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1.
The reaction sintering of β-sialon (Si4Al2O2N6) from a powder mixture of Si3N4, Al2O3 and AIN was studied to clarify factors affecting the densification. The presence of sufficient SiO vapour on the compact
and excess oxide with respect toβ-sialon composition was the most important factor. High densityβ-sialon was fabricated by heating the compact at 1800° C under 1 atm. N2. The sintering was carried out with sufficient SiO vapour pressure to prevent thermal decomposition of sintered sialon by
packing the compact with a powder mixture of Si3N4 and SiO2. Care was taken to minimize the amount of excess oxide in the starting composition to obtain a high density sialon with a
small amount of intergranular X-phase. The maximum density of 3.04 g cm−3 was obtained from the compact with 2 wt % excess Al2O3 in the composition. The strength of the sinteredβ-sialon was 490 MN m−2 at room temperature and 480 MN m−2 at 1200° C. The values are the best among those so far published for sinteredβ-sialons. 相似文献
2.
R. Larker L. -Y. Wei B. Loberg M. Olsson S. Johansson 《Journal of Materials Science》1994,29(16):4404-4414
Diffusion bonding by hot isostatic pressing (HIP) was performed between Incoloy 909 and five different ceramics. Two of the ceramics were composites made from powder mixtures of Si3N4 and either 60 vol% TiN or 50 vol% TiB2, while three were monolithic materials, namely Si3N4 with 2.5 wt% Y2O3 as a sintering additive, Si3N4 without additives, and Si2 N2O without additives. A diffusion couple geometry was developed to facilitate the preparation of thin-foil specimens for examination by analytical electron microscopy (AEM). Diffusion bonding was performed by HIP at 927°C (1200K) and 200 MPa for 4 h. The formation of reaction layers was very limited, being less than 1 m in total layer thickness. Two reaction products were found by AEM; a continuous, very thin, (100 nm) layer of fine TiN crystals at the initial ceramic/metal interface, and larger grains extending about 100–500 nm into the superalloy and forming a semi-continuous layer of a G-phase suicide containing mainly nickel, silicon and niobium. 相似文献
3.
Bošković S. Sigulinski F. Živković Lj. 《Journal of Materials Synthesis and Processing》1999,7(2):119-126
Densification during liquid-phase sintering of Si3N4–TiN was studied in the presence of Y2O3. The content of TiN was varied from 0–50 mass%. During the densification Y-silicate was formed. The amount of silicate increased with both decreasing fraction of TiN and increasing isothermal heating time. Density, fracture toughness, and electrical resistivity were measured as a function of TiN content. It was found that the density and fracture toughness increased with increasing TiN content. The electrical resistivity drops drastically, from 1010 m for sintered Si3N4 to 10–3 m for sintered Si3N4–TiN composite containing 30 vol% TiN. 相似文献
4.
Z. Y. Ma J. H. Li S. X. Li X. G. Ning Y. X. Lu J. Bi 《Journal of Materials Science》1996,31(3):741-747
The in situ formed Al2O3, TiB2 and Al3Ti mixture-reinforced aluminium composites were successfully fabricated by the reaction sintering of the TiO2-B-Al system in a vacuum. With increasing boron content in the TiO2-B-Al system, the amount of generated TiB2 in the composites increased and Al3Ti content decreased. At the same time the distribution uniformity of the in situ formed Al2O3 and TiB2 particulates was obviously improved, and the size of the Al3Ti particles was reduced. The in situ Al2O3 and TiB2 particulates had sizes from 0.096–1.88 m. The interface between the in situ formed particulates and the aluminium matrix was clean, and no consistent crystallographic orientation relationship was found. The strength and elastic modulus of the composites was significantly improved by lowering the Al3Ti content. When the boron content in the TiO2-B-Al system rose, the morphology of the tensile fracture surface of the composites was changed from large fractured Al3Ti blocks and fine dimples, to fine dimples and pulled-out particulates. The strengthening and fracture of the composites have been modelled. 相似文献
5.
