共查询到20条相似文献,搜索用时 453 毫秒
1.
Yoshihiko Takano Masahiro Hachiya† Masaru Yoshinaka† Ken Hirota Osamu Yamaguchi 《Journal of the American Ceramic Society》2000,83(2):448-450
CrN powder consisting of granular particles of ∼3 μm has been prepared by self-propagating high-temperature synthesis under a nitrogen pressure of 12 MPa using Cr metal. Dense pure CrN ceramics and CrN/ZrO2 (2Y) composites in the CrN-rich region have been fabricated by hot isostatic pressing for 2 h at 1300°C and 196 MPa. The former ceramics have a fracture toughness ( K IC ) of 3.3 MPa ·m1/2 and a bending strength (σb ) of 400 MPa. In the latter materials almost all of the ZrO2 (2Y) grains (0.36–0.41 μm) are located in the grain boundaries of CrN (∼4.6 μm). The values of K IC (6.1 MPa · m1/2 ) and σb (1070 MPa) are obtained in the composites containing 50 vol% ZrO2 (2Y). 相似文献
2.
Masaru Yoshinaka Ken Hirota Masayuki Ito Hiroshi Takano Osamu Yamaguchi 《Journal of the American Ceramic Society》1999,82(1):216-218
Tin(IV) oxide (SnO2 ) crystallizes at room temperature by adding hydrazine monohydrate ((NH2 )2 · H2 O) to a hydrochloric acid solution of tin, followed by washing and drying. Well-densified SnO2 ceramics (99.8% of theoretical) with an average grain size of 0.9 μm have been fabricated by hot isostatic pressing for 2 h at 900°C and 196 MPa. Their Vickers hardness and bending strength are 14.4 GPa and 200 MPa, respectively. They exhibit an electrical conductivity of 2 × 10−3 −9 × 10−3 S·cm−1 at room temperature. 相似文献
3.
Yoshihiko Takano Tetsuya Komeda Masaru Yoshinaka Ken Hirota Osamu Yamaguchi 《Journal of the American Ceramic Society》1998,81(9):2497-2500
Intimate mixtures of Cr2 O3 /ZrO2 (2.5Y) in the Cr2 O3 -rich region are produced at low temperatures from amorphous materials prepared by the hydrazine method. Spark plasma sintering (SPS) has been performed for 10 min at 1300°C and 30 MPa. Composite ceramics with homogeneously dispersed fine ZrO2 (0.2 µm) give 99.8% of theoretical densities. Their mechanical properties are examined in connection with increased ZrO2 content. A high fracture toughness of 9.3 MPam1/2 and an excellent bending strength of 1290 MPa are achieved in the composite ceramics containing 50 mol% ZrO2 . 相似文献
4.
PAUL F. BECHER 《Journal of the American Ceramic Society》1983,66(7):485-488
Significant increases in the critical fracture toughness (K IC ) over that of alumina are obtained by the stress-induced phase transformation in partially stabilized ZrO2 particles which are dispersed in alumina. More importantly, improved slow crack growth resistance is observed in the alumina ceramics containing partially stabilized ZrO2 particles when the stress-induced phase transformation occurs. Thus, increasing the contribution of the ZrO2 phase transformation by tailoring the Y2 O3 stabilizer content not only increases the critical fracture toughness (KIC ) but also the K Ia to initiate slow crack growth. For example, crack velocities ( v )≥10–9 m/s are obtained only at K Ia ≥5 MPa.m1/2 in transformation-toughened ( K IC =8.5 MPa.m1/2 ) composites vs K Ia ≥2.7 MPa.m1/2 for comparable velocities in composites where the transformation does not occur ( K IC =4.5 MPa.m1/2 ). This behavior is a result of crack-tip shielding by the dissipation of strain energy in the transformation zone surrounding the crack. The stress corrosion parameter n is lower and A greater in these fine-grained composite materials than in fine-grained aluminas. This is a result of the residual tensile stresses associated with larger (≥1 μm) monoclinic ZrO2 particles which reside along the intergranular crack path. 相似文献
5.
