High‐temperature strength and plastic deformation behavior of niobium diboride consolidated by spark plasma sintering

Bulk niobium diboride ceramics were consolidated by spark plasma sintering (SPS) at 1900°C. SPS resulted in dense specimens with a density of 98% of the theoretical density and a mean grain size of 6 μm. During the SPS consolidation, the hexagonal boron nitride (h‐BN) was formed from B₂O₃ on the powder particle surface and residual adsorbed nitrogen in the raw diboride powder. The room‐temperature strength of these NbB₂ bulks was 420 MPa. The flexural strength of the NbB₂ ceramics remained unchanged up to 1600°C. At 1700°C an increase in strength to 450 MPa was observed, which was accompanied by the disappearance of the secondary h‐BN phase. Finally, at 1800°C signs of plastic deformation were observed. Fractographic analysis revealed a number of etching pits and steplike surfaces suggestive of high‐temperature deformation. The temperature dependence of the flexural strength of NbB₂ bulks prepared by SPS was compared with data for monolithic TiB₂, HfB₂ and ZrB₂. Our analysis suggested that the thermal stresses accumulated during SPS consolidation may lead to additional strengthening at elevated temperatures.     

Al2O3／TiB2陶瓷材料的高温摩擦磨损特性研究

研究了Ａｌ２Ｏ３／ＴｉＢ２陶瓷材料与硬质合金往复滑动摩擦时，在不同氢气和温度条件下的摩擦磨损特性，结果表明：随温度和气氛不同，材料的摩擦系数有着不同的变化规律。在高温空气气氛中摩擦时，ＴｉＢ２氧化生成的表面氧化膜可起到固体润滑剂的作用，并且能阻止Ｃｏ的扩用，减轻粘着，因而能降低摩擦系数并有利于提高材料的耐磨性能；而在高温氮气气氛中摩擦时，由于硬质合金中的Ｃｏｐ扩散到陶瓷材料中，使材料产生粘着磨损和     

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.     

Spark plasma sintering of B4C and B4C-TiB2 composites: Deformation and failure mechanisms under quasistatic and dynamic loading

Spark plasma sintering (SPS) was employed to consolidate powder specimens consisting of B₄C and various B₄C-TiB₂ compositions. SPS allowed for consolidation of pure B₄C, B₄C-13 vol.%TiB₂, and B₄C-23 vol.%TiB₂ composites achieving ≥99 % theoretical density without sintering additives, residual phases (e.g., graphite), and excessive grain growth due to long sintering times. Electron and x-ray microscopies determined homogeneous microstructures along with excellent distribution of TiB₂ phase in both small and larger-scaled composites. An optimized B₄C-23 vol.%TiB₂ composite with a targeted low density of ～3.0 g/cm³ exhibited 30–35 % increased hardness, fracture toughness, and flexural bend strength compared to several commercial armor-grade ceramics, with the flexural strength being strain rate insensitive under quasistatic and dynamic loading. Mechanistic studies determined that the improvements are a result of a) no residual graphitic carbon in the composites, b) interfacial microcrack toughening due to thermal expansion coefficient differences placing the B₄C matrix in compression and TiB₂ phase in tension, and c) TiB₂ phase aids in crack deflection thereby increasing the amount of intergranular fracture. Collectively, the addition of TiB₂ serves as a toughening and strengthening phase, and scaling of SPS samples show promise for the manufacture of ceramic composites for body armor.     

（Nb，Ti）C－35Ni金属陶瓷的高温抗弯强度

对热等静压方法制备的（Ｎｂ，Ｔｉ）Ｃ－３５Ｎｉ金属陶瓷的高温抗弯强度进行了研究。采用ＸＲＤ，ＳＥＭ及ＴＥＭ等方法对该金属陶瓷的显微结构作了分析。结果表明，在氧化气氛中，温度为７００℃时该金属陶瓷的抗弯强度就明显下降，温度为１０００℃时其抗弯强度约只有室温时的２０％。     

