共查询到20条相似文献,搜索用时 10 毫秒
1.
A ZrB2 ceramic containing 20 vol.% SiC and 10 vol.% graphite flake (ZrB2-SiC-G) was fabricated by hot pressing. It was shown that the fracture toughness was improved due to the introduction of graphite flake, whereas the flexure strength and hardness decreased slightly. The fracture toughness of ZrB2-SiC-G composite was 6.1 ± 0.3 MPa·m1/2, which was much higher than that of monolithic ZrB2, ZrB2-SiC composite and similar ZrB2-SiC-C composite. The toughening mechanisms are crack deflection and branching as well as stress relaxation near the crack tip. The results here pointed to a potential method for improving fracture toughness of ZrB2-based ceramics. 相似文献
2.
A ZrB2-based composite containing 20 vol.% nanosized SiC particles (ZSN) was fabricated at 1900 °C for 30 min under a uniaxed load of 30 MPa by hot-pressing. The microstructure and mechanical properties of the composite were investigated. It was shown that the grain growth of ZrB2 matrix was effectively suppressed by submicrosized SiC particles located along the grain boundaries. In addition, the mechanical properties of ZSN composite were strongly improved by incorporating the nanosized SiC particles into a ZrB2 matrix, especially for flexural strength (925 ± 28 MPa) and fracture toughness (6.4 ± 0.3 MPa•m1/2), which was much higher than that of monolithic ZrB2 and ZrB2-based composite with microsized SiC particles, respectively. The formation of intragranular nanostructures plays an important role in the strengthening and toughening of ZrB2 ceramic. 相似文献
3.
利用流延-叠层-热压烧结工艺制备层状ZrB_2-SiC/石墨(ZrB_2-SiC/G)陶瓷,研究了石墨弱界面层的方向性对其力学性能的影响;通过XRD、SEM等对层状ZrB_2-SiC/G陶瓷的物相、形貌进行观察分析。结果表明:层状ZrB_2-SiC/G陶瓷在平行方向上的弯曲强度为(382±25)MPa,略低于垂直方向的弯曲强度((429±30)MPa);平行方向的断裂韧性为(11.2±0.3)MPa·m~(1/2),比垂直方向的断裂韧性提高了75%。层状ZrB_2-SiC/G陶瓷在平行方向上的断裂韧性的提高主要是由于石墨弱界面层对裂纹的偏转、分叉和脱层作用。 相似文献
4.
Xueying Li Xinghong Zhang Jiecai Han Changqing Hong Wenbo Han 《Materials Letters》2008,62(17-18):2848-2850
A new oxidation method, high frequency induction heating, was introduced to investigate the rapid oxidation characteristics of ZrB2-SiC at 1800 °C up to 50 min. A high temperature was achieved within 30 s by adjusting the current or voltage. According to the isothermal test at 1800 °C, the oxidation kinetics for the composite followed a para-linear law. The specific weight gains increased from 4.86 to 12.89 mg/cm2 when the exposure time increased from 10 to 50 min. When exposure for 30 min, a thin outmost layer of SiO2, a ZrO2 layer and a thick SiC-depleted layer formed on the surface of specimens. The structural characteristic of oxidation layer obtained by high frequency induction heating was similar to those formed by standard oxidation furnace. 相似文献
5.
ZrB2基超高温陶瓷因其优异的高温抗氧化和烧蚀等性能,成为C/C复合材料理想的热防护涂层材料。本文从以下几个方面对C/C复合材料表面用ZrB2基超高温陶瓷涂层的研究现状进行了综述:介绍了ZrB2基超高温陶瓷涂层体系的主要制备技术,并对比了其制备的涂层抗氧化性和抗烧蚀性,总结了各制备方法的优点与不足;从单元、双元、三元材料掺杂改性的角度,详述了ZrB2基复合涂层常见的材料体系,总结了其改性思路;介绍了ZrB2基涂层在多层结构设计与开发方面的研究现状。最后简要展望了ZrB2基超高温陶瓷涂层未来的研究方向。 相似文献
6.
Weijie Li Xinghong Zhang Changqing Hong Jiecai Han Wenbo Han 《Materials Science and Engineering: A》2008,494(1-2):147
ZrB2–10 vol%SiC–20 vol%YSZ composites were prepared by hot-pressed sintering with yttria content ranging from 2 mol% to 8 mol% in YSZ. The phase constitution, microstructure and mechanical properties of the composites were found to be strongly dependent on the yttria content. The average grain size became bigger for the composites with higher yttria content. When the yttria content was below 3 mol%, there is no cubic zirconia in the polished surface of composites, and the flexural strength of the composites was above 740 MPa. With the increase in yttria content, the fracture toughness fell down from 6.4 MPa m1/2 to 5.6 MPa m1/2. Vickers’ hardness of the hot-pressed composites varied above 18 GPa without obvious effect of the yttria content. 相似文献
7.
