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1.
J.K. Sonber T.S.R.Ch. Murthy C. Subramanian Sunil Kumar R.K. Fotedar A.K. Suri 《International Journal of Refractory Metals and Hard Materials》2010
This paper presents the results of investigation carried out on synthesis and densification of monolithic HfB2 and the effect of TiSi2 as sinter additive. Pure phase HfB2 was prepared by boron carbide reduction of HfO2 and hot pressed to full density with the addition of TiSi2. Isothermal oxidation study of this composite was carried out at 850 °C up to 64 h. Formation of HfB2 was seen at 1200 °C but pure HfB2 was formed at a much higher temperature of 1875 °C in vacuum. Hot pressing of HfB2 at 1850 °C and 35 MPa pressure gave a compact of 80% TD. Addition of TiSi2 helped in achieving a much higher density at a lower temperature of 1600 °C and a pressure of 20 MPa. A fully dense composite of HfB2 and TiSi2 was obtained with 15% TiSi2. Hardness and fracture toughness of this composite were 27.4 ± 1.9 GPa and 6.6 ± 0.2 MPa m1/2, respectively. Considerable deflection was observed in the crack propagation in composites. Oxidation studies indicated the formation of HfO2, SiO2, TiO2 and HfSiO4 with some glassy phase and the composite with 15% TiSi2 was seen to be completely covered with a protective glassy layer. 相似文献
2.
Chuncheng Wei Xinghong ZhangPing Hu Wenbo HanShuang Li 《International Journal of Refractory Metals and Hard Materials》2012,30(1):173-176
Laminated ZrB2-SiC ceramics with ZrO2 interface layers were successfully prepared by tape casting, laminating and hot pressing. The flexural strength and fracture toughness are 561 ± 20 MPa and 14.4 ± 0.3 MPa m1/2 for parallel direction, and 432 ± 18 MPa and 5.8 ± 0.3 MPa m1/2 for perpendicular direction. The fracture toughness for parallel direction is improved significantly compared to monolithic ZrB2-SiC ceramics. The toughening mechanism was attributed to the deflection and branch of the crack and the new microcracks, which would increase the propagation path and fracture work. 相似文献
3.
Bulk WC-Al2O3 composites prepared by spark plasma sintering 总被引:1,自引:0,他引:1
Donghai ZhengXiaoqiang Li Xuan AiChao Yang Yuanyuan Li 《International Journal of Refractory Metals and Hard Materials》2012,30(1):51-56
WC and WC-Al2O3 materials without metallic binder addition were densified by spark plasma sintering in the range of 1800-1900 °C. The densification behavior, phase constitution, microstructure and mechanical properties of pure WC and WC-Al2O3 composite were investigated. The addition of Al2O3 facilitates sintering and increases the fracture toughness of the composites to a certain extent. An interesting phenomenon is found that a proper content of Al2O3 additive helps to limit the formation of W2C phase in sintered WC materials. The pure WC specimen possesses a hardness (HV10) of 25.71 GPa, fracture toughness of 4.54 MPa·m1/2, and transverse fracture strength of 862 MPa, while those of WC-6.8 vol.% Al2O3 composites are 24.48 GPa, 6.01 MPa·m1/2, and 1245 MPa respectively. The higher fracture toughness and transverse fracture strength of WC-6.8 vol.% Al2O3 are thought to result from the reduction of W2C phase, the crack-bridging by Al2O3 particles and the local change in fracture mode from intergranular to transgranular. 相似文献
4.
Fancheng MengCheng Liu Fan ZhangZhongqing Tian Weijiu Huang 《Journal of Alloys and Compounds》2012,512(1):63-67
Alumina matrix composites containing 5 and 10 wt% of ZrO2 were sintered under 100 MPa pressure by spark plasma sintering process. Alumina powder with an average particle size of 600 nm and yttria-stabilized zirconia with 16 at% of Y2O3 and with a particle size of 40 nm were used as starting materials. The influence of ZrO2 content and sintering temperature on microstructures and mechanical properties of the composites were investigated. All samples could be fully densified at a temperature lower than 1400 °C. The microstructure analysis indicated that the alumina grains had no significant growth (alumina size controlled in submicron level 0.66-0.79 μm), indicating that the zirconia particles provided a hindering effect on the grain growth of alumina. Vickers hardness and fracture toughness of composites increased with increasing ZrO2 content, and the samples containing 10 wt% of ZrO2 had the highest Vickers hardness of 18 GPa (5 kg load) and fracture toughness of 5.1 MPa m1/2. 相似文献
5.
