氮化硼对锆刚玉莫来石材料力学性能及显微结构的影响

研究了锆刚玉米莫来石－氮化硼复合材料的显微结构及力学性能，结果表明，在锆刚玉莫来基质引入氮化硼，降低材料的抗折强度，但可提高断裂韧性。这是氮化硼的微裂纹增韧作用所致。氮化硼的编织状结构可阻碍晶界的滑移，降低材料高温强度的衰减率。材料内生成的针状９Ａｌ２Ｏ３．２Ｂ２Ｏ３，在断裂过程生产拔出效应，有利于力学性能的提高。     

锆刚玉莫来石—氮化硼复合材料的抗氧化性能研究

推导了锆刚玉莫来石－氮化硼复合材料１０００－１２００℃温度范围内的氧化动力学模型，并用实验数据予以验证。     

锆刚玉莫来石-碳化硅复合材料的显微结构

采用OM、SEM、TEM及EDAX等手段研究了锆刚玉莫来石-碳化硅复合材料的显微结构。结果表明,ZrO_2及SiC均匀地分散于刚玉/莫来石构成的基质中。刚玉-刚玉(或莫来石)及莫来石-莫来石的晶间表面多数存在非晶质薄膜,但也有刚玉-莫来石两相直接结合的相界因扩散而形成固溶层。ZrO_2-刚玉(或莫来石)及SiC-刚玉(或莫来石)的相表面因相间扩散形成固溶层或扩散层而皆属直接结合。在刚玉和莫来石晶体里观察到有晶内ZrO_2存在,其形成原因可能是在烧结过程中,刚玉或莫来石晶体再结晶长大而包裹ZrO_2微粒所致。     

锆刚玉莫来石—氮化硼系复合材料抗热震性的研究

对以锆刚玉莫来石为基引入１０％－３０％ＢＮ和以ＢＮ为基引入１０％－３０％锆刚玉莫来石的两类试样进行了抗热震性的研究。结果表明；在氧化物基料中引入ＢＮ，可以明显提高材料的抗热震性，认为这主要是ＢＮ的热膨胀系数的各向异性而引起的大量微裂纹所致。     

锆刚玉莫来石－氮化硼系复合材料抗热震性的研究

对以锆刚玉莫来石为基引入１０％～３０％（以质量计，下同）ＢＮ和以ＢＮ为基引入１０％～３０％锆刚玉莫来石的两类试样进行了抗热震性的研究。结果表明：在氧化物基料中引入ＢＮ，可以明显提高材料的抗热震性，认为这主要是ＢＮ的热膨胀系数的各向异性而引起的大量微裂纹所致。在ＢＮ基料中引入不超过２０％锆刚玉莫来石时，材料仍保持其优良的抗热震性。ＢＮ的编织状结构可以缓冲热震应力，阻碍热震裂纹的扩展。     

ZrB_2－刚玉莫来石质复合材料显微结构及力学性能的研究

通过对不同刚玉－莫来石含量的ＺｒＢ２材料力学性能及显微结构的研究，探讨了刚玉莫来石对ＺｒＢ２强度和韧性的影响，同时也分析了强化和韧化机制。     

SrO对刚玉锆莫来石材料的性能与结构影响研究

对氧化锶的加入量对刚玉锆莫来石材料的性能与结构的影响进行了分析，认为不超过3％的氧化锶对于稳定氧化锆的结构，改善性能有利。而氧化锆的作用，是以其共晶体的溶解改善基质的组成与侵蚀后渣的成分，以提高粘度来降低渣的渗透侵蚀。     

锆莫来石耐火材料的显微结构研究

用ＸＲＦ，ＯＭ，Ｓｔｅｒｅｏｌｏｇｙ等方法来锆莫来石耐火材料试样进行了剖析研究，测试了一系列数据，说明了锆莫来石耐火材料的显策结构和所具有的良好性能因果关系及其结构－性能之间存在的必然联系。     