Raymond A. Cutler Robert J. Mayhew Kevin M. Prettyman Anil V. Virkar 《Journal of the American Ceramic Society》1991,74(1):179-186
Simulataneous additions of SrO and Al2 O3 to ZrO2 (12 mol% CeO2 ) lead to the in situ formation of strontium aluminate (SrO · 6Al2 O3 ) platelets (∼0.5 μm in width and 5 to 10 μm in length) within the Ce-TZP matrix. These platelet-containing Ce-TZP ceramics have the strength (500 to 700 MPa) and hardness (13 to 14 GPa) of Ce-TZP/Al2 O3 while maintaining the high toughness (14 to 15 MPa ± m1/2 ) of Ce-TZP. Optimum room-temperature properties are obtained at SrO/Al2 O3 molar ratios between 0.025 and 0.1 for ZrO2 (12 mol% CeO2 ) with starting Al2 O3 contents ranging between 15 and 60 vol%. The role of various toughening mechanisms is discussed for these composite ceramics. 相似文献
6.
Yasuo Hikichi Toshitaka Ota Keiji Daimon Tomotoshi Hattori Masatoshi Mizuno 《Journal of the American Ceramic Society》1998,81(8):2216-2218
Xenotime-type RPO4 (R = Y, Er, Yb, or Lu) powder was dry-pressed into disks and bars. The disks and bars could be sintered to a relative density of greaterthan equal to98% in air without cracking at 1300° (R = Yb or Lu) or 1500°C (R = Y or Er), depending on the grain size. The linear thermal expansion coefficient (at 1000°C), thermal conductivity (at 20°C), and bending strength (at 20°C) of the xenotime-type RPO4 ceramics were 6.2 10-6 /°C, 12.02 W(mK)-1 , and 95 ± 29 MPa for R = Y; 6.0 10-6 /°C, 12.01 W(mK)-1 , and 100 ± 21 MPa for R = Er; 6.0 10-6 /°C, 11.71 W(mK)-1 , and 135 ± 34 MPa for R = Yb; and 6.2 10-6 /°C, 11.97 W(mK)-1 , and 155 ± 25 MPa for R = Lu. The xenotime-type RPO4 ceramics did not react with SiO2 , TiO2 , Al2 O3 , ZrO2 , or ZrSiO4 , even at 1600°C for 3 h in air, and were stable in aqueous solutions of HCl, H2 SO4 , HNO3 , NaOH, and NH4 OH at 20°C. 相似文献
7.
Noriyuki Yoshida Yoshihiko Takano Masaru Yoshinaka Ken Hirota Osamu Yamaguchi 《Journal of the American Ceramic Society》1998,81(8):2213-2215
Picrochromite (MgCr2 O4 ) crystallizes at 480° to 530°C from an amorphous material prepared by the hydrazine method. The MgCr2 O4 powders were characterized for particle size and surface area. Individual particles tend toward a hexagonal morphology above 1000°C. Dense MgCr2 O4 ceramics (99.5% of theoretical) with an average grain size of 2 μm have been fabricated by spark plasma sintering for 5 min at 1400°C and 30 MPa. Their fracture toughness and bending strength are 3.7 MPa·m1/2 and 310 MPa, respectively. 相似文献
8.
Yasuo Hikichi Tsuyoshi Nomura Yoshiya Tanimura Suguru Suzuki Masaaki Miyamoto 《Journal of the American Ceramic Society》1990,73(12):3594-3596
Monazite-type CePO4 powder (average grain size 0.3 μm) was dry-pressed to disks or bars. The green compacts began to sinter above 950°C. Relative density ≧ 99% and apparent porosity <1% were achieved when the specimens were sintered at 1500°C for 1 h in air. The linear thermal expansion coefficient and thermal conductivity of the CePO4 ceramics were 9 × 10−6 /°C to 11 × 10−6 /°C (200° to 1300°C) and 1.81 W/(m · K) (500°C), respectively. Bending strength of the ceramics (average grain size 4 μm) was 174 ± 28 MPa (room temperature). The CePO4 ceramics were cracked or decomposed by acidic or alkaline aqueous solutions at high temperatures. 相似文献
9.