Jow -Lay Huang Ming -Tung Lee Horng -Hwa Lu Ding -Fwu Lii 《Journal of Materials Science》1996,31(18):4899-4906
Silicon nitride containing various compositions of as-received TiC and TiN-coated TiC, were hot pressed at 1800 °C for 1 h in a nitrogen atmosphere. In TiN-coated TiC/Si3N4 composites, TiC reacted first with the TiN coating to form a titanium carbonitride interlayer at 1450 °C, which essentially reduced further reactions between TiC and Si3N4 and enhanced densification. TiN-coated TiC/Si3N4 composites exhibited better densification, hardness, flexural strength and fracture toughness than those of as-received TiC/Si3N4. The toughening mechanisms for as-received TiC/Si3N4 and TiN-coated TiC/Si3N4 composite were attributed to crack deflection, load transfer and crack impedence by the compressive thermal residual stress. 相似文献
6.
Kyeong -Sik Cho Young -Wook Kim Heon -Jin Choi June -Gunn Lee 《Journal of Materials Science》1996,31(23):6223-6228
Particle-reinforced SiC composites with the addition of TiC or TiB2 were fabricated at 1850 °C by hot-pressing. Densification was accomplished by utilizing a liquid phase formed with added Al2O3, Y2O3, and surface SiO2 on SiC. Their mechanical and electrical properties were measured as a function of TiC or TiB2 content. Adding TiC or TiB2 to the SiC matrix increased the toughness, and decreased the strength and electrical resistivity. The fracture toughnesses of SiC-50 wt% TiC and SiC-50 wt% TiB2 composites were approximately 60% and 50%, respectively, higher than that of monolithic SiC ceramics. Microstructural analysis showed that the toughening was due to crack deflection, with some possible contribution from microcracking in the vicinity of TiC or TiB2 particles. 相似文献
7.
N. Zhilinska I. Zalite J. Grabis G. Kladler 《Materialwissenschaft und Werkstofftechnik》2003,34(4):327-331
Si3N4‐Al2O3‐Y2O3, Si3N4‐TiN and Si3N4‐AIN‐Al2O3‐Y2O3 (β‐sialon) nanopowders with the specific surface area of 60–70 m2/g and average particle size of 30–50 nm have been prepared by plasmachemical synthesis. By means of the hot pressing method at 1850°C compact materials with fine‐grained structure were prepared from this powders as well as from mixture of Si3N4‐Al2O3‐Y2O3 with the second phase (10 wt.% SiC‐Si3N4, ZrO2, TiN nanopowder). Addition of the second phase to silicon nitride improves material strength. 相似文献
8.
Shih-Cheng Chuang Cheng-Tzu Kuo Chi-Ting Ho Al-Kang Li 《Journal of Materials Science》1992,27(22):6213-6218
In situ formation of TiB2 in Al2O3 matrix through the reaction of TiO2, boron and carbon has been studied. In hot-pressed samples, in addition to TiB2, TiC and Al2TiO5 were also found to be dispersed phases in Al2O3 matrix. However, in the case of pressureless-sintered samples, pure Al2O3/TiB2 composite with > 99% relative density can be obtained through a preheating step held at 1300°C for longer than 30 min and then sintering at a temperature above 1500°C. Pressureless-sintered composite containing 20vol% TiB2 gives a flexural strength of 580 MPa and a fracture toughness of 7.2 MPa m1/2. 相似文献
9.
A sialon composite composed of Y-α′-sialon and β′-sialon has been fabricated by hot pressing mixtures of Si3N4, Y2O3 and AlN powders. Thermal expansion coefficients of the Y-α′-sialon and β′-sialon were determined by the high-temperature
X-ray diffraction technique. The thermal expansion coefficient of Y-α′-sialon depended on the composition, being minimum at
x=0.3 in the formula Yx(Si12-4.5x, Al4.5x)(O1.5x, N16-1.5x). The coefficient of β′-sialon increased with increasing lattice constant, that is, the z value in the formula Si6-zAlzOzN8-z. The thermal expansion coefficient of sialon composites determined by a differential dilatometer increased with increasing
amount of Y-α′-sialon.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
10.
