共查询到20条相似文献,搜索用时 31 毫秒
1.
Jae-Yeon Kim Young-Wook Kim June-Gunn Lee Kyeong-Sik Cho 《Journal of Materials Science》1999,34(10):2325-2330
Alpha-SIC powder containing 7.2 wt % Y3Al5O12 (YAG, yttrium aluminum garnet) and 4.8 wt % SiO2 as sintering aids were hot-pressed (SC0) at 1820°C for 1 h and subsequently annealed at 1920°C for 2 h (SC2), 4 h (SC4) and 8 h (SC8). When the annealing time was increased, the microstructure changed from equiaxed to elongated grains and resulted in self-reinforced microstructure consisted of large elongated grains and small equiaxed grains. Development of self-reinforced microstructure, consisted of mostly 6H phase, resulted in significant improvements in toughness. However, the improved toughness was offset by a significant reduction in strength as in the materials consisted of 4H originated from -SiC. The fracture toughness and strength of the 8-h annealed materials were 5.5MPa · m1/2 and 490 MPa, respectively. 相似文献
2.
Si3N4-SiC composites have been microwave sintered using β-Si3N4 and β-SiC as starting materials. Si3N4 rich compositions (95 and 90 vol.% Si3N4) have been sintered above 96% of theoretical density without using any sintering additives in 40 min. A monotonic decrease
in relative density is observed with increase in SiC proportion in the composite. Decrease in relative density has manifested
in the reduction of fracture toughness and microhardness values of the composite with increase in SiC content although the
good sintering of matrix Si3N4 limits the decrease of fracture toughness. Highest value of fracture toughness of 6.1 MPa m1/2 is observed in 10 vol.% SiC composite. Crack propagation appears to be transgranular in the Si3N4 matrix and the toughening of the composites is through crack deflection around hard SiC particles in addition to its debonding
from the matrix. 相似文献
3.
D. Bučevac S. Bošković B. Matović Lj. Živković M. Vlajić Vladimir Krstić 《Journal of Materials Science》2007,42(18):7920-7926
Microstructure development and fracture toughness of Si3N4 composites were studied in the presence of seeds and Al2O3 + Y2O3 as sintering aids. The elongated β-Si3N4 seeds were introduced into two different α-Si3N4 matrix powders; one was the ultra fine powder matrix and the other was the coarse powder matrix. The amount of seeds varied
from 0 to 6 wt%. The grain growth inhibition and the mechanism of toughening were discussed and correlated with microstructure.
The maximum fracture toughness of 9.0 MPa m1/2 was obtained for ultra fine powder with 5 wt% seeds hot pressed at 1,700 °C for 6 h. 相似文献
4.
The effect of seeding on microstructural development and fracture toughness of -SiC with an oxynitride glass was investigated by the use of morphologically rodlike -SiC whiskers. A self reinforced microstructure consisting of rodlike -SiC grains and equiaxed -SiC matrix grains was obtained by seeding 1–10 wt% SiC whiskers, owing to the epitaxial growth of -SiC from the seed whiskers. Further addition of seeds (20 wt%) or further annealing at higher temperatures led to a unimodal microstructure, owing to the impingement of growing seed grains. By seeding -SiC whiskers, fracture toughness of fine-grained materials was improved from 2.8 to 3.9–6.7 MPa · m1/2, depending on the seed content. 相似文献
5.
Kyeong-Sik Cho Heon-Jin Choi June-Gunn Lee Young-Wook Kim 《Journal of Materials Science》1998,33(1):211-214
A process based on liquid phase sintering and subsequent annealing for grain growth is presented to obtain the in situ enhancement of toughness of SiC–30 wt%, 50 wt%, and 70 wt% TiB2 composites. Its microstructures consist of uniformly distributed elongated -SiC grains, relatively equiaxed TiB2 grains, and yttrium aluminium garnet (YAG) as a grain boundary phase. The composites were fabricated from -SiC and TiB2 powders with the liquid forming additives of Al2O3 and Y2O3 by hot-pressing at 1850°C and subsequent annealing at 1950°C. The annealing led to the in situ growth of elongated -SiC grains, due to the phase transformation of SiC, and the coarsening of TiB2 grains. The fracture toughness of the SiC–50 wt% TiB2 composites after 6 h annealing was 7.3 MPa m1/2, approximately 60% higher than that of as-hot-pressed composites (4.5 MPa m1/2). Bridging and crack deflection by the elongated -SiC grains and coarse TiB2 grains appear to account for the increased toughness of the composites. 相似文献
6.