Hong-Lim Lee Hun-Jin Lim Shin Kim Hyung-Bock Lee 《Journal of the American Ceramic Society》1989,72(8):1458-1461
β-Sialon powder was synthesized by the simultaneous reduction and nitridation of Hadong kaolin at 1350°C in an N2 –H2 atmosphere, using graphite as a reducing agent. The average particle size of β-sialon powder was about 4.5 μm. The synthesized β-sialon powder was pressureless sintered from 1450° to 1850°C under a N2 atmosphere. The relative density, modulus of rupture, fracture toughness, and microhardness of β-sialon ceramics sintered at 1800°C for 1 h were 92%, 248 MPa, 2.8 MN/m3/2 , and 13.3 GN/m2 , respectively. The critical temperature difference (ΔTc ) in water-quench thermal-shock behavior was about 375°C for the synthesized β-sialon ceramics. 相似文献
10.
Low-Temperature Fabrication of Cordierite Ceramics from Kaolinite and Magnesium Hydroxide Mixtures with Boron Oxide Additions 总被引:3,自引:0,他引:3
Katsuhiro Sumi Yuichi Kobayashi Etsuro Kato 《Journal of the American Ceramic Society》1999,82(3):783-785
Thermal reactions of mixtures of ultrafine particles of magnesium hydroxide (Mg(OH)2 ) and kaolinite in a composition of MgO:Al2 O3 :2SiO2 were investigated to obtain dense cordierite ceramics at temperatures <1000°C. While heating the mixture of kaolinite and Mg(OH)2 with the equivalent of 2 mass% of boron oxide (B2 O3 ) (in the form of magnesium borate, 2MgOB2 O3 ), an amorphous phase formed at a temperature of ∼850°C after thermal decomposition. Firing the mixture at a temperature of 900°C yielded dense ceramics with an apparent porosity of almost zero. The addition of B2 O3 promoted the densification at 850°-900°C and accelerated the crystallization of alpha-cordierite. The specimen with 3 mass% of B2 O3 that was fired at a temperature of 950°C showed a linear thermal expansion coefficient of ∼3 × 10−6 K−1 , a bending strength of >200 MPa, and a relative dielectric constant of 5.5 at 1 MHz. These cordierite ceramics may be used as substrate materials for semiconductor interconnection applications. 相似文献
11.
Dense, single-phase β-sialon ceramics were sintered at 1700°C and 200 MPa using the glass-encapsulated hot isostatic pressing technique. The materials were very hard, 1500 to 1700 kg / mm2 (98 N load), but were fairly brittle, with an indention fracture toughness of about 3 MPa · m1/2 . The addition of 1 wt% Y2 O3 before sintering had a positive effect on the toughness, especially at the low x compositions of Si3-x Alx Ox N4-x , where KIC ∼4 MPa · m1/2 . 相似文献
12.
Large-grained (100- to 200-μm), yttria-doped, polycrystalline t '-zirconia ceramics were fabricated by heat-treating presintered samples at temperatures 2100°C. Polarized light microscopy revealed the ferroelastic domain structure in the t ' samples. XRD showed that no monoclinic phase was detected on as-polished, ground and fracture surfaces, or on surfaces while under a tensile stress as high as 400 MPa. By contrast, relative changes occurred in the tetragonal peak intensities, which were attributed to ferroelasatic domain switching. The higher toughness of 3-mol%-Y2 O3 -doped t ' samples (7.7 MPa · m1/2 ) compared to that of 8 mol% Y2 O3 cubic samples (2.4 MPa · m1/2 ) was explained in part by ferroelastic domain switching. 相似文献
13.
In order to measure the elastic properties of titanium monoboride (TiB), which are not well known, a Ti/TiB composite with 95% volume fraction of TiB was fabricated by the powder metallurgy route. After compacting mixed Ti+TiB2 powders by a hot unidirectional pressure (1200°C, 25 MPa, 60 min, <10−2 Pa), annealing at 1200°C was performed for 48 h, after which the main phase in the material was TiB. The elastic properties of TiB were directly measured by using the nanoindentation technique. The polycrystalline modulus and hardness of the TiB were 450 and 27.5 GPa, respectively. 相似文献
14.
