Corrosion resistance of AlN–SiC–TiB2 composite in air

The oxidation kinetics of AlN–SiC–TiB₂ composite in air has been investigated in terms of a theoretical analysis associated with the experiment data. The effects of temperature and temperature heating rate on the oxidation reaction have been discussed by using the “characteristic oxidation time”. The results show that the calculated results by our model can give a good agreement with the experimental data. From this study it is shown that, the “characteristic oxidation time” is a very useful parameter for comparing the property of oxidation resistance for different composites.     

Preparation of the TiB2 coatings by electroplating in molten salts

The improvement of titanium diboride (TiB₂) coatings over the molybdenum substrate was investigated by comparing the electrochemical techniques of continuous current plating (CCP) and periodically interrupted current (PIC). The solvent used was a eutectic Flinak mixture (LiF-NaF-KF, 46.5:11.5:42 molar ratio) with solutes K₂TiF₆ and KBF₄ with the electrochemically-active components in the molar ratio of one to five. The coatings produced by PIC show improvements in morphology and microstructure for the suitable conditions: i = 0.5 A/cm², frequency = 100 Hz, the time ratio t_c/t_off (current on/current off) = 4/1. X-ray diffraction (XRD) analyses indicated that the coatings are composed of the relatively pure TiB₂ and the preferred orientation is [001] + [110], which is in accordance with the prediction of the two-dimensional crystal nuclei theory.     

不同TiB2颗粒粒径的TiB2/Cu复合材料耐电弧侵蚀行为

采用放电等离子烧结法（SPS）制备了不同TiB₂颗粒粒径的3wt% TiB₂/Cu复合材料,研究了3wt% TiB₂/Cu复合材料致密度、导电率、硬度和耐电弧侵蚀性能随TiB₂颗粒粒径的变化规律,重点分析了不同TiB₂颗粒粒径的3wt% TiB₂/Cu复合材料耐电弧侵蚀行为。结果表明:3wt% TiB₂/Cu复合材料致密度和硬度随TiB₂颗粒粒径的增大而略有降低;TiB₂颗粒粒径越小,TiB₂/Cu复合材料的综合性能越好。随着TiB₂颗粒粒径的增大,3wt% TiB₂/Cu复合材料耐蚀稳定性降低,3wt% TiB₂/Cu阴极材料的损耗量明显增加;当TiB₂颗粒粒径为10 μm时,3wt% TiB₂/Cu复合材料的耐电弧侵蚀性能最佳。电弧蚀形貌观察表明:不同TiB₂颗粒粒径的3wt% TiB₂/Cu复合材料经电弧侵蚀后,3wt% TiB₂/Cu复合材料均由阴极向阳极发生转移;随着TiB₂颗粒粒径的增大,阴极质量损耗逐渐增加,触头表面电弧侵蚀面积增加;而在Cu基体中引入较小的TiB₂颗粒,有利于减弱电接触实验过程中TiB₂/Cu复合材料的喷溅现象。      

Mechanical properties of superhard TiB2 coatings prepared by DC magnetron sputtering

Superhard titanium diboride (TiB₂) coatings (H_v> 40 GPa) were deposited in Ar atmosphere from stoichiometric TiB₂ target using an unbalanced direct current (d. c.) magnetron. Polished Si (0 0 1), stainless steel, high-speed steel (HSS) and tungsten carbide (WC) substrates were used for deposition. The influence of negative substrate bias, U_s, and substrate temperature, T_s, on mechanical properties of TiB₂ coatings was studied. X-ray diffraction (XRD) analysis showed hexagonal TiB₂ structure with (0 0 01) preferred orientation. The texture of TiB₂ coatings was dependent upon the ion bombardment (U_s increased from 0 to −300 V) and the substrate heating (T_s increased from room temperature (RT) to 700 °C). All TiB₂ coatings were measured using microhardness tester Fischerscope H100 equipped with Vickers and Berkovich diamond indenters and exhibited high values of hardness H_v up to 34 GPa, effective Young's modulus E*=E/(1-ν) ranging from 450 to 600 GPa; here E and ν are the Young's modulus and Poisson's ratio, respectively, and elastic recovery W_e≈80%. TiB₂ coating with a maximum hardness H_v≈73 GPa and E*≈580 GPa was sputtered at U_s=−200 V and T_s=RT. Macrostresses of coatings σ were measured by an optical wafer curvature technique and evaluated by Stoney equation. All TiB₂ coatings exhibited compressive macrostresses.     