Pengfei Zhang Dechang Jia Zhihua Yang Xiaoming Duan Yu Zhou 《Journal of Materials Science》2012,47(20):7291-7304
The mechanically alloyed amorphous SiBCN powders were hot pressed at 1500, 1600, 1700, 1800, and 1900 °C under a pressure of 80 MPa in the nitrogen atmosphere for 30 min. The crystallization, the microstructural evolution, and the properties of the prepared ceramics were carefully studied by XRD, TEM, HRTEM, and property testing. Results show that the crystallization of β-SiC, turbostratic BN(C), and α-SiC in the amorphous matrix starts at about 1500, 1600, and 1700 °C, respectively. When the powder is hot pressed at the temperatures higher than 1700 °C, the prepared ceramics always consist of nano β-SiC, α-SiC, turbostratic BN(C), and amorphous body. With the increase of the sintering temperature, the ceramic crystallinity becomes higher, the grains get larger, and the amorphous content becomes lower. At the temperatures lower than 1800 °C, the bulk density, the relative density, the flexural strength, the Young’s modulus, and the fracture toughness of the prepared ceramics show persistent but insignificant increase. However, when the ceramic is sintered at 1,900 °C, these properties are rapidly improving to 2.6 g/cm3, 91.8 %, 331.0 MPa, 139.4 GPa, and 2.8 MPa m1/2. 相似文献
7.
Composites of SiC-TiC containing up to 45 wt% of dispersed TiC particles were pressureless sintered to 97% of theoretical density at temperatures between 1850°C and 1950°C with Al2O3 and Y2O3 additions. An in situ-toughened microstructure, consisted of uniformly distributed elongated -SiC grains, matrixlike TiC grains, and yttrium aluminum garnet (YAG) as a grain boundary phase, was developed via pressureless sintering route in the composites sintered at 1900°C. The fracture toughness of SiC-30 wt% TiC composites sintered at 1900°C for 2 h was as high as 7.8 MPa·m1/2, owing to the bridging and crack deflection by the elongated -SiC grains. 相似文献
8.
By adjusting the : SiC phase ratios in the individual starting powders, a layered SiC consisting of surface and inner layers with distinctively different microstructures are produced by hot-pressing and subsequent annealing. The surface layer consisted of relatively fine, equiaxed -SiC grains, designed for high strength, while the inner layer consisted of elongated -SiC grains, designed for high toughness. By virtue of the common SiC phase and the same sintering aids (Al2O3-Y2O3), the interlayer interfaces are chemically compatible and strongly bonded. R-curve behavior of the layered SiC was measured and compared with the related monolithic materials. The layered SiC showed better damage tolerance than monolithic materials and stronger R-curve behavior than surface layer. This superior performance of layered SiC ceramics was attributed to the contribution of both high strength of the surface layer for small flaws and high toughness of the inner layer for larger flaws. 相似文献
9.
Hai-Long Wang Chang-An Wang De-Liang Chen Hong-Ling Xu Hong-Xia Lu Rui Zhang Lun Feng 《Frontiers of Materials Science in China》2010,4(3):276-280
ZrB2-SiC ultra-high temperature ceramic composites reinforced by nano-SiC whiskers and SiC particles were prepared by microwave
sintering at 1850°C. XRD and SEM techniques were used to characterize the sintered samples. It was found that microwave sintering
can promote the densification of the composites at lower temperatures. The addition of SiC also improved the densification
of ZrB2-SiC composites and almost fully dense ZrB2-SiC composites were obtained when the amount of SiC increased up to 30vol.%. Flexural strength and fracture toughness of
the ZrB2-SiC composites were also enhanced; the maximum strength and toughness reached 625 MPa and 7.18 MPa·m1/2, respectively. 相似文献
10.
Hai-Long Wang Chang-An Wang De-Liang Chen Hong-Ling Xu Hong-Xia Lu Rui Zhang Lun Feng 《材料科学前沿(英文版)》2010,4(3):276-280
ZrB2-SiC ultra-high temperature ceramic composites reinforced by nano-SiC whiskers and SiC particles were prepared by microwave sintering at 1850°C. XRD and SEM techniques were used to characterize the sintered samples. It was found that microwave sintering can promote the densification of the composites at lower temperatures. The addition of SiC also improved the densification of ZrB2-SiC composites and almost fully dense ZrB2-SiC composites were obtained when the amount of SiC increased up to 30vol.%. Flexural strength and fracture toughness of the ZrB2-SiC composites were also enhanced; the maximum strength and toughness reached 625 MPa and 7.18 MPa·m1/2, respectively. 相似文献
11.
