共查询到20条相似文献,搜索用时 15 毫秒
1.
Wei-wu Chen Wei-ying Sun Pei-ling Wang Ya-wen Li Yi-Bing Cheng Dong-sheng Yan 《Journal of the American Ceramic Society》2002,85(1):276-278
The effects of sintering cycles and doping elements on the microstructures of Ln-α-sialon were studied. The results showed that microstructures with an elongated α-sialon morphology could be obtained through high-temperature post-heat treatment (1800–1900°C) or by prolonging soaking times during sintering. Different rare-earth elements had a profound effect on the microstructure of the resulting α-sialon. The Ln-α-sialon doped with low- Z -value elements could easily develop elongated grains with higher aspect ratio. 相似文献
2.
Joosun Kim Anatoly Rosenflanz I-Wei Chen 《Journal of the American Ceramic Society》2000,83(7):1819-1821
Single-phase α-SiAlON with elongated grains is obtained from α-Si3 N4 powder for a broad range of compositions of practical interest. Following the concept of nucleation and growth, two-step firing is used for microstructure control. This method takes advantage of the slow transformation reaction from α-Si3 N4 to α-SiAlON at low temperature when the composition is near the α-SiAlON phase boundary and, hence, is marginally stable. For more-stable compositions, the seeding of α-SiAlON crystals is more effective, because it allows elongated grains to grow onto the seed crystals. The fracture toughness is strongly correlated with the microstructure and is enhanced greatly in the optimized materials. 相似文献
3.
Rong-Jun Xie Naoto Hirosaki Mamoru Mitomo Yoshinobu Yamamoto Takayuki Suehiro Naoki Ohashi 《Journal of the American Ceramic Society》2004,87(7):1368-1370
Cerium-doped α-SiAlON (M x Si12−( m + n ) Al m + n O n N16– n ) materials have been prepared by gas-pressure sintering and post-hot-isostatic-press (HIP) annealing, using four powder mixtures of α-Si3 N4 , AlN, and either (i) CeO2 , (ii) CeO2 + Y-α-SiAlON seed, (iii) CeO2 + Y2 O3 , or (iv) CeO2 + CaO. Cerium-containing CeAl(Si6– z Al z )(N10– z O z ) (JEM) phase, rather than Ce-α-SiAlON phase, forms in the sample with only CeO2 , whereas a single-phase α-SiAlON generates in samples with dual doping (CeO2 + Y2 O3 and CeO2 + CaO). On ultraviolet-light excitation, JEM gives one broad emission band with maximum at 465 nm and a shoulder at 498 nm; α-SiAlON shows an intense and broad emission band that peaks at 500 nm. The unusual long-wavelength emissions in JEM and α-SiAlON are due to increases in the nephelauxetic effect and the ligand-field splitting of the 5 d band, because the coordination of Ce3+ in JEM and α-SiAlON is nitrogen enriched. 相似文献
4.
Misha Zenotchkine Roman Shuba Joo Sun Kim I-Wei Chen 《Journal of the American Ceramic Society》2001,84(4):884-886
R -curves of single-phase Y- and Ca-containing α-SiAlON ceramics have been measured. They range from flat ones for fine-grain ceramics to pronounced rising ones when large elongated grains are present. The highest toughness measured reached 11.5 MPa·m1/2 over a crack extension of about 1000 μm. 相似文献
5.
Xin Xu Marta I. L. L. Oliveira José M. F. Ferreira 《Journal of the American Ceramic Society》2003,86(2):366-368
Dense α-SiAlON ceramics were obtained by pressureless sintering of green compacts prepared using slip casting. The rheological properties of the reaction SiAlON suspension were optimized to achieve a high degree of dispersion with a high solids volume fraction, which resulted in homogeneous and relatively dense green bodies with high sintering ability, which could be densified by pressureless sintering at 1750°C for 2 h. The sintered samples revealed a high degree of uniformity and almost fully dense microstructures that consisted of many small, elongated grains homogeneously dispersed in the fracture surfaces, which had properties comparable with those of other SiAlONs obtained using hot pressing. 相似文献
6.
