共查询到20条相似文献,搜索用时 15 毫秒
1.
Kenji Hatanaka Masashi Katsuyama Hideki Takagi 《Journal of the American Ceramic Society》2003,86(1):135-140
The fatigue tests under push-pull completely reversed loading and pulsating loading were performed for silicon nitride ceramics at elevated temperatures. Then the effects of stress wave form, stress rate, and cyclic understressing on fatigue strength, and cyclic straining behavior, were examined. The cycle-number-based fatigue life is found to be shorter under trapezoidal stress wave loading than under triangular stress wave loading, and to become shorter with increasing hold time under the trapezoidal stress wave loading. Meanwhile, the equivalent time-based life curve, which is estimated from the concept of slow crack growth, almost agrees with the static fatigue life curve in the short and intermediate life regions, showing the small cyclic stress effect and the dominant stress-imposing period effect on cyclic fatigue life. The fatigue strength increased in stepwise stress amplitude increasing test, where stress amplitude is increased stepwise every given number of stress cycles, at 1100° and 1200°C. Occurrence of cyclic strengthening was proved through a gradual decrease in strain amplitude during a pulsating loading test at 1200°C in this material, corresponding to the above cyclic understressing effect on fatigue strength. 相似文献
2.
Oxidation Behavior and Flexural Strength of Aluminum Nitride Exposed to Air at Elevated Temperatures 总被引:1,自引:0,他引:1
The oxidation behavior of a sintered aluminum nitride containing 3 wt% Y2 O3 as a sintering aid was investigated. Samples were exposed to air at elevated temperatures for times up to 100 h. The weights of the samples were continuously monitored during exposure at various temperatures and humidity levels. The effects of oxidation on room-temperature flexural strength were also determined, and correlated to the observed weight changes of the samples. At temperatures 1200°C, linear weight gains were observed. However, at temperatures above 1200°C, the weight gains became parabolic with respect to exposure time. The oxidation rates were significantly increased by water vapor in the air. The oxidation products were found by X-ray analysis to be a mixture of Al2 O3 and 5A12 O3 ·3Y2 O3 . The oxide layer formed on the surface was severely cracked because of the thermal expansion mismatch between the oxide layer and the substrate. The cracks initiated in the oxide layer and propagated into the substrate, resulting in severe reduction in the room-temperature flexural strength of the material. When exposed to ambient air for more than 50 h at temperatures greater than 1100°C, the strengths of the samples decreased to less than half that of the as-received material. 相似文献
3.
Oxidation Kinetics of Aluminum Nitride 总被引:1,自引:0,他引:1
Darbha Suryanarayana 《Journal of the American Ceramic Society》1990,73(4):1108-1110
Thermal oxidation kinetics of aluminum nitride (AlN) powders, having fine- and coarse-particle-size distributions, were studied using thermogravimetric analysis (TGA). The kinetics showed dependence on the particle-size parameter, and the experimental TGA data were curve fitted using empirical mass relations employing both linear and parabolic models. The simulations predicted mixed kinetics in AlN oxidation. 相似文献
4.
Zheng Gu James H. Edgar Chongmin Wang Dorothy W. Coffey 《Journal of the American Ceramic Society》2006,89(7):2167-2171
The oxidation kinetics, morphology, and crystallinity of aluminum nitride (AlN) powder thermally oxidized in flowing oxygen were determined from 800° to 1150°C. At 800°C the oxidation became detectable with weight change. AlN powder was almost completely oxidized at 1050°C after only 0.5 h. Amorphous aluminum oxide formed at relatively low temperatures (800°–1000°C), with a linear oxidation rate governed by the oxygen–nitride interfacial reaction. Transmission electron microscopy displayed individual aluminum oxide grains which formed a discontinuous oxide layer at this temperature range. The aluminum oxide was crystalline at higher temperatures (>1000°C), as detected by X-ray diffraction, and the density of oxide grains increased with temperature. 相似文献
5.
氮化铝复合材料的氧化 总被引:1,自引:0,他引:1
制订出在广泛的温度范围(1073~1273K)及时间范围内研究氮化铝质陶瓷复合材料在空气中的耐热性能的方法,并且试样重量变化的绝对误差不大于0.15~0.17mg。采用重力测量法研究了氮化铝质复合材料与磷酸盐结合剂之间的相互作用,并与热压试样进行了比较。提出了结合剂性能对氧化过程动力学的影响机理。氧化过程的活化能值较低(152~205KJ·mol-1),因此可以推断材料氧化过程的速度将取决于铝离子通过α-Al2O3膜时的扩散状况。 相似文献
6.
