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1.
Al2O3/Al2O3 joint was achieved using Ag-Cu-Ti + B + TiH2 composite fillers at 900 °C for 10 min. The evolution mechanism of interface during brazing was discussed. Effects of Ti and B atoms content on microstructure of joints were investigated. Results show that a continuous and compact reaction layer Ti3(Cu,Al)3O forms at Al2O3/brazing alloy interface. Ti(Cu,Al) precipitates near Ti3(Cu,Al)3O layer. In situ synthesized TiB whiskers evenly distribute in Ag and Cu based solid solution. The higher content of B powders in composite fillers increases TiB whiskers content, but decreases the thickness of Ti3(Cu,Al)3O layer, while the higher TiH2 powders content thickens Ti3(Cu,Al)3O layer. Ag and Cu based solid solutions become uniform and fine with the increasing of TiB whiskers content. Ti(Cu,Al) intermetallics content increase and they gradually distribute from Al2O3 side to the central of brazing alloy, but the content of Cu based solid solution decreases when the TiH2 content increases. 相似文献
2.
Porous aluminum oxide (Al2O3) preforms were formed by sintering in air at 1200 °C for 2 h. A356, 6061, and 1050 aluminum alloys were infiltrated into the preforms by squeeze casting in order to fabricate Al2O3/A356, Al2O3/6061, and Al2O3/1050 composites, respectively, with different volumes of aluminum alloy content. The content of aluminum alloy in the composites was 10–40% by volume. The resistivity of Al2O3/A356, Al2O3/6061, and Al2O3/1050 composites decreased dramatically from 6.41 × 1012 to 9.77 × 10−4, 7.28 × 10−4, and 6.24 × 10−4 Ω m, respectively, the four-points bending strength increased from 397 to 443, 435.1, 407.2 MPa, respectively, and the deviations were smaller than 2%. From SEM microstructural analysis and TEM bright field images, the pore volume fraction and the relative density of the composites were the most important factors that affected the physical and mechanical properties. The ceramic phase and alloy phase in Al2O3/aluminum alloy composites were found to be homogenized and uniformly distributed using electrical and mechanical properties analysis, microstructure analysis, and image analysis. 相似文献
3.
S.M. Lakiza Ja.S. TyschenkoL.M. Lopato 《Journal of the European Ceramic Society》2011,31(7):1285-1291
The phase diagram of the Al2O3-HfO2-Y2O3 system was first constructed in the temperature range 1200-2800 °C. The phase transformations in the system are completed in eutectic reactions. No ternary compounds or regions of appreciable solid solution were found in the components or binaries in this system. Four new ternary and three new quasibinary eutectics were found. The minimum melting temperature is 1755 °C and it corresponds to the ternary eutectic Al2O3 + HfO2 + Y3Al5O12. The solidus surface projection, the schematic of the alloy crystallization path and the vertical sections present the complete phase diagram of the Al2O3-HfO2-Y2O3 system. 相似文献
4.
Al2O3-SiC composite ceramics were prepared by pressureless sintering with and without the addition of MgO, TiO2 and Y2O3 as sintering aids. The effects of these compositional variables on final density and hardness were investigated. In the present article at first α-Al2O3 and β-SiC nano powders have been synthesized by sol-gel method separately by using AlCl3, TEOS and saccharose as precursors. Pressureless sintering was carried out in nitrogen atmosphere at 1600 °C and 1630 °C. The addition of 5 vol.% SiC to Al2O3 hindered densification. In contrast, the addition of nano MgO and nano TiO2 to Al2O3-5 vol.% SiC composites improved densification but Y2O3 did not have positive effect on sintering. Maximum density (97%) was achieved at 1630 °C. Vickers hardness was 17.7 GPa after sintering at 1630 °C. SEM revealed that the SiC particles were well distributed throughout the composite microstructures. The precursors and the resultant powders were characterized by XRD, STA and SEM. 相似文献
5.