Single-phase small crystals of Li-, Mg-, Ca-, Y-, Nd-, and Yb-α-SiAlONs have been obtained by liquid-phase sintering for various compositions and processing conditions. These crystals are suitable for seeding grain growth in α-SiAlON ceramics. The influence of chemical and processing parameters (starting composition and powders, green density, liquid content, heating schedule, nitrogen pressure, and temperature) on the size and morphology of seed crystals has been investigated. The results are compared with those for β-Si3 N4 crystal formation, and the differences are discussed in terms of nucleation and growth kinetics during liquid-phase sintering. 相似文献
7.
Three calcium α-SiAlON microstructures—namely, fine-grained, bimodal, and large elongated—were developed using powders of the same composition and then characterized. The evolution of grain size and morphology was determined to be a process of nucleation and growth that could be controlled with a two-step sintering technique. The extent of texture was identified in the as-hot-pressed materials as a function of sintering conditions. Samples with different microstructures exhibited different hardness and fracture toughness. The true hardness was derived from the intrinsic relation between applied loads and indent sizes. The effect of microstructure on hardness and fracture toughness was analyzed. 相似文献
8.
Misha Zenotchkine Roman Shuba Joo Sun Kim I-Wei Chen 《Journal of the American Ceramic Society》2001,84(7):1651-1653
Single-phase seed crystals of Ca- and Y-α-SiAlONs have been synthesized for tailoring microstructure of α-SiAlON ceramics. The influence of composition, sintering temperature, and nitrogen pressure on the size and morphology of seeds has been explored. Guidelines for α-SiAlON seed preparation and morphology control are provided. 相似文献
9.
Zhijian Shen Hong Peng Pernilla Pettersson Mats Nygren 《Journal of the American Ceramic Society》2002,85(11):2876-2878
Alpha-SiAlON ceramics with a refined self-reinforced microstructure, i.e., containing acicular grains with dimensions much smaller than those obtained in previous studies, embedded in a matrix consisting of submicrometer-sized isotropic grains, were prepared by applying a rapid one-step sintering procedure. To suppress the overabundant formation of α-SiAlON nuclei, a combination of stabilizing cations, Y + Yb, was used; to encourage formation of acicular α-SiAlON grains, a small amount of an extra liquid (∼3 vol%) was introduced; to avoid abnormal grain coarsening resulting from dynamic ripening, the final sintering temperature was set to just slightly above the minimum temperature threshold for activating grain growth (1700°C). The fully dense compacts obtained exhibited excellent thermal-shock resistance, and hardness and fracture toughness values of 20 GPa and 5.1 MPa·m1/2 , respectively. 相似文献
10.
Katsutoshi Komeya Cheng Zhang Mikinori Hotta Junichi Tatami Takeshi Meguro Yi-Bing Cheng 《Journal of the American Ceramic Society》2000,83(4):995-997
Carbothermal reduction—nitridation (CRN) of SiO2 is an attractive method to manufacture Si3 N4 powders with controlled grain morphology. Moreover, β-SiAlON powders could also be synthesized from either pure powder mixture or some inexpensive raw minerals by CRN and the resulting powders favored the sintering of SiAlON product. However, there have been few works on preparing α-SiAlON powders so far. In this work, Ca α-SiAlON powder was synthesized by CRN of a SiO2 —Al2 O3 —CaCO3 mixture. An unusual morphology of hollow beads 200 to 500 nm in diameter with a great deal of nanosize α-SiAlON particles around 10 to 30 nm in diameter was observed from the resultant Ca α-SiAlON powders, which has not been reported for SiAlON ceramics before. 相似文献
11.