Xin Sun Wenbo HanPing Hu Zhi WangXinghong Zhang 《International Journal of Refractory Metals and Hard Materials》2010
The high relative density of the ZrB2-based composite toughened by 25 vol.%Nb (ZN) was hot-pressed at reduced temperatures with low pressure of 30 MPa. Compared with the toughness of 2.3–3.5 MPa m1/2 and strength of 350 MPa of the monolithic ZrB2, the toughness and strength of the ZN composite were improved to 6.7 MPa m1/2 and 773 MPa, respectively, due to the addition of ductile Nb. The toughening mechanisms are crack deflection and branching as well as stress relaxation near the crack tip. Furthermore, the densification mechanism was analyzed and discussed. The results here pointed to a potential method for improving fracture toughness and strength of ZrB2-based ceramics. 相似文献
6.
WuBian Tian Hideki KitaHideki Hyuga Naoki Kondo 《Journal of Alloys and Compounds》2011,509(5):1819-1823
TiB2-C preforms formed with different compositions and processing parameters were reactively infiltrated by Si melts at 1450 °C to fabricate TiB2-SiC-Si composites. Phase constituent and microstructure of these composites were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The resulting composites are generally composed of TiB2 and reaction-formed β-SiC major phases, together with a quantity of residual Si. Unreacted carbon is detected in the samples with a starting composition of 2TiB2 + 1C formed at higher pressure and in all of the ones at the composition of 1TiB2 + 1C. The distribution of these phases is fairly homogeneous in microstructure. TiB2-SiC-Si composites show good mechanical properties, with representative values of 19.9 GPa in hardness, 395 GPa in elastic modulus, 3.5 MPa m1/2 in fracture toughness and 604 MPa in bending strength. The primary toughening and strengthening mechanism is attributed to the crack deflection of TiB2 particles. 相似文献
7.
Hailong Wang Deliang Chen Chang-An Wang Rui Zhang Daining Fang 《International Journal of Refractory Metals and Hard Materials》2009,27(6):1024-1026
ZrB2/Mo composites with various volume fractions of Mo (0–10%) were prepared by a hot-pressing process at 1950 °C. The addition of Mo both facilitated the densification and improved the mechanical properties of the ZrB2/Mo composites. Compared with the pure ZrB2 ceramics, the fracture toughness of the ZrB2/Mo (10%) composite increased from 4.52 to 7.98 MPa m1/2 and its bending strength increased from 424 to 450 MPa. The enhancement in mechanical properties of the ZrB2/Mo composites could be attributed to the reduced grains and the MoB phase formed in the reaction between ZrB2 and Mo. 相似文献
8.
The objective of this work is to produce Al2O3-ZrO2 composite from nano-sized powders processed by coprecipitation method. Al2O3 and mixture of Al2O3 + 10 wt.% ZrO2 precipitated successfully by chemical route from aluminum sulfate and zirconium sulfate were pressed under uniaxial compression of 170 MPa and sintered at 1600 °C for 1 h. SEM investigations revealed that, pure alumina sample has a microstructure with coarse grains which anisotropically grown up to 30-40 μm in size. In alumina-zirconia composite, the structure consists of very fine equiaxed grains of typically 2 μm in which zirconia precipitates were uniformly dispersed. By adding zirconia to alumina, hardness and indentation fracture toughness were increased from 11.6 GPa to 16.8 GPa and from 3.2 MPa m1/2 to 4.9 MPa m1/2, respectively. Improvement in fracture toughness was attributed to bridging effects of zirconia particles as well as transformation toughening. 相似文献
9.