Ipek AkinElif Yilmaz Filiz SahinOnuralp Yucel Gultekin Goller 《Ceramics International》2011,37(8):3273-3280
Alumina (Al2O3) and alumina-yttria stabilized zirconia (YSZ) composites containing 3 and 5 mass% ceria (CeO2) were prepared by spark plasma sintering (SPS) at temperatures of 1350-1400 °C for 300 s under a pressure of 40 MPa. Densification, microstructure and mechanical properties of the Al2O3 based composites were investigated. Fully dense composites with a relative density of approximately 99% were obtained. The grain growth of alumina was inhibited significantly by the addition of 10 vol% zirconia, and formation of elongated CeAl11O18 grains was observed in the ceria containing composites sintered at 1400 °C. Al2O3-YSZ composites without CeO2 had higher hardness than monolithic Al2O3 sintered body and the hardness of Al2O3-YSZ composites decreased from 20.3 GPa to 18.5 GPa when the content of ZrO2 increased from 10 to 30 vol%. The fracture toughness of Al2O3 increased from 2.8 MPa m1/2 to 5.6 MPa m1/2 with the addition of 10 vol% YSZ, and further addition resulted in higher fracture toughness values. The highest value of fracture toughness, 6.2 MPa m1/2, was achieved with the addition of 30 vol% YSZ. 相似文献
6.
在Cu-21Sn-12Ti钎料中添加不同质量分数的B粉制备Cu-Sn-Ti+B复合钎料,然后在钎焊温度910℃保温10 min条件下钎焊Al2O3与Ti-6Al-4V合金。研究了原位生成TiB对Al2O3/Ti-6Al-4V合金接头微观结构及力学性能的影响。接头中原位生成的TiB呈晶须状均匀分布在Ti2Cu上,当采用TiB体积分数低于40%的钎料钎焊Al2O3与Ti-6Al-4V合金时,均可获得连接良好且界面致密的钎焊接头。随接头中TiB的体积分数增加,Ⅱ区中的Ti2(Cu,Al)含量增加,并逐渐变得连续,TiB的分布区Ⅲ范围增宽,Ti-6Al-4V合金向钎料中的溶解量增加。接头的室温抗剪强度随TiB的体积分数增加先上升后下降,当接头中TiB体积分数增至20%时,接头抗剪强度达最大,为70.1MPa。 相似文献
7.
Sr3Al2O6 was synthesized via citric acid precursor. The effects of the molar ratio of citric acid to total metal cations concentration (CA/M) on the formation of Sr3Al2O6 were investigated. Increasing the CA/M promoted the formation of Sr3Al2O6. Single-phase and well-crystallized Sr3Al2O6 was obtained from the CA/M = 1, CA/M = 2 and CA/M = 4 precursor at temperature 1200 °C, 1100 °C and 900 °C, respectively. Differential thermal analysis and thermogravimetric (DTA/TG), X-ray diffractometry (XRD) and field emission scanning electron microscopy (FESEM) were used to characterize the precursors and the derived oxide powders. Sr3Al2O6 nanoparticles with a diameter of about 50-70 nm were obtained. 相似文献
8.
Khanh Quoc DangShinichi Takei Masakazu KawaharaMakoto Nanko 《Ceramics International》2011,37(3):957-963
Pulsed electric current sintering (PECS) was applied to obtain transparent ruby polycrystals. Al2O3-Cr2O3 powder mixture was prepared by drying an aqueous slurry consisting of Al2O3 and Cr(NO3)3 followed by PECS consolidation in vacuum at a sintering temperatures ranging from 1100 to 1300 °C with various heating rates between 2 and 100 °C/min and under an applied pressures from 40 to 100 MPa. Slow heating rate and high-pressure lead to highly densified and transparent Cr-doped Al2O3 polycrystals at sintering temperature of 1200 °C. 相似文献
9.