A powder mixture of ultrafine –SiC–35 wt% –Si3N4 containing 6 wt% Al2O3 and 4 wt% Y2O3 as sintering additives were liquid–phase sintered at 1800°C for 30 min by hot–pressing. The hot–pressed composites were subsequently annealed at 1920°C under nitrogen–gas–pressure to enhance grain growth. The average grain–size of the sintered bodies were ranged from 96 to 251 nm for SiC and from 202 to 407 nm for Si3N4, which were much finer than those of ordinary sintered SiC–Si3N4 composites. Both strength and fracture toughness of fine–grained SiC–Si3N4 composites increased with increasing grain size. Such results suggested that a small amount of grain growth in the fine–grained region (250 nm for SiC and 400 nm for Si3N4) was beneficial for mechanical properties of the composites. The room–temperature flexural strength and fracture toughness of the 8–h annealed composites were 698 MPa and 4.7 MPa · m1/2, respectively. 相似文献
11.
Reactive hot-press (1800-1880 °C, 30 MPa, vacuum) is used to fabricate relatively dense B4C matrix light composites with the sintering additive of (Al2O3 +Y2O3). Phase composition, microstructure and mechanical properties are determined by methods of XRD, SEM and SENB, etc. These results show that reactions among original powders B4C, Si3N4 and TiC occur during sintering and new phases as SiC, TiB2 and BN are produced. The sandwich SiC and claviform TiB2 play an important role in improving the properties. The composites are ultimately and compactly sintered owing to higher temperature, fine grains and liquid phase sintering, with the highest relative density of 95.6%. The composite sintered at 1880 °C possesses the best general properties with bending strength of 540 MPa and fracture toughness of 5.6 MPa m1/2, 29 and 80% higher than that of monolithic B4C, respectively. The fracture mode is the combination of transgranular fracture and intergranular fracture. The toughening mechanism is certified to consist of crack deflection, crack bridging and pulling-out effects of the grains. 相似文献
12.
Si3N4-ZrO2 composites have been prepared by hot isostatic pressing at 1550 and 1750 °C, using both unstabilized ZrO2 and ZrO2 stabilized with 3 mol% Y2O3. The composites were formed with a zirconia addition of 0, 5, 10, 15 and 20 wt%, with respect to the silicon nitride, together with 0–4 wt% Al2O3 and 0–6 wt% Y2O3. Composites prepared at 1550 °C contained substantial amounts of unreacted -Si3N4, and full density was achieved only when 1 wt% Al2O3 or 4 wt % Y2O3 had been added. These materials were generally harder and more brittle than those densified at the higher temperature. When the ZrO2 starting powder was stabilized by Y2O3, fully dense Si3N4-ZrO2 composites could be prepared at 1750 °C even without other oxide additives. Densification at 1750 °C resulted in the highest fracture toughness values. Several groups of materials densified at 1750 °C showed a good combination of Vickers hardness (HV10) and indentation fracture toughness; around 1450 kg mm–2 and 4.5 MPam1/2, respectively. Examples of such materials were either Si3N4 formed with an addition of 2–6 wt% Y2O3 or Si3N4-ZrO2 composites with a simultaneous addition of 2–6 wt%Y2O3 and 2–4 wt% Al2O3. 相似文献
13.
Mechanical properties of Al2O3 particle-Y-TZP matrix composite and its toughening mechanism 总被引:6,自引:0,他引:6
Dense Al2O3 particle-Y-TZP matrix (Al2O3<40 vol%) composite was prepared by pressureless sintering at 1550°C. Composites with 10–30 vol% Al2O3 particles showed enhanced fracture toughness, bending strength and Vicker's hardness as compared to single-phase Y-TZP. The highest strength (1150 MPa) and highest toughness (12.4 MPa m1/2) were obtained for the composite containing 10 vol% Al2O3. It was found that, in addition to the contribution by the crack-deflection effect, the enhanced phase transformation from tetragonal to monoclinic during fracture was the main toughening mechanism in operation in the composites. 相似文献
14.