Microstructure and mechanical properties of as-deposited and annealed TiB2/BN superlattice coatings

TiB₂/BN multilayers with the modulation ratios (t_TiB2:t_BN) ranging from 1:1 to 16:1 and a constant modulation period of 24 nm were prepared by magnetron sputtering. The TiB₂/BN multilayers were subsequently annealed in a vacuum environment at temperatures of 500-700 °C for 30 min, then characterized by extensive measurements. All multilayers exhibited small grain sizes and stable layer structures with polycrystalline with TiB₂(001), TiB₂(101), TiB₂(002) textures or amorphous BN, resulting in higher hardness and elastic modulus than that of individual monolithic TiB₂ or BN coatings. The hardness of as-deposited multilayer can reach as high as 39.34 GPa at t_TiB2:t_BN = 13:1, meanwhile the friction coefficient got to 0.028, which was also the lowest. The hardness and friction were almost unchanged after annealing at 500-700 °C, which was attributed to good thermal stability in the layer structure and the existence of stable TiB_xN_y phases.     

Synthesis of in situ Al–TiB2 composites using stir cast route

When elemental Ti and B powders were added to molten Al at above 1000°C, fine in situ TiB₂ particulates were formed through Al–Ti–B exothermic reaction. By optimising the nucleation of TiB₂, the tensile and yield strengths of a synthesised Al–15V_f%TiB_s composite were twice that of matrix material. Modification of Al-matrix with 4.5 wt%Cu tripled the tensile and yield strengths at peak-aged condition. Owing to the co-presence of brittle Al₃Ti flakes with TiB₂ particles in the composites synthesised by the Al–Ti–B system, ductility was reduced to 68% and 84% in composites with Al- and Al–Cu matrices, respectively. When the (Ti + B) mixture was incorporated with 3 wt%C, TiB₂ and TiC reinforcing phases were simultaneously produced in the composite with Al–Cu matrix. Such an approach reduced Al₃Ti compound in the composite considerably. Although the presence of Cu in the composite was found to promote the formation of Al₃Ti, its effect on the fluidity caused the melt recovery to increase from 33% to 52%.     

Mechanochemical synthesis and characterization of TiB2 and VB2 nanopowders

A novel method for the synthesis of transition-metal boride nanopowder has been developed using a mechanochemical reaction between LiBH₄, LiH and transition-metal chloride (TiCl₃ and VCl₃) by high energy ball milling. This method successfully produces TiB₂ and VB₂ particles dispersed within a soluble LiCl matrix. Subsequent washing with distilled water, ethanol and acetone to remove the LiCl matrix phase yields TiB₂ and VB₂ nanopowders of 15-60 nm particle size. From the X-ray diffraction patterns and high resolution transmission electron microscopy image, it is found that each particle is polycrystalline consisting of 3-5 nm crystallites. Neither particle nor crystallite size are increased significantly after heating at 680 °C.     

Influence of modulation ratio on the structure and mechanical properties of TiB2/TiAlN multilayered coatings

TiB₂/TiAlN multilayered coatings with various modulation ratios (t_TiB2:t_TiAlN) were grown using radio-frequency magnetron sputtering at room temperature. Nanoindentation, tester for material surface properties, and XRD were used to investigate the influence of modulation ratio on microstructure and properties of the multilayers. All multilayers showed improved mechanical properties, compared with the average value of the monolithic TiB₂ and TiAlN coatings. The multilayer with modulation ratio of 5:2 displayed the highest hardness (36 GPa) and longest time to crack during wear. A marked layer structure with the strong mixture of TiAlN (111), AlN (111), and TiB₂ (001) textures with smaller grain sizes was responsible for the enhanced hardness.     

Sol–gel synthesis and characterization of Li2O–As2O5–SiO2 glassy system

The ternary 10% Li₂O + 90% (xAs₂O₅ + (1 − x) SiO₂) (x = 0.025, 0.05, 0.075 and 0.1) (LAS) glassy system with different compositions were prepared using sol–gel technique. All the prepared samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry techniques. The observed peak-free XRD patterns confirm the amorphous phase of the prepared LAS compounds. Structural coordination of LAS glassy samples was confirmed by Fourier transform infrared spectroscopy. Thermal behavior of the glassy samples was characterized by differential scanning calorimetry. Bulk conductivity of all the LAS glassy samples was calculated by analyzing the impedance data measured at different temperatures. Activation energy (E_a) is evaluated from the log σT vs. 1000/T plot and it is found to be 0.837 eV.     

