 15 vol% B₄C. A model was developed to describe the effects of grain size and the second phase additions on thermal conductivity from room temperature to 2000 °C. Differences between model predictions and measured values were less than 2 W/m·K at 25 °C for nominally pure ZrB₂ and less than 6 W/m·K when 15 vol% B₄C was added.     

利用碳化稻壳原位合成SiC-B4C复合陶瓷粉的研究

为了稻壳更好地被回收利用,以硼酸、石油焦为原料,碳化稻壳为添加剂,采用碳热还原法经1800℃保温50 min原位合成SiC-B 4C复合陶瓷粉(A类试样),研究不同碳化稻壳的添加量(质量分数分别为2.42%、4.96%、7.69%、10.57%和13.61%)对烧后A类试样的相组成、表观形貌、粒度大小的影响;并与B 4C和SiC机械混合制备SiC-B 4C复合陶瓷粉(B类试样)的进行了对比。结果表明:原位合成和机械混合均制备了含B 4C和SiC的复合陶瓷粉;碳化稻壳的添加量为4.96%(w)时,B 4C与SiC物相的衍射峰强度均较高,晶粒生长状况较好,粒度相对最细,d 50=7.624μm;原位合成相比机械混合制备的试样在晶粒界面结合方面存在明显的优势。     

Addressing amorphization and transgranular fracture of B4C through Si doping and TiB2 microparticle reinforcing

Over the last two decades, many studies have contributed to improving our understanding of the brittle failure mechanisms of boron carbide and provided a road map for inhibiting the underlying mechanisms and improving the mechanical response of boron carbide. This paper provides a review of the design and processing approaches utilized to address the amorphization and transgranular fracture of boron carbide, which are mainly based on what we have found through 9 years of work in the field of boron carbides as armor ceramics.     

大力发展硼化物金属陶瓷

介绍了碳化硼、氮化硼、二硼化钛三种硼化物金属陶瓷材料,由于其具有耐高温、耐磨、耐腐蚀等特殊性能,在国民经济多个领域有着广泛的应用前景。     

Fracture and property relationships in the double diboride ceramic composites by spark plasma sintering of TiB2 and NbB2

Bulk titanium diboride–niobium diboride ceramic composites were consolidated by spark plasma sintering (SPS) at 1950°C. SPS resulted in dense specimens with a density exceeding 98% of the theoretical density and a multimodal grain size ranging from 1 to 10 μm. During the SPS consolidation, the pressure was applied and released at 1950 and 1250°C, respectively. This allowed obtaining a two-phase composite consisting of TiB₂ and NbB₂. For these ceramics composites, we evaluated the flexural strength and fracture toughness and room and elevated temperatures. Room-temperature strength of thus produced bulks was between 300 and 330 MPa, at 1200°C or 1600°C an increase in strength up to 400 MPa was observed. Microstructure after flexure at elevated temperatures revealed the appearance of the needle-shape subgrains of NbB₂, an evidence for ongoing plastic deformation. TiB₂–NbB₂ composites had elastic loading stress curves at 1600°C, and at 1800°C fractured in the plastic manner, and strength was ranged from 300 to 450 MPa. These data were compared with a specimen where a (Ti,Nb)B₂ solid solution was formed during SPS to explain the behavior of TiB₂–NbB₂ ceramic composites at elevated temperatures.     

TiB2系金属陶瓷的SHS—QP制备

从理论和试验上对ＴｉＢ２－ｘＦｅ复合体系的ＳＨＳ过程参数进行分析。计算得到ＴｉＢ２－４０％Ｆｅ（以摩尔计）的ＳＨＳ过程激活能为３９９ｋＪ／ｍｏｌ，接近Ｔｉ＋２Ｂ在燃烧温度区域的反应过程激活能，预示着一种扩散控制机理。进行了ＳＨＳ－ＱＰ技术制备密实金属陶瓷的研究，包括加压延迟、压力延续和压力大小等参数对产品密实度的影响。通过优化和控制有关参数，制备出了良好力学性能的金属陶瓷，为金属陶瓷的制备提供了新     

