Meihua Hu,Ning Bi,Mingming Liu,Guangjin Gao,Shangsheng Li,Taichao Su
The improved TiB2 ceramics were obtained in sintering process at the pressure of 5.5 GPa and temperature of 1550 °C in presence of metallic Co powder. The effect of Co content (ranging from 0 wt.% to 10.0 wt.%) on the phase composition, density, microstructure, Vickers hardness and thermal conductivity of TiB2 ceramics was analyzed. A small amount of new phase Co2B has been created in the reaction of TiB2 and Co. The relative density of sintered TiB2 ceramics reached 98.1 %. When the mass fraction of Co increased, the porosity increased, while the hardness first increased and then decreased. The maximal Vickers hardness values were equal to 33.3 GPa or 28.2 GPa when the used load was of 4.9 N or 9.8 N, respectively. The highest reached value of thermal conductivity was 88.9 W˙m−1 ˙ K−1. The dense TiB2 ceramics with improved hardness and thermal conductivity were ascribed to the high pressure sintering method and Co sintering aid. High pressure sintering method provides a new way for the preparation of ceramics materials.
In the present work, the powder mixtures of TiB 2 containing 2.0mol.% carbon black with trace La 2 O 3 and Al 2 O 3 are used to fabricate textured TiB 2 ceramic using hot–pressing at 1800 °C, and then the TiB 2 ceramic is hot–forged. The results of microstructural observation indicated that the addition of the powder mixtures of Al 2 O 3 and La 2 O 3 was favorable to the rearrangement of the anisotropic TiB 2 grains, whereas was unfavorable to the improvement of the relative density during hot–pressing and hot–forging. The flexural strength and the fracture toughness of textured TiB 2 ceramic fabricated using the combination of oxides and hot–forging were improved significantly, whereas hardness did not show obvious change. The results here pointed to a novel method for fabricating textured TiB 2 –based ceramics.
Da-Wang Tan,Zhen-Yong Lao,Zhan Zhang,Wei-Ming Guo,Shi-Kuan Sun,Hua-Tay Lin
B 4 C-TiB 2 ceramics (TiB 2 ranging 5~70 vol%) with Mo-Co-WC as the sintering additive were prepared by spark plasma sintering. In comparison with B 4 C-TiB 2 without additive, the enhanced densification was evident in the sintered specimen with Mo-Co-WC additive. Core-rim structured grain was observed around TiB 2 grains. The interface of the rim between TiB 2 and B 4 C phases demonstrated different feature: the inner borderline of the rim exhibited a smooth feature, whereas a sharp curved grain boundary was observed between the rim and the B 4 C grain. The formation mechanism is discussed: the epitaxial growth of (Ti,Mo,W)B 2 rim around the TiB 2 core may occur as a result of the solid solution and dissolution-precipitation between TiB 2 phase and the sintering additive. It was revealed that the fracture toughness increased as the content of TiB 2 content increased, alongside the decreased hardness. B 4 C-30 vol% TiB 2 specimen demonstrated the optimal combination of mechanical properties, reaching Vickers hardness of 24.3 GPa and fracture toughness of 3.33 MPa·m 1/2 .
Yafei Pan,Lei Huang,Jiuxing Zhang,Yong Du,Fenghua Luo
BxC-TiB2 ceramic composites were fabricated via reactive spark plasma sintering using TiC and B as the raw materials. The impact of B/TiC mole ratios on the phase compositions, densification behaviors, microstructure, and mechanical properties of the ceramic composites were investigated. The results showed that the stoichiometry of ‘BxC’ could be tailored by changing initial boron content and the obtained B4.5C, B6.5C and B8.5C phases have the same crystal structure (R-3 m). The excess of B enhanced the reaction between TiC and B, which released a large amount of hot energy and promoted the densification of the composites. The TB8.5 composite sintered at 1900°C had the best comprehensive mechanical properties, with hardness and flexural strength of 40.36 GPa and 551 MPa, respectively. The formation of nano-sized TiB2 grains induced by reaction were beneficial for improving the mechanical properties of these composites.
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