烧结刚玉锆莫来石材料的铝硅锆共析结构研究

通过对烧结刚王锆莫来石复合材料的高温缓冷试样及高温水淬冷试样的电子探针及能谱分析,发现其微观结构中存在纤维状、骨架状、线状、针柱状、细棒状等有定向规律分布的铝硅锆共析结构存在,其组成为ＺｒＯ２－ＳｉＯ２－Ａｌ２Ｏ３成份。     

烧结刚玉锆莫来石材料的铝硅锆共析结构研究

通过对烧结刚玉锆莫来石复合材料的高温缓冷试样及高温水淬冷试样的电子探针及能谱分析,发现其微观结构中存在纤维状、骨架状、线状、针柱太、细棒状等有定向规律分布的名硅锆共析结构慧其组成为ＺｒＯ２－ＳｉＯ２－Ａｌ２Ｏ３成份。     

Effect of boron nitride nanosheets addition on the mechanical and dielectric properties of magnesium oxide ceramics

Boron nitride nanosheets (BNNSs)/magnesium oxide (MgO) composites were prepared via hot pressing. Mechanical properties of MgO ceramics were improved obviously in virtue of adding BNNSs. The bending strength of the 1 wt% BNNSs/MgO composite increased by about 85% than that of the monolithic MgO. The fracture toughness increased by 34% with the addition of 1.5 wt% BNNSs. Microstructural analyzes have shown that the toughening mechanisms are combinations of the pull-out and bridging of BNNSs, crack deflection, and crack bypassing mechanisms. The addition of a small amount of BNNSs don't destroy the excellent dielectric properties of composites. The dielectric constant of the sample doped with 1 wt% BNNSs was about 9.5 in the whole X-band and the vast majority of P-band, and the loss tangent was less than 5 × 10⁻³ in 10–15.8 GHz.     

Effect of boron addition on microstructure,mechanical properties and oxidation resistance of TaC ceramics

TaC ceramics with 0.03–0.60?wt% of boron additions were prepared by hot pressing at 2100?°C for 1?h under a pressure of 40?MPa. Effects of boron content on densification, phase composition, microstructure, mechanical properties and oxidation resistance of the TaC ceramics were investigated. When the boron content was 0.12?wt% and above, full density was obtained due to reactions between boron and oxygen impurity at presence of TaC. Minor phases of TaB₂ and C were formed in the 0.24 and 0.60?wt% B compositions after gas-out of the oxygen impurity. Microstructure of the TaC ceramics was refined with increasing in boron content. The TaC ceramic with 0.24?wt% of boron showed the best mechanical properties with a Vickers hardness, flexural strength and fracture toughness of 17.7?GPa, 534?MPa and 4.6?MPa?m^1/2, respectively. When more boron was added, interfacial bonding of the TaC grains was strengthened causing a decrease in fracture toughness. Oxidation resistance of the TaC ceramics increased with boron content. Particularly, the 0.60?wt% B composition showed a weight gain of 0.0018?g/cm² after oxidization at 800?°C in air for 3?h.     

Effect of hBN addition on the fabrication,mechanical and tribological properties of Sialon materials

This work aims to investigate the effect of hBN on the friction and wear resistance of Sialon composite. Sialon and its composite with 10 wt% hBN were fabricated by SPS sintering. The effect of hBN additive on the phase composition, microstructure, densification behavior, mechanical and dry sliding tribological properties of Sialon material was studied. Being sintered at 1600 °C for 10 min, compared to monolithic Sialon, Sialon-hBN composite has more refined β-Sialon grains with smaller aspect ratios and slightly declined relative density. The hardness of the Sialon-hBN composite was reduced due to the weak bonding between Sialon and hBN grains. Nevertheless, its fracture toughness increased ascribing to the toughening mechanisms, including crack deflection and crack bridging. hBN had an essential impact on the tribological performances of the composite due to its lower friction coefficient and good lubrication action. Under the same densification level (i.e., with a relative density of around 97.5%), the friction and wear resistance of Sialon-hBN composite were much better than monolithic Sialon. The main wear mechanisms were tribolayer formation, oxidized wear, and abrasive wear.     