TiB2 and TiC stainless steel matrix composites

Stainless steel matrix composites reinforced with TiB₂ or TiC particulates have been in situ produced through the reactive sintering of Ti, C and FeB. X-ray diffraction analysis confirmed the completion of reaction. The TiB₂, TiC and steel were detected by X-ray diffraction analysis. No other reaction product or boride was found, indicating the stability of TiB₂ and TiC in steel matrix. The SEM micrographs revealed the morphology and distribution of in situ synthesized TiB₂ and TiC reinforcements in steel matrix. During sintering the reinforcements TiB₂ and TiC grew in different shapes. TiB₂ grew in hexagonal prismatic and rectangular shape and TiC in spherical shape.     

TiB2/Cu复合材料的电弧侵蚀行为

采用放电等离子烧结法（SPS）制备TiB₂质量分数为1wt%~5wt%的TiB₂/Cu复合材料,测试其导电率和硬度。当TiB₂质量分数由0增至5wt%时,复合材料的导电率由96.9%（International Annealed Copper Standard,IACS）降至65.1%（IACS）,布氏硬度由42.8增至65.2。对所制备的不同TiB₂质量分数的TiB₂/Cu复合材料在直流24 V、不同电流条件下进行电接触实验,探究TiB₂添加量和电流对TiB₂/Cu复合材料耐电弧侵蚀性能的影响。结果表明,TiB₂/Cu复合材料的平均燃弧时间、平均燃弧能量和材料损耗量随着电流的增加而增加,TiB₂/Cu复合材料的阴极损耗量高于阳极,整体上TiB₂/Cu复合材料由阴极向阳极转移。在24 V和25 A条件下,不同TiB₂质量分数的TiB₂/Cu复合材料的燃弧时间和燃弧能量随操作次数增加不断波动,整体上呈逐渐增加的趋势,3wt% TiB₂/Cu复合材料的稳定性最高,平均燃弧时间和燃弧能量最低。随着TiB₂质量分数的增加,TiB₂/Cu复合材料损耗量降低,表面蚀坑变浅。     

Sensitivity enhancement for H2 gas detection using a SnO2–Ag2O–PdOx nanocrystalline system

Thick film H₂ sensors were fabricated using SnO₂ loaded with Ag₂O and PdO_x. The composition that gave highest sensitivity for H₂ was in the wt.% ratio of SnO₂:Ag₂O:PdO_x as 93:5:2. The nano-crystalline powders of SnO₂–Ag₂O–PdO_x composites synthesized by sol–gel method were screen printed on alumina substrates. Fabricated sensors were tested against gases like H₂, CH₄, C₃H₈, C₂H₅OH and SO₂. The composite material was found sensitive against H₂ at the working temperature 125 °C, with minor interference of other gases. H₂ gas as low as 100 ppm can be detected by the present fabricated sensors. It was found that the sensors based on SnO₂–Ag₂O–PdO_x nanocrystalline system exhibited high performance, high selectivity and very short response time to H₂ at ppm level. These characteristics make the sensor to be a promising candidate for detecting low concentrations of H₂.     

Several shape-controlled TiO2/TiB2 hybrid materials with a combined growth mechanism

Several kinds of TiO₂/TiB₂ hybrid materials with different morphologies, including hollow bipyramid structure with truncations, pineapple structure, urchin structure and nanowall structure, have been successfully synthesized by a facile solvothermal approach in the aqueous solution of ethylenediamine. The effect of ethylene ediamine on the shape change of the final products was investigated in detail. With the increase of ethylenediamine, anatase TiO₂ on the TiB₂ core is gradually evolved from nanoparticles, nanorods to nanosheets. Based on attachment theory, Oswald ripening phenomenon, chelating effect and Kirkendall effect, a possible formation mechanism for such TiO₂/TiB₂ hybrid materials was proposed to explain the morphology evolution.     