High-strength TiB2-B4C composite ceramics sintered by spark plasma sintering

Spark plasma sintering (SPS) is an advanced sintering technique because of its fast sintering speed and short dwelling time. In this study, TiB₂, Y₂O₃, Al₂O₃, and different contents of B₄C were used as the raw materials to synthesize TiB₂-B₄C composites ceramics at 1850°C under a uniaxial loading of 48 MPa for 10 min via SPS in vacuum. The influence of different B₄C content on the microstructure and mechanical properties of TiB₂-B₄C composites ceramics are explored. The experimental results show that TiB₂-B₄C composite ceramic achieves relatively good comprehensive properties and exceptionally excellent flexural strength when the addition amount of B₄C reaches 10 wt.%. Its relative density, Vickers hardness, fracture toughness, and flexural strength reach to 99.20%, 24.65 ± .66 GPa, 3.16 MPa·m^1/2, 730.65 ± 74.11 MPa, respectively.     

B4C–TiB2 composites fabricated by hot pressing TiC–B mixtures: The effect of B excess

Previous research have reported that B₄C–TiB₂ composites could be prepared by the reactive sintering of TiC–B powder mixtures. However, due to spontaneous oxidation of raw powders, using TiC–B powder mixtures with a B/TiC molar ratio of 6: 1 introduced an intermediate phase of C during the sintering process, which deteriorated the hardness of the composites. In this report, the effects of B excess on the phase composition, microstructure, and mechanical properties of B₄C–TiB₂ composites fabricated by reactive hot pressing TiC–B powder mixtures were investigated. XRD and Raman spectra confirmed that lattice expansion occurred in B-rich boron carbide and B_xC–TiB₂ (x > 4) composites were obtained. The increasing B content improved the hardness and fracture toughness but decreased the flexural strength of B_xC–TiB₂ (x > 4) composites. When the molar ratio of B/TiC increased from 6.6:1 to 7.8:1, the Vickers hardness and the fracture toughness of the composites were enhanced from 26.7 GPa and 4.53 MPa m^1/2 to 30.4 GPa and 5.78 MPa m^1/2, respectively. The improved hardness was attributed to the microstructural improvement, while the toughening mechanism was crack deflection, crack bridging and crack branching.     

Growth behavior of TiB2 hexagonal plates prepared via a molten-salt-mediated carbothermal reduction

TiB₂ powders were successfully synthesized by a molten-salt-mediated carbothermal reduction method. The products obtained at 1300°C for 2 hours were hexagonal plates with side length of 3-8 μm and thicknesses of 200-500 nm. The microstructural evolution with temperature confirmed that the growth of TiB₂ hexagonal plates was a layer-by-layer growth controlled by a two-dimensional nucleation. No-uniform grains were observed attached on side and step edges of TiB₂ plates, which became finer and disappeared during the growth. This indicated that layer growth and growth on the side of TiB₂ plates followed the surface adsorption growth model.     

Synthesis of TiB2 from a carbon‐coated precursors method

This article deals with the synthesis of TiB₂ from carbon‐coated TiO₂ precursors with the addition of B₄C. The carbon‐coated precursors method alters the reaction process, compared with the conventional mixing of reactants, to produce high‐quality TiB₂ powders. The produced powders have a single phase, a submicron particle size (~0.3 to 0.8 μm), regular shape, loose agglomeration, and low level of contaminations (less than 0.5 wt% carbon and 0.6 wt% oxygen). The formation mechanism proposed is based on experimental results and thermodynamic evaluations. For comparison, the powders obtained from the mixture of reactants show higher agglomeration, a large particle size (>1 μm), high level of contaminations (0.7 wt% carbon and 1.1 wt% oxygen), and difficulty to control the reaction process (formation of TiBO₃ and Ti₂O₃ as the intermediate phases). The synthesized powders from the precursors method can be hot pressed to a relative density of ~94.5% with the formation of platelike grains at 1800°C under a pressure of 35 MPa without additives.     