The effects of rare-earth oxide additions on the oxidation of sintered Si3 N4 were examined. Insignificant oxidation occurred at 700o and 1000oC, with no evidence of phase instability. At 1372oC, the oxidation rate was lowest for Y203 and increased for additions of La2 O3 , Sm2 O3 , and CeO2 , in that order. Data obtained from X-ray diffraction, electron microprobe analysis, and scanning electron microscopy indicate that oxidation occurs via diffusion of cationic species from Si3 N4 grain boundaries. 相似文献
7.
Beketov A. R. Beketov D. A. Khoroshavin L. B. Chebykin V. V. 《Refractories and Industrial Ceramics》2002,43(3-4):122-126
A method for studying the heat resistance of composite aluminum nitride-based ceramic materials in air at 1073 – 1273 K is developed that allows the change in mass to be measured with an accuracy of 0.15 – 0.17 mg. The interaction between AlN-based composite materials and a phosphate binder (H3PO4) is studied and compared with hot-pressed specimens. A mechanism for the effect of the binder on the kinetics of oxidation is proposed. The relatively low activation energies (152 and 205 kJ/mole) suggest that the oxidation process is mainly determined by the diffusion of aluminum ions through the -Al2O3 film. 相似文献
8.
Else Breval Michael K. Aghajanian John P. Biel Stanislav Antolin 《Journal of the American Ceramic Society》1993,76(7):1865-1868
Unreinforced AlN/Al ceramic/metal composites were produced by the directed oxidation of molten Al alloys in nitrogen. The microstructures of these composites were compared with those of previously studied Al2 O3 /Al composites. In both composite systems the ceramic phase was interconnected and oriented in a columnar structure. The metallic phase showed no significant crystallographic orientation and appeared as both interconnected channels and isolated inclusions. The columns in the nitride system were found to be of micrometer size and to contain subgrains weakly defined by lattice defects, unlike the oxide system, where the columnar structure was shown to be of millimeter size and to contain well-defined micrometer-sized subgrains. Finer structures were obtained in both systems via the addition of Ni to the parent alloy. 相似文献
9.
Kwang Joo Kim Kwang‐Young Lim Young‐Wook Kim 《Journal of the American Ceramic Society》2013,96(11):3463-3469
The electrical properties of β‐SiC ceramics were found to be adjustable through appropriate AlN–Y2O3 codoping. Polycrystalline β‐SiC specimens were obtained by hot pressing silicon carbide (SiC) powder mixtures containing AlN and Y2O3 as sintering additives in a nitrogen atmosphere. The electrical resistivity of the SiC specimens, which exhibited n‐type character, increased with AlN doping and decreased with Y2O3 doping. The increase in resistivity is attributed to Al‐derived acceptors trapping carriers excited from the N‐derived donors. The results suggest that the electrical resistivity of the β‐SiC ceramics may be varied in the 104–10?3 Ω·cm range by manipulating the compensation of the two impurity states. The photoluminescence (PL) spectrum of the specimens was found to evolve with the addition of dopants. The presence of N‐donor and Al‐acceptor states within the band gap of 3C–SiC could be identified by analyzing the PL data. 相似文献
10.
Makoto Egashira Yasuhiro ShImizu Yuji Takao Ryoji Yamaguchi Yasuhiro Ishikawa 《Journal of the American Ceramic Society》1994,77(7):1793-1798
To suppress the reactivity of ALN powder with water, chemical surface modification with carboxylic acids has been investigated. It was found that the chemical stability of ALN powder increased as the number of carbon atoms in carboxylic acids used for the surface treatment increased. Among the carboxylic acids tested, stearic acid was the most promising from the viewpoint of the chemical stability of the treated powder and the thermal conductivity of the sintered ceramics prepared by cold isostatic pressing and pres-sureless sintering. 相似文献
11.
The modified static loading technique for estimating static fatigue limits was used to study the effects of oxidation and temperature on the static fatigue limit, K 10 for crack growth in sintered silicon carbide. For as-machined, unoxidized sintered silicon carbide with a static load time of 4 h, K 10 × 2.25 MPa * m1/2 at 1200° and ∼1.75 at 1400°C. On oxidation for 10 h at 1200°C, K 10 drops to ∼1.75 MPam1/2 at 1200° and ∼1.25 at 1400°C when tested in a nonoxidizing ambient. Similar results were obtained at 1200°C for tests performed in air. A tendency for strengthening below the static fatigue limit appears to result from plastic relaxation of stress in the crack-tip region by viscous deformation involving an oxide grain-boundary phase for oxidized material and, possibly, diffusive creep deformation in the case of unoxidized material. 相似文献
12.