WC-40 vol.%Al2O3 composites were prepared by high energy ball milling followed by hot pressing. The tungsten carbide (WC) and commercial alumina (Al2O3) powders composed of amorphous Al2O3, boehmite (AlOOH) and χ-Al2O3 were used as the starting materials. The phase transformation during sintering, the influence of sintering temperature and holding time on the densification, microstructure, Vickers hardness and fracture toughness and the toughening effects of WC-40 vol.%Al2O3 composites were investigated. The results showed that the amorphous Al2O3, AlOOH and χ-Al2O3 were transformed to α-Al2O3 completely during the sintering process. With the increasing sintering temperature and holding time, the relative density increased and both the Vickers hardness and fracture toughness increased initially to the maximum values and then decreased. When the as milled powders were hot pressed at 1540 °C for 90 min, a relative density of 97.98% and a maximum hardness of 18.65 GPa with an excellent fracture toughness of 10.43 MPa m1/2 of WC-40 vol.%Al2O3 composites were obtained. 相似文献
10.
《Ceramics International》2016,42(8):9906-9912
Wetting behavior of molten Cu50Ti alloy on hexagonal BN (h-BN) and TiB2 ceramics has been studied under vacuum using a modified sessile drop method. Final contact angles of 8° and 3° are obtained at 1000 °C on h-BN and TiB2, respectively. Interaction occurs at the interface between the molten alloy and BN, leading to the formation of a reaction layer containing TiB and Ti nitrides. Interfacial interaction of Cu50Ti with TiB2 results in the formation of densely packed TiB layer about 60–100 μm thick and the detachment of TiB2 grains. Spreading wetting of liquid Cu50Ti on h-BN is mainly controlled by the reactions between Ti and BN at the triple line. For Cu50Ti/TiB2 system, spreading is mainly limited by the interfacial reaction in the first stage, and is possibly influenced by both the diffusion of boron atoms and viscous friction of the liquid in the second stage. Finally, brazing of graphite to CuCrZr alloy has been realized using Cu50TiH2 with ceramic additives (including BN and TiB2) as composite fillers. The joints exhibit favorable interfacial bonding between the filler layer and the substrates. The ceramic reinforcements in the filler layer could contribute to the improvement of the shear strength. 相似文献
11.
Gang WangHui Wang Weilong Li Zhaoyu RenJintao Bai Jinbo Bai 《Fuel Processing Technology》2011,92(3):531-540
Fe/Al2O3 catalysts with different Fe loadings (10-90 mol%) were prepared by hydrothermal method. Ethanol decomposition was studied over these Fe/Al2O3 catalysts at temperatures between 500 and 800 °C to produce hydrogen and multi-walled carbon nanotubes (MWCNTs) at the same time. The results showed that the catalytic activity and stability of Fe/Al2O3 depended strongly on the Fe loading and reaction temperature. The Fe(30 mol%)/Al2O3 and Fe(40 mol%)/Al2O3 were both the effective catalyst for ethanol decomposition into hydrogen and MWCNTs at 600 °C. Several reaction pathways were proposed to explain ethanol decomposition to produce hydrogen and carbon (including nanotube) at the same time. 相似文献
12.
Weiqi Yang Tiesong Lin Peng He Ming Zhu Changbao Song Dechang Jia Jicai Feng 《Journal of the American Ceramic Society》2013,96(12):3712-3719
An in situ short fiber reinforced brazing technique by taking advantage of reaction between ZrB2 and Ti has been developed for joining ZrB2–SiC ceramic and Ti6Al4V alloy. The Ag–Cu eutectic alloy was used as brazing interlayer to realize controllable growth of TiB in Ti‐rich environment. The microstructural evolution of the joint was divided into four stages as experiments performed from 840°C to 920°C. The diffusion behaviors of Ti and B may play an important role on the preferential growth of TiB whiskers during brazing. The statistics of the length of TiB showed that a rapid growth appeared at 880°C. The accommodation to the coefficients of thermal expansion by TiB whiskers was evaluated and the shear strength of the joints was tested. 相似文献
13.