溶胶-凝胶法制备固载型光催化剂TiO2膜的试验研究

研究了溶胶-凝胶法制备负载于玻璃上的光催化剂TiO2膜的制备条件：包括溶胶的体系组成、溶胶溶液的pH值及TiO2膜的焙烧温度。用X射线衍射和扫描电镜对制备的TiO2膜的物相和形貌进行了表征。     

二硼化钛在氟化钾溶液中的放电行为

研究了二硼化钛电极在20%(质量分数)KF溶液中的放电性能及其影响因素。试验发现,当放电速率为100 mA/g时,二硼化钛电极总的放电容量可达2000 mA.h/g。二硼化钛电极在20%(质量分数)KF溶液中的放电曲线上出现了4个放电平台,结合循环伏安曲线、ICP及XRD等分析手段对相应的电化学过程进行了分析,提出了二硼化钛发生电化学氧化反应的可能机理。     

锆英石碳热还原制备ZrB2-ZrO2-SiC复合粉体

以锆英石、硼酸和炭黑为原料，在流通氩气气氛中于1 500℃煅烧制备ZrB₂-ZrO₂-SiC复合粉体，研究了保温时间（分别为3、6和9 h）和添加剂AlF₃添加量（质量分数分别为0、0.5%、1.0%、1.5%、2.0%和2.5%）对合成产物物相组成和显微结构的影响。结果表明：1)将锆英石在流通氩气气氛中于1 500℃碳热还原可制备ZrB₂-ZrO₂-SiC复合粉体；ZrB₂、ZrO₂呈粒状，SiC呈纤维状。2)随着保温时间的延长，ZrB₂的量逐渐增多，m-ZrO₂和SiC的量均逐渐减少，非氧化物ZrB₂、SiC、ZrC的总量逐渐增多。3)与未添加AlF₃的试样相比，添加0.5%（w）AlF₃的试样中m-ZrO₂量显著减少，ZrB₂的量显著增多，SiC的量有所减少；但随着AlF     

氧化铝-莫来石复合粉对莫来石烧结行为的影响

将莫来石先驱体溶胶预先引入到硫酸铝水溶液中 ,干燥后经 12 0 0℃煅烧获得氧化铝 -莫来石复合粉料。研究了该粉料与硅溶胶混合获得的混合粉的烧结行为 ,并与氧化铝、莫来石晶种和硅溶胶三相混合获得的混合粉的烧结行为进行了分析比较。其中 ,两种混合粉料均是以理论莫来石组分进行配比 (Al2 O3∶SiO2 =72∶2 8) ,并且两种混合粉中莫来石晶种的质量分数均为 5%。实验结果表明 :前者在 1450℃烧结 2 0min即实现完全莫来石化 ,其显微结构为晶须状莫来石 ;后者在 150 0℃烧结 2 0min实现完全莫来石化 ,其显微结构为针状莫来石     

High‐Strength B4C–TaB2 Eutectic Composites Obtained via In Situ by Spark Plasma Sintering

The in situ synthesis/consolidation of B₄C–TaB₂ eutectic composites by spark plasma sintering (SPS) is reported. Samples for the evaluation of bending strength were cut from specimens with diameters of 30 mm. The sample prepared for the three‐point flexural strength test had fibers of tantalum diboride with diameter of 1.3 ± 0.4 μm distributed in the B₄C matrix, thereby reducing composites brittleness and yielding an indentation fracture toughness of up to 4.5 MPa·m^1/2. Furthermore, the Vickers hardness of B₄C–TaB₂ eutectics formed by SPS was as high as 26 GPa at an indentation load of 9.8 N. The flexural strength of the B₄C–TaB₂ system has been reported for the first time. Some steps were identified in the load–displacement curve, suggesting that micro‐ and macrocracking occurred during the flexural test. Ceramic composites with a eutectic structure exhibited a room‐temperature strength of 430 ± 25 MPa. Compared with other eutectic composites of boron carbide with transition‐metal diborides, room‐temperature strength the B₄C–TaB₂ was 40% higher than that of B₄C–TiB₂ ceramics, demonstrating advantage of the in situ synthesis/consolidation of eutectic composites by SPS.