Processing,microstructure, and mechanical properties of zirconium diboride-boron carbide ceramics

The processing, microstructure, and mechanical properties of zirconium diboride-boron carbide (ZrB₂-B₄C) ceramics were characterized. Ceramics containing nominally 5, 10, 20, 30, and 40 vol% B₄C were hot-pressed to full density at 1900 °C. The ZrB₂ grain size decreased from 4 to 2 µm and B₄C inclusion size increased from 3 to 5 µm for B₄C additions of 5 and 40 vol% B₄C, respectively. Elastic modulus decreased from 525 to 515 GPa and Vickers hardness increased from 15 to 21 GPa as the B₄C content increased from 5 to 40 vol%, respectively, following trends predicted using linear rules of mixtures. Flexure strength and fracture toughness both increased with increasing B₄C content. Fracture toughness increased from 4.1 MPa m^½ at 5 vol% B₄C to 5.3 MPa m^½ at 40 vol% B₄C additions. Flexure strength was 450 MPa with a 5 vol% B₄C addition, increasing to 590 MPa for a 40 vol% addition. The critical flaw size was calculated to be ~30 µm for all compositions, and analysis of the fracture surfaces indicated that strength was controlled by edge flaws generated by machining induced sub-surface damage. Increasing amounts of B₄C added to ZrB₂ led to increasing hardness due to the higher hardness of B₄C compared to ZrB₂ and increased crack deflection. Additions of B₄C also lead to increases in fracture toughness due to increased crack deflection and intergranular fracture.     

Effect of Y-TZP addition on the microstructure and properties of titania-based composites

To maintain the bioactivity and to improve the mechanical properties of titania, both pure titania ceramics and titania–yttria-stabilized tetragonal zirconia (Y-TZP) composites with 5, 10, and 15 vol.%Y-TZP were prepared via a sol–gel precipitation method. A titania precursor (titanium butoxide) was mixed with a submicron-sized Y-TZP powder, followed by hydrolysis-condensation reactions, green compact forming, and sintering in air at 1200–1350 °C. It was found that the addition of Y-TZP resulted in reduced rutile titania grain size from 13 to 3 μm. The Y-TZP tetragonal phase also resulted in improved mechanical properties of the titania–Y-TZP composites. For instance, the titania–15 vol.%Y-TZP composite had a hardness value of 983 kg/mm², a bending strength of 160 MPa, and a fracture toughness of 3.79 MPa m^0.5. While the addition of Y-TZP increased the mechanical properties, it also decreased the bioactivity of the composites.     

Influence of sintering atmosphere and BN additives on microstructure and properties of porous SiC ceramics

The effects of the boron nitride (BN) content on the electrical, thermal, and mechanical properties of porous SiC ceramics were investigated in N₂ and Ar atmospheres. The electrical resistivity was predominantly controlled by the sintering atmosphere and secondarily by the BN concentration, whereas the thermal conductivity and flexural strength were more susceptible to changes in the porosity and necking area between the SiC grains. The electrical resistivities of argon-sintered porous SiC ceramics (6.3 × 10⁵ – 1.6 × 10⁶ Ω·cm) were seven orders of magnitude higher than those of nitrogen-sintered porous SiC ceramics (1.5 × 10⁻¹ – 6.0 × 10⁻¹ Ω·cm). The thermal conductivity and flexural strength of the argon-sintered porous SiC ceramics increased from 8.4–11.6 W·m⁻¹ K⁻¹ and from 9.3–28.2 MPa, respectively, with an increase in the BN content from 0 to 1.5 vol%, which was attributed to the increase in necking area and the decrease in porosity.     