《International Journal of Refractory Metals and Hard Materials》2011,29(5):601-607
Formation of ZrB2 by volume combustion synthesis (VCS) and mechanochemical process (MCP) from ZrO2-Mg-B2O3 was studied. Production of ZrB2 by VCS in air occurred with the formation of side products, Zr2ON2 and Mg3B2O6 in addition to MgO and ZrB2. Zr2ON2 formation was prevented by conducting VCS experiments under argon. Wet ball milling was applied to the VCS products before leaching for easier removal of Mg3B2O6 phase. MgO and Mg3B2O6 were removed from wet ball-milled products by leaching in 5 M HCl for 2.5 h. In MCP, 30-hour ball milling was found to be sufficient for the formation of ZrB2 with no minor phase formation. Leaching of MCP products in 1 M HCl for 30 min was sufficient to remove MgO. Complete conversion of ZrO2 to ZrB2 did not take place in both production methods, even with excess amounts of Mg and B2O3. Therefore, formed ZrB2 contained residual ZrO2. 相似文献
10.
Frédéric Monteverde 《Corrosion Science》2005,47(8):2020-2033
The resistance to oxidation in ambient air at a temperature up to 1600 °C of two hot-pressed diborides matrix composites, both containing 19.5% v/o SiC and 3 v/o HfN (as sintering aid), was investigated. The diboride matrix was based on HfB2 or a ZrB2/HfB2 mixture (volume ratio ≈ 1). Both the materials were subjected to repeated heating-cooling cycles at 1600 °C, and a 20 h exposure at 1450 °C in flowing dry air. Modest weight gains and limited corrosion depths highlighted a rather good thermal stability. In accordance with the thermo-gravimetric test at 1450 °C, the oxidation kinetics for both the composites superbly fit a para-linear law. The introduction of the SiC particles provided tangible benefits for the resistance to oxidation. One of the oxidation products, a borosilicate glass, sealed pores and coated the exposed faces, greatly limiting the inward transport of oxygen towards the internal oxide/diboride interfaces. 相似文献
11.
Ming He Shuren ZhangXiaohua Zhou Bo LiJing Wan 《Journal of Alloys and Compounds》2011,509(11):4260-4263
The behavior of dielectric and microwave properties against sintering temperature has been carried out on CaO-SiO2-B2O3 ceramic matrix composites with ZrO2 addition. The results indicated that ZrO2 addition was advantageous to improve the dielectric and microwave properties. X-ray diffraction (XRD) patterns show that the major crystalline β-CaSiO3 and a little SiO2 phase existed at the temperature ranging from 950 °C to 1050 °C. At 0.5 wt% ZrO2, CaO-SiO2-B2O3 ceramic matrix composites sintered at 1000 °C possess good dielectric properties: ?r = 5.85, tan δ = 1.59 × 10−4 (1 MHz) and excellent microwave properties: ?r = 5.52, Q · f = 28,487 GHz (11.11 GHz). The permittivity of Zr-doped CaO-SiO2-B2O3 ceramic matrix composites exhibited very little temperature dependence, which was less than ±2% over the temperature range of −50 to 150 °C. Moreover, the ZrO2-doped CaO-SiO2-B2O3 ceramic matrix composites have low permittivity below 5.5 over a wide frequency range from 20 Hz to 1 MHz. 相似文献
12.
Guobing YingXiaodong He Mingwei LiShanyi Du Wenbo HanFei He 《Journal of Alloys and Compounds》2011,509(31):8022-8027
In this work, phase pure Cr2AlC and impure Cr2AlC with Cr7C3 have been fabricated to investigate the mechanical, thermal, and electrical properties. The thermal expansion coefficient is determined as 1.25 × 10−5 K−1 in the temperature range of 25-1200 °C. The thermal conductivity of the Cr2AlC is 15.73 W/m K when it is measured at 200 °C. With increasing temperature from 25 °C to 900 °C, the electrical conductivity of Cr2AlC decreases from 1.8 × 106 Ω−1 m−1 to 5.6 × 105 Ω−1 m−1. For the impure phase of Cr7C3, it has a strengthening and embrittlement effect on the bulk Cr2AlC. And the Cr2AlC with Cr7C3 would result in a lower high-temperature thermal expansion coefficient, thermal conductivity, specific heat capacity and electrical conductivity. 相似文献
13.