Mehri Mashhadi Ehsan Taheri-NassajMaryam Mashhadi Vincenzo M. Sglavo 《Ceramics International》2011,37(8):3229-3235
The effects of Al addition on pressureless-sintering of B4C-TiB2 composites were studied. Different amounts of Al from 0% to 5 wt.% were added to B4C-TiB2 mixtures (containing up to 30 wt.% TiB2) and the samples were pressureless sintered at 2050 °C and 2150 °C under Ar atmosphere. Physical, microstructural and mechanical properties were analysed and correlated with TiB2 and Al additions and sintering temperature. Addition of Al to B4C-TiB2 results in increased shrinkage upon sintering and final relative density and lower porosity, the effect is being more evident when both Al and TiB2 are present. Fracture strength, elastic modulus and fracture toughness of 450 MPa, 500 GPa and 6.2 MPa.m1/2, respectively were measured. 相似文献
14.
A simple chemical bath method was used to deposit hydroxyapatite (HA) coatings on Al2O3, Ti, and Ti6Al4V substrates at ambient pressure by heating to 65–95 °C in an aqueous solution prepared with Ca(NO3)2·4H2O, KH2PO4, KOH, and EDTA. The deposition behavior, morphology, thickness, and phase of the coatings were investigated using scanning electron microscopy and X-ray diffractometry. The bonding strength of the coatings was measured using an epoxy resin method. The HA coatings deposited on the three kinds of substrates were fairly dense and uniform and exhibited good crystallinity without any additional heat treatment. A coating thickness of 1–1.8 μm was obtained for the samples coated once. By repeating the coating process three times, the thickness could be increased to 4.5 μm on the Al2O3 substrate. The bonding strength of these coatings was 18 MPa. 相似文献
15.
Huanping WangJinmin Chen Wenyi YangSiqiao Feng Hongping MaGuohua Jia Shiqing Xu 《Journal of the European Ceramic Society》2012,32(3):541-545
The effects of Al2O3 addition on the densification, structure and microwave dielectric properties of CaSiO3 ceramics have been investigated. The Al2O3 addition results in the presence of two distinct phases, e.g. Ca2Al2SiO7 and CaAl2Si2O8, which can restrict the growth of CaSiO3 grains by surrounding their boundaries and also improve the bulk density of CaSiO3-Al2O3 ceramics. However, excessive addition (≥2 wt%) of Al2O3 undermines the microwave dielectric properties of the title ceramics since the derived phases of Ca2Al2SiO7 and CaAl2Si2O8 have poor quality factor. The optimum amount of Al2O3 addition is found to be 1 wt%, and the derived CaSiO3-Al2O3 ceramic sintered at 1250 °C presents improved microwave dielectric properties of ?r = 6.66 and Q × f = 24,626 GHz, which is much better than those of pure CaSiO3 ceramic sintered at 1340 °C (Q × f = 13,109 GHz). 相似文献
16.
Preparation of the (Ti1−xNbx)2AlC solid solution (formed from the Mn+1AXn or MAX carbides, where n = 1, 2, or 3, M is an early transition metal, A is an A-group element, and X is C) with x = 0.2-0.8 was investigated by self-propagating high-temperature synthesis (SHS). Nearly single-phase (Ti,Nb)2AlC was produced through direct combustion of constituent elements. Due to the decrease of reaction exothermicity, the combustion temperature and reaction front velocity decreased with increasing Nb content of (Ti1−xNbx)2AlC formed from the elemental powder compacts. In addition, the samples composed of Ti, Al, Nb2O5, and Al4C3 were adopted for the in situ formation of Al2O3-added (Ti,Nb)2AlC. The SHS process of the Nb2O5/Al4C3-containing sample involved aluminothermic reduction of Nb2O5, which not only enhanced the reaction exothermicity but also facilitated the evolution of (Ti,Nb)2AlC. Based upon the XRD analysis, two intermediates, TiC and Nb2Al, were detected in the (Ti,Nb)2AlC/Al2O3 composite and their amounts were reduced by increasing the extent of thermite reduction involved in the SHS process. The laminated microstructure characteristic of the MAX carbide was observed for both monolithic and Al2O3-added (Ti,Nb)2AlC solid solutions synthesized in this study. 相似文献
17.