Gan Feng Tu Zhi Tong Sui Qiang Huang Chang Zhen Wang 《Journal of the American Ceramic Society》1992,75(4):1032-1034
Y-PSZ ceramics with 5 wt% Al2 O3 were synthesized by a sol–gel route. Experimental results show that powders of metastable tetragonal zirconia with 2.7 mol% Y2 O3 and 5 wt% Al2 O3 can be fabricated by decomposing the dry gel powder at 500°C. Materials sintered in an air atmosphere at 1500°C for 3 have high density (5.685 g/cm3 ), high content of metastable tetragonal zirconia (>96%), and high fracture toughness (8.67 MPa.m1/2 ). Compared with the Y-PSZ ceramics, significant toughening was achieved by adding 5 wt% Al2 O3 . 相似文献
15.
Shingo Hirano Masaru Yoshinaka Ken Hirota Osamu Yamaguchi 《Journal of the American Ceramic Society》1996,79(1):171-176
In the ZrO2 -Cr2 O3 system, metastable t -ZrO2 solid solutions containing up to 11 mol% Cr2 O3 crystallize at low temperatures from amorphous materials prepared by the hydrazine method. The lattice parameter c decreases linearly from 0.5149 to 0.5077 nm with increased Cr2 O3 content, whereas the lattice parameter a is a constant value ( a = 0.5077 nm) regardless of the starting composition. At higher temperatures, transformation (decomposition) of the solid solutions proceeds in the following way: t (ss)→ t (ss) + m + Cr2 O3 → m + Cr2 O3 . Above 11 mol% Cr2 O3 addition, c-ZrO2 phases are formed in the presence of Cr2 O3 . The t -ZrO2 solid solution powders have been characterized for particle size, shape, and surface area. They consist of very fine particles (15–30 nm) showing thin platelike morphology. Dense ZrO2 (3Y)-Cr2 O3 composite ceramics (∼99.7% of theoretical) with an average grain size of 0.3 μm have been fabricated by hot isostatic pressing for 2 h at 1400°C and 196 MPa. Their fracture toughness increases with increased Cr2 O3 content. The highest K Ic value of 9.5 MPa·;m1/2 is achieved in the composite ceramics containing 10 mol% Cr2 O3 . 相似文献
16.
The fracture strengths of sintered Al2 O3 containing 20 and 40 vol% ZrO2 (12 mol% CeO2 )—zirconia-toughened alumina (ZTA)—composites along with the fracture resistance can be increased (e.g., to ∼900 MPa and >12 Mpa·m1/2 , respectively), by increasing the mean grain size of the t -ZrO2 (and the Al2 O3 ) from ∼0.5 μm to ∼3 μm. At these lower t -ZrO2 contents, the fracture strength-fracture resistance curves show a continuous rise as opposed to the strength maxima observed in polycrystalline t -ZrO2 (12 mol% CeO2 ), CeTZP, and ZrO2 (12 mol% CeO2 ) ceramics containing ≤20 vol% Al2 O3 . The toughened composites also exhibit excellent damage resistance with fracture strengths of 500 MPa retained with surfaces containing ∼150- N Vickers indentations which produce cracks of ∼160-μm radius. Greater damage resistance correlates with an increase in the apparent R -curve response of these composites. 相似文献
17.
Effect of Iron and Boron Carbide on the Densification and Mechanical Properties of Titanium Diboride Ceramics 总被引:4,自引:0,他引:4
Eul Son Kang Cheol Woo Jang Chae Hyun Lee Chong Hee Kim Do Kyung Kim 《Journal of the American Ceramic Society》1989,72(10):1868-1872
The effect of Fe and B4 C on the sintering behavior and mechanical properties of TiB2 ceramics have been studied. Sintering was performed in an Ar atmosphere at 2000° using attrition-milled TiB2 powder (mean particle size = 0.8 μm). When a small amount of Fe (0.5 wt%) was added, abnormal grain growth occurred and the sintered density was low. In the case of B4 C added along with 0.5 wt% Fe, however, abnormal grain growth was remarkably suppressed, and the sintered density was increased up to 95% of theoretical. But with excess Fe addition (5 wt%), B4 C grains did not act as a grain growth inhibitor, and B4 C grains were frequently trapped in large TiB2 grains. The best mechanical properties were obtained for the TiB2 –10 wt% B4 C–0.5 wt% Fe ceramics, which exhibited a three-point bending strength of 400 MPa and a fracture toughness of 5.5 MPa · m1/2 . 相似文献
18.