温度对晶须增韧陶瓷刀具材料力学性能的影响——Ⅰ高温抗弯强度的研究

采用两种不同尺寸的试件,在室温～1000℃范围内,对SiC晶须增韧Al_2O_3陶瓷刀具材料JX-1的高温抗弯强度进行了测试。结果表明,在600℃之前,抗弯强度值变化很小,大约在800℃左右出现一个峰值,随着温度的继续升高,抗弯强度显著下降。试件断口的SEM分析表明,在较低温度下,断口表现出较多的穿晶断裂的特征;而在较高温度下,则以沿晶断裂为主。作者认为晶须与基体的热胀系数、泊松比及晶须与基体界面的摩擦系数均是影响陶瓷材料高温抗弯强度的重要因素。     

Low‐temperature preparation of titanium diboride fine powder via magnesiothermic reduction in molten salt

Phase pure titanium diboride (TiB₂) powder of 100‐200 nm was synthesized from TiO₂ and B₂O₃ using a molten‐salt‐assisted magnesiothermic reduction technique. The effects of salt type, Mg amount, reaction temperature, and TiO₂ raw materials on the synthesis process were examined and the relevant reaction mechanisms discussed. Among the three chloride salts (NaCl, KCl, and MgCl₂), MgCl₂ showed the best accelerating‐effect. To synthesize phase pure TiB₂, 20 mol% excessive Mg had to be used to compensate for the evaporation loss of Mg. Particle shape and size of raw material TiO₂ showed little effect on the formation of TiB₂ and its shape and size, suggesting that relatively cheaper and coarser TiO₂ raw materials could be used for low‐temperature synthesis of TiB₂ fine particles. The “dissolution‐precipitation” mechanism governed the overall molten salt synthesis process.     

(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.     

Simultaneous Synthesis and Densification of Titanium Nitride/ Titanium Diboride Composites by High Nitrogen Pressure Combustion

Composites of TiN/TiB₂ were synthesized by a combustion process of BN, Ti in a nitrogen atmosphere. The effect of the BN/Ti ratio and the nitrogen gas pressure on the synthesis of these composites was investigated. Dense TiN/TiB₂ composites with relatively high hardness and toughness were fabricated by combustion synthesis from Ti and BN under a nitrogen pressure of 4.0 MPa. The Vickers microhardness of the products obtained from reactants with a BN/Ti mole ratio of 0.11 increased with an increase in nitrogen pressure and had a maximum value of ∼25 GPa. Fracture toughness, K _IC, of the products increased from 3.1 to 5.9 MPa·m^1/2 as the BN/Ti ratio increased from 0.11 to 0.20. However, products formed under nitrogen pressures higher than 6.0 MPa exhibited circumferential macrocracks due to thermal shock.     

Al2O3陶瓷基体中原位生成TiB2和Ti（C,N）研究

采用原位反应法结合热压工艺制备Ａｌ２Ｏ３－ＴｉＢ２－Ｔｉ（Ｃ，Ｎ）复相陶瓷，用ＴｉＯ２，Ｂ４Ｃ，ＢＮ，Ａｌ及Ａｌ２Ｏ３为原料，通过组成设计可以制备出不同相组成及碳氮比的复相陶瓷。由ＳＥＭ及ＴＥＭ发现在Ａｌ２Ｏ３晶粒中分布着亚微米至微米级的近圆形Ｔｉ（Ｃ，Ｎ）颗粒，而在ＴｉＢ２晶粒中分布着纳米级的板状Ｔｉ（Ｃ，Ｎ）晶体，并对这种显微结构的形成机理及化学反应过程作用初步分析。     

Synthesis of Dense TiB2-TiN Nanocrystalline Composites through Mechanical and Field Activation

The synthesis of dense nanometric composites of TiN-TiB₂ by mechanical and field activation was investigated. Powder mixtures of Ti, BN, and B were mechanically activated through ball milling. Some powders were milled to reduce crystallite size but to avoid initiating a reaction. In other cases powders were milled and allowed to partially react. All these were subsequently reacted in a spark plasma synthesis (SPS) apparatus. The products were composites with equimolar nitride and boride components with relative densities ranging from 90.1% to 97.2%. Crystallite size analyses using the XRD treatments of Williamson-Hall and Halder-Wagner gave crystallite sizes for the TiN and TiB₂ components in the range 38.5–62.5 and 31.2–58.8 nm, respectively. Vickers microhardness measurements (at 2 N force) on the dense samples gave values ranging from 14.8 to 21.8 GPa and fracture toughness determinations (at 20 N) resulted in values ranging from 3.32 to 6.50 MPa·m^1/2.     