High burnup is a goal for further development of advanced nuclear power in the future. However, along with the increase of burnup, it becomes more diffidult to control reactor reactivity, which affects the operation safety of the nuclear reactor. Al2O3/B4C burnable poison materials widely used in pressurized water reactor currently will not meet the requirements of burnable poison materials in high burnup nuclear power. Because of the better performance of ZrO2/Gd2O3 burnable poison materials than that of Al2O3/B4C, this paper studies the preparation of ZrO2/Gd2O3 composite ceramic materials by the coprecipitation method. The experimental results show that at the sintering temperature of 1500–1650 °C, ZrO2/Gd2O3 composite ceramic grains are small, compact and uniform with the generation of homogeneous solid solution. At 1600 °C, ZrO2–10%Gd2O3 has the highest density and mechanical strength. 相似文献
18.
B. Fernández J.M. AlmanzaJ.L. Rodríguez D.A. CortesJ.C. Escobedo E.J. Gutiérrez 《Ceramics International》2011,37(8):2973-2979
The effects of V2O5, NiO, Fe2O3 and vanadium slag on the corrosion of Al2O3 and MgAl2O4 have been investigated. The specimens of Al2O3 and MgAl2O4 with the respective oxides above mentioned were heated at 10 °C/min from room temperature up to three different temperatures: 1400, 1450 and 1500 °C. The corrosion mechanisms of each system were followed by XRD and SEM analyses. The results obtained showed that Al2O3 was less affected by the studied oxides than MgAl2O4. Alumina was only attacked by NiO forming NiAl2O4 spinel, while the MgAl2O4 spinel was attacked by V2O5 forming MgV2O6. It was also observed that Fe2O3 and Mg, Ni, V and Fe present in the vanadium slag diffused into Al2O3. On the other hand, the Fe2O3 and Ca, S, Si, Na, Mg, V and Fe diffused into the MgAl2O4 structure. Finally, the results obtained were compared with those predicted by the FactSage software. 相似文献
19.
Studies on plasma sprayed bi-layered ceramic coating on bio-medical Ti-13Nb-13Zr alloy 总被引:1,自引:0,他引:1
S. SathishM. Geetha S.T. Aruna N. BalajiK.S. Rajam R. Asokamani 《Ceramics International》2011,37(4):1333-1339
Biomedical Ti alloys are prone to undergo degradation due to the combined effect of wear and corrosion. To overcome these problems, surface modification techniques are being used. In this paper, the biomedical Ti alloy Ti-13Nb-13Zr was plasma sprayed with nanostructured Al2O3-13 wt%TiO2, yttria stabilized zirconia powders and bilayer containing alternate layers of the two coatings to improve the corrosion resistance and microhardness of the substrate. The plasma sprayed coatings were characterized by X-ray diffraction, scanning electron microscopy and Raman spectroscopy. The microstructure, microhardness and surface roughness of the coatings were investigated. The corrosion resistance of the coatings was studied in simulated body conditions. The results show improved corrosion resistance for the bilayered coating compared to the individual plasma sprayed coatings on biomedical Ti-13Nb-13Zr alloy substrate. 相似文献
20.
S.E. LinW.C.J. Wei 《Journal of the European Ceramic Society》2011,31(16):3081-3086
Bismuth oxide in δ-phase is a well-known high oxygen ion conductor and can be used as an electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs). 5-10 mol% Ta2O5 are doped into Bi2O3 to stabilize δ-phase by solid state reaction process. One Bi2O3 sample (7.5TSB) was stabilized by 7.5 mol% Ta2O5 and exhibited single phase δ-Bi2O3-like (type I) phase. Thermo-mechanical analyzer (TMA), X-ray diffractometry (XRD), AC impedance and high-resolution transmission electron microscopy (HRTEM) were used to characterize the properties. The results showed that holding at 800-850 °C for 1 h was the appropriate sintering conditions to get dense samples. Obvious conductivity degradation phenomenon was obtained by 1000 h long-term treatment at 650 °C due to the formation of α-Bi2O3 phase and Bi3TaO7, and 〈1 1 1〉 vacancy ordering in Bi3TaO7 structure. 相似文献