Ya-Wen Li Pei-Ling Wang Wei-Wu Chen Yi-Bing Cheng Dong-Sheng Yan 《Journal of the American Ceramic Society》2002,85(10):2545-2549
Two calcium-doped α-SiAlON compositions (Ca0.6 Si10.2 Al1.8− O0.6 N15.4 and Ca1.8 Si6.6 Al5.4 O1.8 N14.2 ) were prepared by hot pressing at 1600° and 1500°C, respectively, for complete phase transformation from α-Si3 N4 to α-SiAlON. Both samples were subsequently fired at different temperatures for different periods of time to study the grain growth of α-SiAlON. Elongated α-SiAlON grains were developed in both samples at high temperatures. The kinetics of grain growth was investigated based on the variations in length and width of the α-SiAlON grains under different sintering conditions. Different growth rates were found between the length and width directions of the α-SiAlON crystals, resulting in anisotropic grain growth in the microstructural development. 相似文献
12.
Chang-Meng Wang Mamoru Mitomo Fan-Fang Xu Naoto Hirosaki Yoshio Bando 《Journal of the American Ceramic Society》2001,84(6):1389-1391
Cerium α-SiAlON ceramics were made from a powder mixture of Si3 N4 -AlN-CeO2 that contained 1 wt% yttrium α-SiAlON powder. Plasma-activated sintering was used to examine the effect of the cooling rate on the formation of α-SiAlON. The formation of cerium α-SiAlON was suggested to be controlled by the nucleation at the surface of α-SiAlON nuclei, because α-phase formation could not occur without the addition of SiAlON powder. The solubility of cerium in the α-SiAlON was shown to be less than a previously predicted critical value. 相似文献
13.
Youichirou Kaga Mark I. Jones Kiyoshi Hirao Shuzo Kanzaki 《Journal of the American Ceramic Society》2004,87(5):956-959
A reaction-bonding process, which offers low sintering shrinkage and is a low-cost process, was applied to fabricate Y–α-SiAlON ceramics. The green compacts composed of Si, Y2 O3 , Al2 O3 , and AlN were nitrided and subsequently postsintered. Dense single-phase Y–α-SiAlON with elongated grain morphology could be achieved in the specimen postsintered at 1900°C. The material exhibited high hardness (1850 HV10) and high fracture toughness (5.1 MPa·m1/2 ). 相似文献
14.
Jiuxin Jiang Peiling Wang Wanbao He Weiwu Chen Hanrui Zhuang Yibing Cheng Dongsheng Yan 《Journal of the American Ceramic Society》2004,87(4):703-705
Self-propagating high-temperature synthesis (SHS) was applied to synthesize α-SiAlON powders doped by RE (RE = Eu,Pr,Ce) and codoped by RE and yttrium. The results showed that the weight ratio of α-SiAlON to (α-SiAlON +β-SiAlON) decreased from 70%, 55%, and 25% for europium-, praseodymium-, and cerium-doped α-SiAlON compositions, respectively, and the weight percentage of α-SiAlON phase increased to 100% for both (Eu,Y) and (Pr,Y) systems and 94% for the (Ce,Y) system, indicating SHS is a promising approach for synthesizing α-SiAlONs stabilized by the cations that could not be incorporated into the α-SiAlON structure by conventional sintering methods. 相似文献
15.
Z.-H. Xie M. Hoffman R. J. Moon P. R. Munroe Y.-B. Cheng 《Journal of the American Ceramic Society》2004,87(11):2114-2124
Two hot-pressed sintered α-sialon samples of differing microstructures, but identical chemical composition, were evaluated first, in terms of indentation hardness and modulus, by depth-sensing indentation (DSI) tests on planes parallel and normal to the hot-pressed surface. The surface and subsurface cracks created under the DSI tests have also been investigated in relation to the effect of microstructure. Subsequently, Vickers indentation tests were conducted to explore the deformation and fracture characteristics in the two samples. The effect of microstructure and grain orientation on the development of different types of cracks, in particular subsurface cracks, was revealed and analyzed. Additionally, it suggested that the focused ion beam (FIB) miller is a preferred tool, in comparison to the conventional cross-sectioning techniques, for examining subsurface crack formation and structural characteristics. 相似文献
16.