Effect of diopside addition on sintering and mechanical properties of alumina

In this paper, diopside was introduced in alumina as a sintering aid and fine structural alumina matrix ceramic materials were fabricated by pressureless sintering. The relative density, hardness, fracture toughness and bending strength of the new fabricated composites were measured. Tribological tests were carried out at a given rotation speed of 160 rpm and in a normal load ranged from 50 to 200 N. The experiment results show that the introduction of diopside can enhance densification rate, which may contribute to the improvement in mechanical properties and result in enhanced wear resistances. The effects of diopside on mechanical properties and microstructures of fine structural alumina matrix ceramic materials were analyzed and discussed.     

Effect of c-BN surface modification on the microstructure and mechanical properties of (Ti,W)C-based cermet tool materials

Alumina-coated cubic boron nitride (c-BN) particles (c-BN@Al₂O₃) were prepared using a heterogeneous nucleation method. Then, they were added to a (Ti,W)C-based cermet tool material after synthesis via vacuum hot-press sintering. The microstructure and mechanical properties of the (Ti,W)C-based cermet tool material with varying c-BN@Al₂O₃ contents were recorded and analyzed. The results show that with increasing c-BN@Al2O3 concentration, the relative density, flexural strength, fracture toughness, and Vickers hardness all increase first and then decrease, and the average grain size first decreases and then increases. The introduction of Al₂O₃ into the c-BN particles used for surface modification can improve the wettability and interfacial bonding strength between the c-BN and matrix particles, restrain the grain growth of the matrix particles, and improve the flexural strength of cermet tool materials. The addition of c-BN@Al₂O₃ also alters the crack propagation mechanism of the cermet tool material and introduces multiple toughening mechanisms to improve the fracture toughness of the cermet tool material. The high hardness of c-BN and Al₂O₃ is the main reason for the increase in hardness; however, excessive addition of such material reduces the relative density, resulting in a decrease in hardness.     

Influence of hexagonal boron nitride nanosheets on phase transformation,microstructure evolution and mechanical properties of Si3N4 ceramics

Fully dense Si₃N₄ materials with 1 wt.% (～ 1.5 vol.%) and 2 wt.% (～ 3.0 vol.%) h-BN nanosheets were prepared by spark plasma sintering at 1750 °C with the dwell of 7 min under a pressure of 50 MPa in a vacuum. BN nanosheets with different dimensions were prepared by ultrasound-assisted liquid phase exfoliation of h-BN powder, followed by centrifugation at different speeds (1000 rpm and 3000 rpm). The addition of BN nanosheets hindered the particle rearrangement stage of sintering, which resulted in the delayed α→β phase transformation of Si₃N₄. To study a direct effect of BN nanosheets on the mechanical properties of Si₃N₄, the results were compared to the monolithic Si₃N₄ with similar grain size and α/β-Si₃N₄ ratio. The addition of 2 wt.% h-BN nanosheets (1000 rpm) increased both the fracture toughness (～ 26 %) and the strength (～ 45 %) of Si₃N₄, when compared to the monolithic Si₃N₄ with similar microstructure.     

Influence of carbon nanotubes as secondary phase addition on the mechanical properties and amorphization of boron carbide

The mechanical properties and amorphization response of a carbon nanotube (5 wt.%) boron carbide (CNT-B₄C) composite with 1 μm grain size are investigated, and compared to those of coarse-grained (10 μm grain size) and ultrafine-grained (0.3 μm grain size) monolithic boron carbides. The quasi-static and dynamic uniaxial compressive strengths for CNT-B₄C were statistically the same as those of the ultrafine-grained ceramic and higher than the coarse-grained material, contradicting the expected grain size hierarchy (Hall-Petch-type relationship). Addition of CNTs to B₄C resulted in decreased quasi-static hardness compared to the large grain size material; however, dynamic hardness was substantially improved compared to quasi-static values. CNT pullout and crack bridging were observed to be possible toughening mechanisms. Finally, Raman spectroscopy was used to quantify amorphization, and it was concluded that addition of CNTs to boron carbide does not alter the propensity for amorphization, but does improve mechanical properties by enhanced toughening.