为提高炭/炭(C/C)复合材料的高温抗氧化性能,同时分析涂层制备及高温氧化对涂层材料力学行为的影响,在C/C复合材料表面采用反应熔渗、料浆涂刷结合化学气相沉积工艺制备了SiC/ZrB2-SiC/SiC三层高温抗氧化涂层。利用SEM和XRD分析复合涂层的微观结构和相组成,考察涂层复合材料1500℃高温抗氧化和1500℃-室温的抗热震性能,研究高温氧化及热震对涂层C/C复合材料力学行为的影响。结果表明,复合涂层试样1500℃静态空气环境下具有优异的抗氧化及抗热震性能:1500℃氧化20 h后试样保持增重,1500℃至室温热震50次后增重为0.69%。因涂层制备过程中粉料的渗入反应,复合材料弯曲强度增长了7.08%。在经历1500℃氧化20 h和1500℃至室温50次热震后,涂层复合材料弯曲强度有所下降,且因材料界面结合力的减弱使得纤维拔出特征明显,材料塑性断裂特征增强。 相似文献
8.
Jianfeng Zhu Wenwen Yang Haibo Yang Fen Wang 《Materials Science and Engineering: A》2011,528(21):6642-6646
In situ composites of TiAl reinforced with Al2O3 particles are successfully synthesized from an elemental powder mixture of Ti, Al and Nb2O5 by the hot-press-assisted reaction synthesis (HPRS) method. The as-prepared composites are mainly composed of TiAl, Al2O3, NbAl3, as well as small amounts of the Ti3Al phase. The in situ formed fine Al2O3 particles tend to disperse on the matrix grain boundaries of TiAl resulting in an excellent combination of matrix grain refinement and uniform Al2O3 distribution in the composites. The Rockwell hardness and densities of TiAl based composites increase gradually with increasing Nb2O5 content, and the flexural strength and fracture toughness of the composites have the maximum values of 634 MPa and 9.78 MPa m1/2, respectively, when the Nb2O5 content reaches 6.62 wt.%. The strengthening mechanism was also discussed. 相似文献
9.
为探索第三组元Y2O3添加对Al2O3/ZrO2共晶陶瓷显微组织与机械性能的影响,本文利用低温度梯度的高温熔凝法制备了直径为20 mm的Al2O3/ZrO2(Y2O3)共晶陶瓷块体,采用SEM、EDS及XRD技术对共晶陶瓷进行微结构分析,并利用维氏压痕法对其硬度和断裂韧性进行测试。SEM结果表明,凝固组织由群集的共晶团结构组成,随着Y2O3添加量的增加,共晶团形态由胞状转变为枝晶状,内部相间距在1~2 μm范围内变化。力学测试表明,Y2O3摩尔分数小于1.1%时,由于组织内部存在低硬度m-ZrO2及微裂纹缺陷,故陶瓷硬度较低,约为(9.53±0.22 )GPa;当Y2O3摩尔分数为1.1%时,陶瓷硬度最大,约为(18.05±0.27)GPa;当Y2O3的摩尔分数大于1.1%时,由于共晶团边界区内气孔缺陷及粗大组织增多,引起陶瓷硬度值略有下降。低Y2O3摩尔分数添加时,陶瓷断裂韧性相对较高,约为(6.30±0.16)MPa·m1/2,这与其内部存在大量微裂纹缺陷有关;随着Y2O3添加量的增加,陶瓷的微裂纹数量减少、边界区内缺陷增多,断裂韧性降低。 相似文献
10.
Guobing YingXiaodong He Mingwei LiWenbo Han Fei HeShanyi Du 《Materials Science and Engineering: A》2011,528(6):2635-2640
High-purity and dense Cr2AlC has been successfully fabricated by hot-pressing, using Cr, Al and graphite as raw materials. Delamination, kink bands, monolamellar kink, transgranular crack and transgranular fracture of bulk Cr2AlC are found during the room-temperature test. The density, Vickers hardness, flexural strength, Young's modulus, compressive strength and fracture toughness of the Cr2AlC are 5.17 g/cm3, 4.9 GPa, 469 ± 27 MPa, 282 GPa, 949 ± 22 MPa and 6.22 ± 0.26 MPa m1/2, respectively. The strength of Cr2AlC could be greatly improved by second phase of Cr7C3. And the slipping of basal planes and slip system cold be hindered by Cr7C3, thus resulting in a lower toughness. 相似文献
11.