Single-phase in situ toughened SiAlON ceramics containing various modifying cations and single-crystal seeds were studied. The modifying cations include rare-earth cations from the smallest to the largest allowed in the α-SiAlON structure (Yb to Y, to Nd), and from monovalent to trivalent (Li to Ca, to rare earths). At low seeding levels, the aspect ratio of grains increases with the size of modifying cations, giving rise to rather different appearances of the microstructure in different SiAlONs. A one-to-one correspondence between seed crystals and large grains at low seeding levels is also observed. An optimal amount of seeds is required to maximize the fracture toughness, which is controlled by grain pullout with the fracture energy that scales with the fraction of elongated grains, their width, and their aspect ratio. The optimal amount of seeds required to reach maximal toughening increases with the aspect ratio of grains and is the lowest (1%) in Y- and Yb-SiAlONs. 相似文献
17.
采用熔融法制备了Eu掺杂的YAG微晶玻璃.通过XRD和FESEM,研究了纯相YAG晶体的析出和Eu掺杂前后YAG晶体的微结构变化,通过荧光光谱和CIE色坐标研究微晶玻璃的发光性能.结果表明:在1050℃热处理开始析出了纯相YAG晶体,晶粒尺寸20~60 nm.在短波和长波紫外光激发下都能同时得到Eu3+和Eu2+的特征发射峰,但长波紫外激发下的发光强度是短波激发下的数十倍.随着Eu掺杂浓度的增加,Eu2+发光强度明显增强, Eu3+发光强度先增强后降低.通过改变激发波长和Eu掺杂浓度,最后得到微晶玻璃样品的CIE色坐标为(0.3326, 0.3005),接近白光坐标.因此通过单掺杂Eu可以得到白光发光的YAG微晶玻璃. 相似文献
18.
19.
Mamoru Mitomo Yoh-ichiro Sato Nobuo Ayuzawa Isamu Yashima 《Journal of the American Ceramic Society》1991,74(4):856-858
Plasma etching of β-Si3 N4 , α-sialon/β-Si3 N4 and α-sialon ceramics were performed with hydrogen glow plasma at 600°C for 10 h. The preferential etching of β-Si3 N4 grains was observed. The etching rate of α-sialon grains and of the grain-boundary glassy phase was distinctly lower than that of β-Si3 N4 grains. The size, shape, and distribution of β-Si3 N4 grains in the α-sialon/β-Si3 N4 composite ceramics were revealed by the present method. 相似文献
20.
Feng Ye Michael J. Hoffmann Stefan Holzer Yu Zhou Mikio Iwasa 《Journal of the American Ceramic Society》2003,86(12):2136-2142
The yttrium–sialon ceramics with the composition of Y0.333 Si10 Al2 ON15 and an excess addition of Y2 O3 (2 or 5 wt%) were fabricated by hot isostatic press (HIP) sintering at 1800°C for 1 h. The resulting materials were subsequently heat-treated in the temperature range 1300–1900°C to investigate its effect on the α→β-sialon phase transformation, the morphology of α-sialon grains, and mechanical properties. The results show that α-sialons stabilized by yttrium have high thermal stability. An adjustment of the α-sialon phase composition is the dominating reaction in the investigated Y–α-sialon ceramics during low-temperature annealing. Incorporation of excess Y2 O3 could effectively promote the formation of elongated α-sialon grains during post-heat-treating at relatively higher temperature (1700° and 1900°C) and hence resulted in a high fracture toughness ( K IC = 6.3 MPa·m1/2 ) via grain debonding and pullout effects. Although the addition of 5 wt% Y2 O3 could promote the growth of elongated α grains with a higher aspect ratio, the higher liquid-phase content increased the interfacial bonding strength and therefore hindered interface debonding and crack deflection. The heat treatment at 1500°C significantly changed the morphology of α-sialon grains from elongated to equiaxed and hence decreased its toughness. 相似文献