Structural Reliability of Yttria-Doped Hot-Pressed Silicon Nitride at Elevated Temperatures 总被引:1,自引:0,他引:1
The strength of yttria-doped hot-pressed silicon nitride was investigated as a function of temperature, time, and applied load. Data collected at 1200°C are presented in the form of a strength-degradation diagram for an applied stress of 350 MPa. At this temperature, the behavior of yttria-doped hot-pressed silicon nitride is found to be superior to that of magnesia-doped hot-pressed silicon nitride, in which creep results in the formation of microcracks that lead to strength degradation. By contrast, the yttria-doped material does not suffer from microcrack formation or strength degradation at 1200°C. Strength degradation does occur at higher temperatures and, as a consequence, an upper limit of 1200°C is recommended for yttria-doped hot-pressed silicon nitride in structural applications. 相似文献
13.
Isao Tanaka Giuseppe Pezzotti Ken-ichi Matsushita Yoshinari Miyamoto Taira Okamoto 《Journal of the American Ceramic Society》1991,74(4):752-759
The effect of trace impurities on high-temperature strength is examined in Si3 N4 sintered without additives. Strength degradation above 1000°C occurs only in the low-purity material, which also exhibits an intergranular slow crack growth (SCG) rate 2 orders of magnitude faster than that of the high-purity material at 1400°C. A relaxation peak of internal friction is observed only in the low-purity material, at ≅1200°C, and the origin of this peak is ascribed to the initial stage of SCG—that is, the cavity-nucleation stage, enhanced by impurities. Based on the present results, a model for impurity-enhanced SCG is proposed. 相似文献
14.
Akira Nakayama Shinji Nambu Masahiro Inagaki Masahiko Miyauchi Nobuyuki Itoh 《Journal of the American Ceramic Society》1996,79(6):1453-1456
Complex permittivity of polycrystalline AlN was measured over the frequency range 100 MHz to 13 GHz using reflection coefficient and cavity resonator methods. Dielectric relaxation peaks of loss tangent were observed in the frequency range 200 MHz to 3 GHz. The maximum value of loss tangent was ∼200 × 10−4 . Relative permittivities decreased by ∼4% with increased frequency at the region of relaxation peaks. It was shown that these dispersion frequencies were inversely proportional to the grain sizes of AlN and independent of purities and processes. Model calculations for elastic vibration of a single-crystal grain of AlN were performed to investigate the origin of the dielectric dispersion due to piezoelectric effect. The calculated results of elastic sphere and 14-faced-polyhedron models showed a good quantitative agreement with the observed dispersion frequencies, which suggested that the dispersion was due to a piezoelectric vibration of a single grain of AlN ceramics at microwave frequencies. 相似文献
15.
Oxidation Behavior of Titanium Boride at Elevated Temperatures 总被引:3,自引:0,他引:3
Young-Hag Koh Seung-Yong Lee Hyoun-Ee Kim 《Journal of the American Ceramic Society》2001,84(1):239-241
The oxidation behavior of dense TiB2 specimens was investigated. Hot-pressed TiB2 with 2.5 wt% Si3 N4 as a sintering aid was exposed to air at temperatures between 800° and 1200°C for up to 10 h. The TiB2 exhibited two distinct oxidation behaviors depending on the temperature. At temperatures below 1000°C, parabolic weight gains were observed as a result of the formation of TiO2 ( s ) and B2 O3 ( l ) on the surface. The oxidation layer comprised two layers: an inner layer of crystalline TiO2 and an outer layer mainly composed of B2 O3 . When the oxidation temperatures were higher than 1000°C, gaseous B2 O3 was formed along with crystalline TiO2 by the oxidation process. In this case, the surface was covered with large TiO2 grains imbedded in a highly textured small TiO2 matrix. 相似文献
16.
Hot Isostatic Pressing of Sintered Silicon Nitride 总被引:1,自引:0,他引:1
Pressureless-sintered silicon nitride with varying additives was hot isostatic pressed under 150 MPa of nitrogen at 1800°C. Moderate increases in densities were observed when sintered densities exceeded 90% of theoretical. However, density changes became insignificant as the amount of additives exceeded 12 wt%; moreover, density reduction was occasionally observed. Microstructural analysis, after the silicon nitride was reannealed at 1650°C under 0.1 MPa of nitrogen, revealed that intergranular glass was supersaturated with nitrogen and "bloated" as a result of nitrogen evolution. This result suggested that the effectiveness of container-free hot isostatic pressing of silicon nitride was severely limited by enhanced solubility of nitrogen gas in the glassy phase under high pressure. 相似文献
17.