Zipeng YanShu Cai Lijuan MiaoXing Zhou Yongming Zhao 《Journal of Alloys and Compounds》2012,511(1):101-106
Li2FeSiO4/C composites with in situ carbon coating were synthesized via sol-gel method based on acid-catalyzed hydrolysis/condensation of tetraethoxysilane (TEOS) with sucrose and l-ascorbic acid as carbon additives, respectively. As-obtained Li2FeSiO4/C composites prepared with l-ascorbic acid as a carbon additive are composed of nanoparticulate Li2FeSiO4 in an intimate contact with a continuous thin layer of residual carbon and exhibit large specific surface area up to 395.7 m2 g−1. The results indicate that structure of the residual carbon is graphene-rich with obviously lower disordered/graphene (D/G) ratio. These as-obtained Li2FeSiO4/C composites exhibit first discharge capacity of 135.3 mAh g−1 at C/16 and perform cycling stability, which are superior to those of Li2FeSiO4/C composites synthesized with sucrose as a carbon additive. 相似文献
14.
Jia SheYongzhong Zhan Mingjun PangChunliu Li Wenchao Yang 《International Journal of Refractory Metals and Hard Materials》2011,29(3):401-404
In the present work, novel zirconium matrix composites reinforced with ZrB2 or (ZrB2 + ZrC) hybrid short fibers were designed and prepared for the first time, through the reaction from Zr, B and B4C with non-consumable vacuum arc melting. The result shows that the ZrB2 particles grow in large short-fiber shape while the ZrC particles grow in thin short-fiber shape or near equiaxed shape. The morphological characters are related to their crystal structure and growth mechanism. Homogeneous distribution of both two in situ reinforcements can be found in the as-cast composites. As both the Zr matrix and the in situ reinforcements have good nuclear and mechanical properties, these Zr matrix composites are considered to be good candidates for applied as reactor core components. 相似文献
15.
Na LiLi Zhu Wei-De Zhang Yu-Xiang YuWen-Hui Zhang Mei-Fang Hou 《Journal of Alloys and Compounds》2011,509(41):9770-9775
In this work, TiO2 nanorods were prepared by a hydrothermal process and then Bi2MoO6 nanoparticles were deposited onto the TiO2 nanorods by a solvothermal process. The nanostructured Bi2MoO6/TiO2 composites were extensively characterized by X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy and UV-vis diffuse reflectance spectroscopy. The photocatalytic activity of the Bi2MoO6/TiO2 composites was evaluated by degradation of methylene blue. The Bi2MoO6/TiO2 composites exhibit higher catalytic activity than pure Bi2MoO6 and TiO2 for degradation of methylene blue under visible light irradiation (λ > 420 nm). Further investigation revealed that the ratio of Bi2MoO6 to TiO2 in the composites greatly influenced their photocatalytic activity. The experimental results indicated that the composite with Bi2MoO6:TiO2 = 1:3 exhibited the highest photocatalytic activity. The enhancement mechanism of the composite catalysts was also discussed. 相似文献
16.
Christian Sarra-Bournet Christine CharlesRod Boswell 《Surface & coatings technology》2011,205(15):3939-3946
TiO2 thin films were deposited on silicon wafer substrates by low-field (1 < B < 5 mT) helicon plasma assisted reactive sputtering in a mixture of pure argon and oxygen. The influence of the positive ion density on the substrate and the post-annealing treatment on the films density, refractive index, chemical composition and crystalline structure was analysed by reflectometry, Rutherford backscattering spectroscopy (RBS) and X-ray diffraction (XRD). Amorphous TiO2 was obtained for ion density on the substrate below 7 × 1016 m− 3. Increasing the ion density over 7 × 1016 m− 3 led to the formation of nanocrystalline (~ 15 nm) rutile phase TiO2. The post-annealing treatment of the films in air at 300 °C induced the complete crystallisation of the amorphous films to nanocrystals of anatase (~ 40 nm) while the rutile films shows no significant change meaning that they were already fully crystallised by the plasma process. All these results show an efficient process by low-field helicon plasma sputtering process to fabricate stoichiometric TiO2 thin films with amorphous or nanocrystalline rutile structure directly from low temperature plasma processing conditions and nanocrystalline anatase structure with a moderate annealing treatment. 相似文献
17.