以B_4C、Zr、W为原料,采用反应热压烧结工艺制备了ZrB_2-ZrC-W_2Zr复合材料,系统研究了烧结温度对复合材料组织结构和力学性能的影响规律。结果表明,复合材料主要由ZrB_2、ZrC、W_2Zr和少量的W组成,随着烧结温度从1 600℃升高到1 900℃,W的含量略有增加,W_2Zr的含量略有减少,ZrB_2晶粒的形态由针状向板条状转变,晶粒尺寸逐渐增大,而长径比逐渐减小。复合材料的抗弯强度和断裂韧性随着烧结温度的升高先增大后减小,在1 850℃出现峰值,分别达到约560 MPa和5.5 MPa·m~(1/2)。 相似文献
12.
The present paper investigated the microstructure and mechanical properties of ZrB2-10 vol.%SiCp-10 vol.%ZrO2 composites hot pressed at three temperatures. Phase transformability from t-ZrO2 to m-ZrO2 during fracture was analyzed through calculating the volume fractions of m-ZrO2 and t-ZrO2 on polished and fracture surfaces. The densification temperature was found to have a significant effect on the microstructure, phase transformation and the properties of the composites. When the composite was hot pressed at 1950 °C, the average grain size was 9.5 µm, and the fracture toughness was 4.5 MPa·m1/2. Comparatively, when the composite was hot pressed at 1750 °C, the average grain size was 3.4 µm, and the fracture toughness increased by ~ 50% to 6.8 MPa·m1/2. 相似文献
13.
以ZrO_2、Mg、B_2O_3及Na_2B4O_7为原料,采用自蔓延高温合成技术制备ZrB2粉体。通过FactSage7.0软件计算,从热力学角度研究了该反应体系发生自蔓延反应的可能性。采用X射线粉末衍射物相分析仪、场发射电子扫描电镜-能谱分析对最终产物的物相组成及显微形貌进行检测。分析结果显示,过量的Mg、B_2O_3可有效提高产物中ZrB_2的含量,Mg和B_2O_3分别过量40%(质量分数)、30%(质量分数)为Mg-ZrO_2-B_2O_3体系的较佳配比。基于上述优化配比,研究了用无水硼砂(Na_2B_4O_7)替换原料中B_2O_3对产物ZrB_2含量及晶粒尺寸的影响,当替换量达到15%(质量分数)时,ZrB_2的含量最高,并且随着Na_2B_4O_7替换量的增加,产物的晶粒尺寸由2μm减小至不足0.5μm。 相似文献
14.
为提高C/C-SiC复合材料的超高温抗烧蚀性能,通过浆料涂刷和高温烧结相结合的方法在C/C-SiC复合材料表面制备了ZrB2-SiC复相陶瓷涂层,利用EDS、SEM对涂层的成分及微观形貌进行了分析。对涂层材料的力学性能和抗烧蚀性能进行了表征,结果表明:制备的ZrB2-SiC复相陶瓷涂层保护C/C-SiC复合材料的拉伸强度、弯曲强度及剪切强度分别为147 MPa、355 MPa和21.9 MPa,与无涂层保护的针刺C/C-SiC复合材料的力学性能相比略有下降。涂层材料具有良好的抗氧化烧蚀性能,经过热流密度为3 200 kW/m2的氧乙炔火焰烧蚀600 s试验,其线烧蚀率和质量烧蚀率分别为0.001 mm/s和0.0006 g/s。 相似文献
15.
AlN/ZrB2 multilayered coatings were synthesized in a magnetron sputtering system. The extensive measurements were employed to investigate the influence of different nanoscale modulation periods and modulation ratios on microstructure and mechanical properties of the coatings. Analysis of X-ray diffraction, profiler and nanoindention indicated that multilayered coatings possessed much higher hardness and elastic modulus than monolithic AlN and ZrB2 coatings. At the substrate negative bias of −80 V, maximum hardness (34.1 GPa) and elastic modulus (469.8 GPa) were obtained in the multilayer with Λ = 30 nm and tAlN:tZrB2 = 1:3. This hardest multilayer showed a marked polycrystalline structure with the strong mixture of ZrB2 (001), ZrB2 (100), ZrB2 (101), AlN (100) textures. 相似文献
16.