Jiang Li Yubai Pan Yusong Wu Huamin Kou Jingkun Guo 《International Journal of Applied Ceramic Technology》2007,4(3):276-284
High-quality alumina ceramics were fabricated by a hot pressing with MgO and SiO2 as additives using α-Al2 O3 -seeded nanocrystalline γ-Al2 O3 powders as the raw material. Densification behavior, microstructure evolution, and mechanical properties of alumina were investigated from 1250°C to 1450°C. The seeded γ-Al2 O3 sintered to 98% relative density at 1300°C. Obvious grain growth was observed at 1400°C and plate-like grains formed at 1450°C. For the 1350°C hot-pressed alumina ceramics, the grain boundary regions were generally clean. Spinel and mullite formed in the triple-grain junction regions. The bending strength and fracture toughness were 565 MPa and 4.5 MPa·m1/2 , respectively. For the 1300°C sintered alumina ceramics, the corresponding values were 492 MPa and 4.9 MPa·m1/2 . 相似文献
19.
Rong-Jun Xie Mamoru Mitomo Kyota Uheda Fang-Fang Xu Yoshio Akimune 《Journal of the American Ceramic Society》2002,85(5):1229-1234
Rare-earth-doped oxynitride or nitride compounds have been reported to be luminescent and may then serve as new phosphors with good thermal and chemical stabilities. In this work, we report the photoluminescence (PL) spectra of europium-, terbium-, and praseodymium-doped Ca-α-SiAlON ceramics. The highly dense ceramics were prepared by hot pressing at 1750°C for 1 h under 20 MPa in a nitrogen atmosphere. Europium-doped Ca-α-SiAlON displayed a single broad emission band peaking at λ= 550–590 nm depending on the europium concentration. The emission bands in the spectra of europium-doped Ca-α-SiAlONs were assigned to the allowed transition of Eu2+ from the lowest crystal field component of 4 f 6 5 d to 8 S7/2 (4 f 7 ) ground-state level. The emission spectra of terbium- and praseodymium-doped Ca-α-SiAlON ceramics both consisted of several sharp lines, which were attributed to the 5 D4 →7 F j ( j = 3, 4, 5, 6) transitions of Tb3+ and 3 P0 →3 H j ( j = 3, 4, 5) transitions of Pr3+ , respectively. In particular, the terbium-doped α-SiAlON ceramics showed a strong green emission among these phosphors. 相似文献
20.
Thomas Richter Stefan Denneler Carsten Schuh Ender Suvaci Ralf Moos 《Journal of the American Ceramic Society》2008,91(3):929-933
A promising way to improve the performance of piezoelectric ceramics is grain orientation by templated grain growth. In this work lead-based piezoelectric ceramics Pb(Mg1/3 Nb2/3 )0.68 Ti0.32 O3 (PMN–32PT) and Pb(Mg1/3 Nb2/3 )0.42 (Ti0.638 Zr0.362 )0.58 O3 (PMN–37PT–21PZ) ceramics were textured via templated grain growth process. For texturization (001)-oriented BaTiO3 (BT) platelets (approximately 10 μm × 10 μm × 2 μm) were utilized as templates. The texturized ceramics were accomplished by aligning the templates by tape casting. The template growth into the matrix resulted in textured ceramics with Lotgering factors between 0.94 and 0.99 for both compositions. Consequences of the texture are enhanced dielectric and piezoelectric properties. Unipolar strain-field measurements of textured ceramics showed 0.25% strain s 33 at 3 kV/mm. Large signal d 33 * of up to 878 pm/V were determined directly from strain measurements. Compared with randomly oriented ceramics in texturized samples unipolar strain s 33 and large signal d 33 * was enhanced by a factor of up to 1.8. 相似文献