Bo Wang Jun Yang Rui Guo Jiqiang Gao Jianfeng Yang 《Journal of Materials Science》2009,44(5):1351-1356
Si3N4-barium aluminum silicate (BAS) self-reinforced composites have been prepared by pressureless sintering at 1800 °C for 2 h.
The β-Si3N4 seeds incorporated in the starting α-Si3N4 powders encouraged the α- to β-Si3N4 phase transformation, and the final bimodal microstructure with large grains, consequently, led to the improvement of the
fracture toughness, from 7.74 to 8.34 MPa m1/2. The almost-complete crystallized BAS benefited the high-temperature mechanical properties. The residual stress, crack deflection,
grain bridging, and pullout were considered as the major toughening mechanisms in this composite. 相似文献
12.
In situ synthesis of Mo(Si,Al)2-SiC composites 总被引:1,自引:0,他引:1
An in situ reaction was proposed and investigated to produce Mo(Si1 – x
Al
x
)2-SiC composites. The starting powders were MoSi2, Al and C. A direct current hot pressing (DCHP) method was used to prepare these composites. When the mixed powder was hot pressed at temperatures lower than 1500°C, the phase composition was Mo(Si,Al)2 and -SiC. When the hot pressing temperature was higher than 1600°C, however, Nowotny phase Mo5Si3C1 appeared. The chemical stoichiometry of the proposed in situ reaction becomes difficult because of the formation of solid solution among these phases and the appearance of Mo5Si3C phase. The in situ formed SiC phase in the x = 0.3 sample was partly in whisker shape. However, the SiC phase in x = 0.15 sample was in particle shape. These in situ formed SiC particles and whiskers acted as crack deflection and bridging elements and improved the fracture toughness. The Vickers hardness and fracture toughness of the x = 0.3 sample hot pressed at 1700°C for 60 min in vacuum were 15.6 GPa and 5.39 MPa · m1/2, respectively. 相似文献
13.
14.
Young-Il Lee Young-Wook Kim Heon-Jin Choi June-Gunn Lee 《Journal of Materials Science》2001,36(3):699-702
Powder mixtures of -SiC--Si3N4 in a weight ratio of 1 : 1 containing 5–20 wt% Y-Mg-Si-Al-O-N oxynitride as a sintering additive were liquid-phase sintered at 1800°C for 3 h by hot-pressing. These materials had a microstructure of in situ-toughened composites as a result of the phase transformation of Si3N4 during sintering. The introduction of larger amount of additives accelerated the grain growth of elongated -Si3N4 grains with higher aspect ratio, resulting in the improved fracture toughness and strength. Typical flexural strength and fracture toughness of SiC-Si3N4 composites containing 15 wt% oxynitride glass were 860 MPa and 5.7 MPa · m1/2, respectively. 相似文献
15.
Additions of AlN and Al2O3 to -SiC hot pressed at 2100°C strongly effect the - to -SiC phase transformation and the resultant -SiC polytypes which are formed. Scanning and transmission electron microscopy were utilized to investigate the microstructural changes occurring in SiC due to these additions and to correlate these observations to their mechanical properties. The results suggest that Al2O3 additions stabilize the formation of the 6H-polytype of -SiC which grows rapidly into an elongated plate-like morphology, while AlN additions stabilize the 2H-polytype of -SiC resulting in fine equiaxed 2H-SiC: AlN solid solution grains. It is speculated that the elongated growth of 6H-SiC with Al2O3 additions can be controlled through the simultaneous addition of AlN. The formation of 2H-SiC : AlN solid solution grains inhibits the growth of the 6H-SiC grains since AlN(2H) will not go into solid solution in the SiC(6H) structure, effectively pinning the growth of the 6H-SiC grains. 相似文献
16.
KMg2AlSi4O12 is a phyllosiloxide isostructural with phlogopite mica, but totally free of OH- ions. It decomposes at ≈ 950 °C at atmospheric pressure but remains stable up to at least 1350 °C under high pressures. Its
chemical compatibility with α-alumina, MgAl2O4 spinel, forsterite, β-SiC and borosilicate glass selected as representative of fibres and matrices in ceramic matrix composites
(CMCs), has been assessed via annealing experiments on multilayers and particulate composites at 900–1200 °C. At T = 900 °C and P = 100 MPa, the phyllosiloxide is chemically stable with respect to all the ceramics. At higher temperatures, interdiffusion
occurs with the formation of various reaction products. At T = 1050 °C and P = 2 GPa, the extent of the reaction zone is larger for both α-alumina and forsterite than for spinel and β-SiC, whereas at
1200 °C, the reactivity of the phyllosiloxide with all the ceramics becomes about the same. Borosilicate glass with a softening
point lower than the decomposition onset of KMg2AlSi4O12 at relatively low pressures seems to be an ideal model matrix material for assessing the potential of the phyllosiloxide
as an interphase material in CMCs.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
17.