以ZrO2纤维、B2O3粉、Mg粉为原料,分别以NaCl、MgCl2及NaCl、MgCl2复合盐为稀释剂,采用模板辅助燃烧合成法,经酸洗制备了ZrB2短纤维,采用试算法计算了反应体系绝热温度,并对产物进行XRD和SEM表征。结果表明:反应体系的绝热温度随着熔盐掺量的增加而降低,掺NaCl体系绝热温度下降较为明显,尤其是在熔盐掺量较高的情况下。加入NaCl后产物物相主要为ZrB2以及少量残余的ZrO2,加入MgCl2后产物中还有少量Mg3B2O6。加入熔盐不仅能避免ZrO2纤维的熔融,使产物更容易保持原料中纤维的形状,还能减小产物的晶粒尺寸,加入MgCl2能促进产物晶粒的发育,随着MgCl2掺量的增加,纤维上的颗粒逐渐发育成棱角分明的六方状晶体。从残余的ZrO2含量和晶粒尺寸分析,单盐的效果要优于复合盐,MgCl2的效果优于NaCl。 相似文献
17.
ZrB2-SiC和Csf/ZrB2-SiC超高温陶瓷基复合材料烧蚀机理的研究 总被引:2,自引:0,他引:2
通过真空热压工艺制备了ZrB2-SiC材料和Csf(碳短纤维)/ZrB2-SiC超高温陶瓷基复合材料. 采用氧乙炔火焰在4186.8kW/m2的热流下分别喷吹烧蚀两种材料180s. ZrB2-SiC材料表面最高温度达到2406℃, 烧蚀后质量烧蚀率为-0.14%, 线烧蚀率为-1×10-3mm/s, Csf/ZrB2-SiC材料表面最高温度达到1883℃, 烧蚀后质量烧蚀率为-0.19%, 线烧蚀率为-4×10-4mm/s. 对两种材料烧蚀表面和剖面的分析发现, ZrB2-SiC材料烧蚀后由表及里依次形成了疏松ZrO2氧化层、SiC富集层和未反应层的三层结构, 其中SiC富集层能够起到抗氧化的作用. Csf/ZrB2-SiC 材料烧蚀后由外到内分别形成了ZrO2-SiO2氧化层、SiC耗尽层和未反应层的三层结构, 其中最外层以ZrO2为骨架, SiO2弥合其中的结构有效地阻挡了烧蚀中氧的侵入. 相似文献
18.
为了降低ZrB_2粉体的合成温度,并在此基础上合成粒径细小、纯度高的ZrB_2粉体,以ZrO2及B4C为原料,以Mg粉为还原剂,以NaCl-KCl为熔盐介质,研究熔盐镁热还原法低温合成ZrB_2超细粉体的工艺。探讨了反应温度、B/Zr物质的量比及Mg粉用量对合成ZrB_2超细粉体的影响,并对粉体的物相组成及显微结构进行了表征。结果表明合成ZrB_2的起始温度为1 173K,最佳合成温度为1 473K。合成纯相的ZrB_2粉体最佳工艺条件为:B/Zr物质的量比为2.2,Mg过量50%(质量分数),1 473K反应3h。所合成ZrB_2粉体的晶粒尺寸为30~300nm。 相似文献
19.
L.L. Martin 《Optical Materials》2011,33(5):738-741
The Ba2TiSi2O8 is a well known piezoelectric, ferroelectric and non-linear crystal. Nanocrystals of Ba2TiSi2O8 doped with 1.5 Dy3+ have been obtained by thermal treatment of a precursor glass and their optical properties have been studied. X-ray diffraction patterns and optical measurements have been carried out on the precursor glass and glass ceramic samples. The emission spectra corresponding to the Dy3+: 4F9/2 → 6H13/2 (575 nm), 4F9/2 → 6H11/2 (670 nm) and 4F9/2 → 6H9/2 (757 nm) transitions have been obtained under laser excitation at 473 nm. These measurements confirm the incorporation of the Dy3+ ions into the Ba2TiSi2O8 nanocrystals which produces an enhancement of luminescence at 575 nm. At this wavelength has been demonstrated a maximum optical amplification around 1.9 cm−1 (∼8.2 dB/cm). 相似文献
20.
Liuyi Xiang Fen WangJianfeng Zhu Xiaofeng Wang 《Materials Science and Engineering: A》2011,528(9):3337-3341
Al2O3/TiAl composites were successfully fabricated from powder mixtures of Ti, Al, TiO2 and Cr2O3 by a hot-press-assisted exothermic dispersion method. The effect of the Cr2O3 addition on the microstructures and mechanical properties of Al2O3/TiAl composites was characterized, and the results showed that the Rockwell hardness, flexural strength and fracture toughness of the composites increased as the Cr2O3 content increased. When the Cr2O3 content was 2.5 wt%, the flexural strength and the fracture toughness attained peak values of 925 MPa and 8.55 MPa m1/2, respectively. This improvement of mechanical properties was due to the more homogeneous and finer microstructure developed from the addition of Cr2O3 and an increase in the ratio of α2-Ti3Al to γ-TiAl matrix phases. 相似文献