Electrical properties of glasses in the Na2O–MoO3–P2O5 system

A range of coloured electronic or mixed ionic–electronic glasses has been evidenced in the Na₂O–MoO₃–P₂O₅ system. The properties of these glasses have been studied along different composition lines corresponding either to a fixed Na₂O content or a constant Mo/P ratio. An EPR spectroscopy investigation of these glasses has allowed to determine the Mo⁵⁺ ion percentages in these materials. The electrical properties of these glasses have been studied by impedance spectroscopy, and the electronic and ionic contributions have been evaluated. The properties of these sodium glasses have been compared with those of lithium glasses with the same compositions.     

多粒径TiB2/Cu复合材料耐电弧侵蚀行为

采用粉末冶金工艺制备了不同配比的多粒径(2 μm+10 μm+50 μm) TiB₂/Cu复合材料。通过JF04C触点材料测试系统对多粒径TiB₂/Cu复合材料进行耐电弧侵蚀性能试验,研究(2 μm+10 μm+50 μm) TiB₂颗粒质量比分别为1∶1∶1、1∶1∶3、1∶3∶1、3∶1∶1时,TiB₂/Cu复合材料的耐电弧侵蚀性能及电弧侵蚀形貌变化规律,探究多粒径配比对TiB₂/Cu复合材料表层耐电弧侵蚀行为的影响。结果表明:当(2 μm+10 μm+50 μm) TiB₂颗粒质量比为1∶1∶1时,TiB₂/Cu复合材料相对密度和导电率最高,分别为99.1%和87.1%IACS。当(2 μm+10 μm+50 μm) TiB₂颗粒质量比为1∶1∶1和1∶3∶1时,TiB₂/Cu复合材料的组织均匀性较好,电弧侵蚀后材料损失相同,材料转移量最少。其中,质量比为1∶3∶1时,TiB₂/Cu复合材料平均燃弧能量最低,且燃弧时间和燃弧能量最稳定。研究表明,这与复合材料的综合物理性能密切相关。在颗粒增强Cu基复合材料设计过程中,引入合适配比的多粒径TiB₂颗粒有助于提高TiB₂/Cu复合材料的密度、导电率等综合物理性能。电弧侵蚀过程中,不同粒径的TiB₂颗粒相互协同作用,有助于提高TiB₂/Cu复合材料的耐电弧侵蚀性能和服役稳定性。      

TiB2陶瓷与Mo金属的燃烧反应焊接

采用燃烧反应工艺焊接了TiB₂陶瓷与金属Mo,对中间反应层生成物进行了XRD物相分析,对焊接界面结合情况进行了电子探针分析。温度和中间层组分对焊接件的抗弯强度和抗剪切强度有一定的影响。分析表明:抗弯强度在焊接温度为1500℃,中间层Mo含量为80wt%时达最大值;在焊接温度为1500℃,中间层组分中含Mo为40wt%时所得焊接件抗剪切强度值达最大。     

TiB2与BN复相陶瓷的渗流模型

试验结果证实,TiB₂与BN复相陶瓷的导电性能符合渗流理论,原料粉粒度配比下,其渗流阀值为V_c%=22.9%;原料粉粒度比的改变将改变渗流阀值,从而改变各配比下的电阻率值;TiB₂与BN在SPS系统中快速烧结,晶粒的尺度比与原料粉的粒度比基本保持一致。     

Low-temperature ionic conductivity of the solid solution in the system ZrO2–Y2O3–Yb2O3

Compositional dependence of ionic conductivity in the system ZrO₂–Y₂O₃–Yb₂O₃ was investigated in the temperature range 573–873 K using the complex impedance technique. It was shown that the conductivity decreases with increasing concentration of Yb₂O₃ in the system ZrO₂–Y₂O₃–Yb₂O₃. Analyzing the experimental data according to the classic Arrhenius equation showed that such an experimental phenomenon can be attributed to the tighter association between Yb³⁺ and oxygen vacancy, compared with that between Y³⁺ and oxygen vacancy, which hinders the migration of oxygen vacancy in the materials.     

Cu-Zr合金基体中TiB2的原位反应合成

本文作者利用原位反应合成法制备了TiB₂/Cu-Zr复合材料,并对其显微结构进行了观察。分析了合成TiB₂的反应过程。结果表明:TiB₂在Cu-Zr基体中以两种形态存在,分布均匀,尺寸为0.5 μm~10 μm;在建立TiB₂反应合成机制模型的基础上,简单描述了不同形态TiB₂的生长机制。