High-density BAS/SiC composites were obtained from β-SiC starting powder by the spark plasma sintering technique. Various physical properties of the BAS/SiC composites were investigated in detail, such as densification, phase analysis, microstructures and mechanical properties. The results demonstrated that the relative density of the BAS/SiC composites reached over 99.4% at 1900 °C. The SiC grains were uniformly distributed in the continuous BAS matrix which is probably because of complete infiltration of the SiC particles in BAS liquid-phase formed during sintering. The pull-out of SiC particles, crack deflection and bridging were observed as the major toughening mechanism. The flexural strength and fracture toughness of the BAS/SiC composites sintered at 1900 °C were up to 560 MPa and 7.0 MPa·m1/2, respectively. 相似文献
18.
Youichirou Kaga Mark I. Jones Kiyoshi Hirao Shuzo Kanzaki 《Journal of Materials Science》2007,42(2):699-704
Y-α-SiAlONs with elongated grains were fabricated via a reaction-bonding process using starting compositions containing excess
oxides in the form of Y2O3 and SiO2. The density of post-sintered specimens reached a maximum value with compositions containing 2 mass% excess oxides, although
conventionally sintered materials of this composition were not fully dense. However for compositions containing smaller amounts
of excess oxides, the density of the specimen fabricated via a reaction-bonding process was lower than that via a conventional
process. In these samples it is thought that liquid phase sintering was difficult to be achieve during the post-sintering
process, since the amount of SiO2 contained in the starting powder was lower and the Al2O3 in the starting composition was consumed for the production of β-SiAlON during nitridation. There was also a decrease in
density of the reaction-bonded materials with further increases in the amounts of additional oxides. For these samples the
compacts could not be densified uniformly, because of non-uniformity of the phase composition in the nitrided compacts. The
dense reaction bonded α-SiAlON with elongated grains, fabricated from compositions with 2 mass% excess oxides exhibited both
high fracture toughness and high hardness. 相似文献
19.
Dense ceramics with overall compositions DyxSi12-4.5xAl4.5xO1.5xN16-1.5x, where 0.2≤x≤1.0, along the Si3N4–Dy2O3·9AlN tie
line were prepared by hot-pressing at 1800°C. The dysprosium-doped α-sialon phase formed in the composition range 0.3≤x≤0.7.
Sintered materials of different compositions were post-heat-treated at temperatures in the range 1300–1750° C for different
times and it was shown that the Dy-α-sialon phase is stable over a large temperature interval and during heat treatment times
up to 30 days. Unlike corresponding neodymium- and samarium-doped α-sialons, dysprosium-doped α-sialon does not decompose
into β-sialon and rare-earth-rich grain-boundary phase(s) at temperatures below 1550°C. The α-phase can coexist with a liquid
phase at temperatures ≥1550°C and with the Dy-M′-phase (Dy2Si3-xAlxO3+xN4-x) at lower temperatures. When heat treated at 1450°C,
any residual liquid grain-boundary phase reacted with minor amounts of the α-sialon phase and devitrified to Dy-M′-phase,
yielding a glassy phase-free material. The Dy-M′-phase formed had the maximum aluminium substitution, i.e. x≈0.7. Dysprosium-doped
α-sialon exhibited very high hardness (Hv10=22 GPa) and a fracture toughness of 4.5 MPa m1/2, and the hardness and toughness
decreased only slightly after devitrification of the glassy phase. Some elongated α-sialon grains were formed at high x values
in glassy phase-containing materials, but their presence did not affect the toughness significantly.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
20.
A powder compact of α-SiC and α-Al2O3 was infiltrated with a liquid precursor of SiO2, which on subsequent heat treatment at 1500 °C produced a mullite bonded porous SiC ceramics. Results showed that infiltration
rate could be estimated by using weight gain measurements and theoretical analysis. The bond phase was composed of needle-shaped
mullite which was observed to be grown from a siliceous melt formed during the process of oxide bonding. The porous SiC ceramics
exhibited a density and porosity of 2 g cm−3 and 30 vol%, respectively, and also a pore size distribution in a range of 2–15 μm with an average pore size of 5 μm. No
appreciable degradation of room temperature flexural strength (51 MPa) was observed at high temperatures (1100 °C). 相似文献