Creep Behavior of a Sintered Silicon Nitride 总被引:1,自引:0,他引:1
Margaret M. Chadwick Robert S. Jupp David S. Wilkinson 《Journal of the American Ceramic Society》1993,76(2):385-396
A commercial sintered silicon nitride has been crept in bending and compression at temperatures of 1100°C to 1400°C. In the as-sintered condition the material contains an amorphous intergranular phase. This phase undergoes partial devitrification as a result of high temperature exposure. Preannealing the material to a stable microstructure has very little effect on the creep properties. Deformation behavior compares well with that predicted from a model for creep due to viscous flow of a non-Newtonian grain boundary phase. In bending, the model predicts an initial constant strain rate at low strains as the intergranular phase is squeezed out from between grains under compression. Samples crept in compression are not expected to have this same initial constant strain rate regime. The model also predicts a strong initial strain rate dependence (in bending) on the initial thickness of the amorphous grain boundary layer. Experimentally this strain rate is not affected by partial grain boundary crystallization, suggesting that partial devitrification does not alter the intergranular film thickness or viscosity. This is supported by transmission electron microscopy, which has shown that crystallization of the intergranular phase occurs largely in the pockets between grains, leaving amorphous films between grains. 相似文献
18.
John A. Hanigofsky Karren L. More W. J. Lackey Woo Y. Lee Garth B. Freeman 《Journal of the American Ceramic Society》1991,74(2):301-305
The composition and microstructure of dispersed-phase ceramic composites containing BN and AIN as well as BN and AIN single-phase ceramics prepared by chemical vapor deposition have been characterized using X-ray diffraction, scanning electron microscopy, electron microprobe, and transmission electron microscopy techniques. Under certain processing conditions, the codeposited coating microstructure consists of small single-crystal AIN fibers (whiskers) surrounded by a turbostratic BN matrix. Other processing conditions resulted in single-phase films of AIN with a fibrous structure. The compositions of the codeposits range from 2 to 50 mol% BN, 50 to 80 mol% AIN with 7% to 25% oxygen impurity as determined by electron microprobe analysis. 相似文献
19.
Static and Cyclic Fatigue Behavior of a Sintered Silicon Nitride at Room Temperature 总被引:2,自引:0,他引:2
The static and cyclic fatigue behavior of sintered silicon nitride was investigated at room temperature. Flexure specimens, with an indentation-induced flaw at the center, were tested under a static or cyclic load applied by four-point bending. Sintered silicon nitride was shown to be susceptible to static and cyclic fatigue failure. Comparing the static and cyclic fatigue lifetimes at frequencies from 0.01 to 10 H z , it was shown that minimum time to failure was almost the same, in spite of differences in loading mode or frequency. However, cyclic stress decreased the scatter in lifetime by reducing the upper limit. Moreover, the cyclic fatigue limit was significantly lower than the static fatigue limit. High-magnification fractography revealed a fatigue failure dominated by intergranular cracking with partial transgranular failure at perpendicularly elongated crystals. This suggests that the intergranular fatigue crack can be arrested at grain-boundary triplets, and also can be reactivated by subsequent cyclic loading. The crack growth rate, calculated from the fatigue lifetime, showed three characteristic regions having a plateau at 70% to 90% of the fracture toughness, which suggests a possible intergranular stress corrosion cracking mechanism resembling that in glass or alumina. 相似文献
20.
MgO-C耐火材料在不同温度下于空气中的氧化机理 总被引:1,自引:0,他引:1
在空气中,于800-1600℃的不同温度下,定期采用测量重量损失的方法对含20%(质量)石墨MgO-C耐火材料的氧化进行了研究。随着温度从800℃升高到1400℃,脱碳率提高,然后从1400℃-1600℃或多或少保持恒定。详细地分析了氧化动力学,并且从800℃-1400℃的湿度范围得到了反应速度模型,发现可以通过脱碳层的氧护散来控制反应速度。在较高的温度(>1400℃)下,通过MgO(固)+C(固)→Mg(气)+CO(气)反应间接地发生石墨氧化,这样产生的镁气体在耐火材料的外表面再发生氧化,并作为MgO沉积。这会导致在脱碳的外壳中气孔率降低,结果氧化速度放慢。 相似文献