Wetting,reactivity, and phase formation at interfaces between Ni–Al melts and TiB2 ultrahigh‐temperature ceramic

The wetting, reactivity, and phase formation at the liquid Ni–Al/TiB₂ ceramic interfaces have been investigated at the temperatures close to the Ni–Al liquidus line. The wetting kinetics has been studied by the sessile drop technique utilizing liquid drop dispension and high‐speed high‐resolution video imaging. It is established that the wetting behavior changes from a nonreactive for the Al‐rich melts to a dissolution‐reactive for the Ni‐rich melts. For the Ni concentration ≥40 at.%, TiB₂ precipitates are found in the solidified Ni–Al droplets after the high‐temperature interaction of the melts with TiB₂ substrates. Besides, new (Al,Ti)Ni₃ and (Al,Ti)₂Ni₂₁B₆ phases are formed due to dissolution of TiB₂ ceramic in Ni‐rich melts and subsequent solidification.     

碳化硅—二硼化钛系多层陶瓷复合材料的制取与性能

介绍了制取多层陶瓷用的材料和方法 ,讨论了一些因素对材料性能的影响 ,并给出了几种复合材料的组成     

原位合成碳化硅-硼化钛复相陶瓷的高温摩擦性能及其磨损机理

以SiC为基体,用TiC和B4C为原料反应生成TiB2,原位合成了SiC-TiB2复相陶瓷.通过测试SiC和SiC-TiB2的高温摩擦系数和比磨损率与温度、外加载荷的关系,研究了SiC-TiB2复相陶瓷的高温摩擦学性能.在空气中,外加载荷为0.2 MPa,摩擦速度为0.3 m/s时,SiC-TiB2复相陶瓷自对偶(SiC-TiB2/SiC-TiB2)高温摩擦呈现较好的高温自润滑性能.温度对SiC-TiB2/SiC-TiB2摩擦系数和比磨损率的影响与载荷有关.载荷为0.4 MPa时,比磨损率最大.用X射线衍射测试了SiC-TiB2/SiC-TiB2磨屑的组成,用扫描电子镜观察了SiC-TiB2/SiC-TiB2磨损断面,发现高温摩擦氧化是TiB2-SiC/SiC-TiB2磨损的主要机理.磨损断面包含摩擦氧化层、过渡层和基体亚表面3层,氧化层和过渡层接触紧密.磨屑具有典型包裹结构,其主要氧化物是无定形氧化硅.平滑的氧化层改进了摩擦表面的塑变性能,缓冲了摩擦应力,减小了高温比磨损率.     

原位合成Si3N4／BN纤维独石陶瓷高温强度的研究

本实验对原位合成的Si3N4/BN纤维独石高温强度的力学性能进行了研究,实验结果表明：Si3N4/BN纤维独石陶瓷具有优异的高温力学性能。单轴排布的纤维独石陶瓷随温度的升高,直至1000℃,抗弯强度基本没有下降。到1200℃,强度还保持在600MPa以上,为室温强度的85％,实验通过扫描电镜SEM观察了材料的显微以及断口形貌,并对此材料具有优异的高温抗弯强度的机理进行了探索。     

TiB_2材料的研究现状及其应用

ＴｉＢ_２材料具有熔点高、硬度大、耐磨、耐腐蚀、抗氧化性、导电性和导热性好等优点，是一种有广泛应用前景的新型陶瓷材料。本文介绍了ＴｉＢ_２材料的制备、烧结及其复相陶瓷的研究现状，对其力学性能、抗氧化性能和摩擦学性能进行了评价。     

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。     

SiC/莫来石复相多孔陶瓷气孔率和强度的影响因素

以煅烧高岭土、Al(OH)3粉末、SiC粉末为主要原料,以石墨为造孔剂制备了SiC/莫来石复相多孔陶瓷,研究了造孔剂含量、碳化硅颗粒粒径以及烧结温度对SiC/莫来石复相多孔陶瓷抗弯强度和气孔率的影响,并分别用XRD和SEM分析晶相组成和断面显微结构.结果表明:当SiC粒径为60 μm,造孔剂含量为15％时,在1400℃下保温3h制备的样品综合性能最佳,其孔隙率为30.3％,抗折强度达到58.0 MPa.