The in situ oxidative template polymerization of aniline was performed successfully on the surface of negatively charged titania (TiO2) nanoparticles with a mean diameter of 40 nm using ammonium persulfate and a Chem-Solv solution at pH 1 and 25 °C. SEM showed that the resulting polyaniline (PANI)/TiO2 composites were well dispersed in solution due to the electrostatic repulsion force. Ultraviolet/visible spectroscopy, thermogravimetric analysis, Fourier-transform infrared spectroscopy, and cyclic voltammetry showed that the optical, thermal, and electrical properties of PANI/TiO2 composites were quite different from those of pure PANI or TiO2, which was attributed to the strong interaction between the two components. The conductivity of the PANI/TiO2 composite was estimated to be 0.91 × 10−1 S/cm at 25 °C in the range of semiconductor. 相似文献
18.
In this investigation, 3 mol% Y2O3 stabilized ZrO2-based composites reinforced with 10 vol.%, 20 vol.% and 40 vol.% WC (named as 3Y-TZP/10WC, 3Y-TZP/20WC and 3Y-TZP/40WC) were fabricated by using injection molding and sintering. Mechanical properties of these composites varied due to WC addition and dwelling time. Density, strength and toughness decreased with shorter dwelling time and increasing WC content however a significant enhancement in fracture toughness was obtained by 3Y-TZP/20WC composite which had 9.2 MPa m1/2 toughness. Severe unlubricated wear tests which were performed under 55 N normal load and 45 km sliding distance showed that 3Y-TZP/20WC composite had the lowest wear rate and wear volume values which are 2 × 10−8 mm3/(N m−1) and 0.05 mm3, respectively. 相似文献
19.
I. Khobta O. PetukhovO. Vasylkiv Y. SakkaA. Ragulya 《Journal of Alloys and Compounds》2011,509(5):1601-1606
The simultaneous synthesis and densification of TiN/TiB2 ceramic composites via reactive spark plasma sintering (RSPS) was investigated. Different component ratios (TiH2/BN (TiN, B)) and heating rates (112.5-300 °C/min) were used to initiate the chemical reaction for TiN/TiB2 synthesis. The omit RSPS process was revealed to have three stages, which are described separately. The relationships between the RSPS conditions, the microstructure and the properties of sintered ceramic composites were established. A Vickers hardness of 16-25 GPa and a fracture toughness of 4-6.5 MPa m1/2 were measured for various compositions. Sintered ceramic composites containing 36 wt% TiB2 with the highest relative density of 97.4 ± 0.4% and an average grain size of 150-550 nm have been obtained. 相似文献
20.
Piezoelectric and dielectric properties of Dy2O3-doped (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free ceramics
Chen Zhi-hui Ding Jian-ning Mei LinYuan Ning-yi Zhu Yuan-yuan 《Journal of Alloys and Compounds》2011,509(2):482-485
(Bi0.5Na0.5)0.94Ba0.06TiO3 + x wt% Dy2O3 with x = 0-0.3 ceramics were synthesized by conventional solid-state processes. The effects of Dy2O3 on the microstructure, the piezoelectric and dielectric properties were investigated. X-ray diffraction pattern confirmed that the coexistence of tetragonal and rhombohedral phases in the (Bi0.5Na0.5)0.94Ba0.06TiO3 composition was not changed by adding 0.05-0.3 wt% Dy2O3. SEM images indicate that all the ceramics have pore-free microstructures with high density, and that doping of Dy2O3 inhibits the grain growth of the ceramics. The addition of Dy2O3 shows the double effects on decreasing the piezoelectric and dielectric properties for 0 < x < 0.15 when Dy3+ ions substitute B-site Ti4+ ions, and increasing the properties for 0.15 < x < 0.3 when Dy3+ ions enters into A-site of the perovskite structure. The optimum electric properties of piezoelectric constant d33 = 170 pC/N and the dielectric constant ?r = 1900 (at a frequency of 1 kHz) are obtained at x = 0.3. 相似文献