Effect of cutting speed on the performance of Al2O3 based ceramic tools in turning nodular cast iron 总被引:1,自引:0,他引:1
N. Camucu 《Materials & Design》2006,27(10):997-1006
This paper presents the results of an experimental investigation on the effect of cutting speed in turning nodular cast iron with alumina (Al2O3) based ceramic tools. Three different alumina based ceramic cutting tools were used, namely TiN coated Al2O3 + TiCN mixed ceramic, SiC whisker reinforced Al2O3 and uncoated Al2O3 + TiCN mixed ceramic tool. Turning experiments were carried out at four different cutting speeds, which were 300, 450, 600 and 750 m/min. Depth of cut and feed rate were kept constant at 1 mm and 0.1 mm/rev, respectively, throughout the experiments. Tool performance was evaluated with respect to tool wear, surface finish produced and cutting forces generated during turning. Uncoated Al2O3 + TiCN mixed ceramic was the worst performing tool with respect to tool wear and was the best with respect to surface finish. SiC whisker reinforced Al2O3 exhibited the worst performance with respect to cutting forces. If tool wear, surface finish and cutting force results are considered together, among the three tools studied, TiN coated Al2O3 + TiCN mixed ceramic tool is the most suitable one for turning nodular cast iron, especially at high cutting speeds (Vc > 600 m/min). 相似文献
15.
The crystallisation of M-SiAlON glasses (M = Y, Ln) is particularly sensitive to small variations in composition and heat treatment temperature. The formation of Iw-phase in the YSiAlON system has been studied but little information concerning its nucleation, thermal stability, mechanical properties and extension into the lanthanide sialon series is available. In order to better understand the synthesis and to characterise more fully the Iw-glass-ceramic materials, a series of glass compositions have been prepared and characterised. These include M3Si3Al2O12.15N0.90 (M = Y, Er, Ce, Yb); M3.45Si3Al2O12.76N0.95 (M = Y, Er); Y4Si3Al2O13.50N and Y4Si3.37Al1.50O13.50N. Heat treatments were performed on these glasses and the resulting crystalline products have been studied by X-ray diffraction (XRD). Differential Thermal Analysis (DTA) in combination with XRD analysis of Y3.45Si3Al2O12.76N0.95 and Ce3Si2Al2O12.15N0.90 parent glass-compositions was used to investigate crystal phase formation. Young's modulus (E), hardness (H
v and fracture toughness (K
IC) of the glass-ceramics were measured. Glass-ceramics containing Iw-phase as the only detectable crystalline phase have been produced from M3Si3Al2O12.15N0.90 and M3.45Si3Al2O12.76N0.95 (M = Y and Er) compositions. No equivalent phase was found in the Ce- and Yb-sialon compositions. 相似文献
16.
Si3N4 Ceramic Composites with TiC powder have been fabricated by gas-pressure sintering and their electrical conductivity has been investigated. The ceramic composites with different electrical resistivity consist of Si3N4 powder as an insulating matrix, and TiC as electrically conductive additive. Under tensile loading or compressive unloading, the R/R of TiC/Si3N4 composites reversibly increased. Under compressive loading, the R/R decreased gradually with the increasing of loading up to fracture. The results suggest the possibility of self-monitoring fractures and strains in the composites under tensile and compressive loading. 相似文献
17.
G. D. Quinn 《Journal of Materials Science》1987,22(1):374-380
The static fatigue and creep resistances of a commercial sialon material were evaluated by elevated temperature flexural stress rupture testing in air. The material is a ceramic alloy with a solid solution sialon phase, Si6-z
Al
z
O
z
N8-z
, with a substitution levelz less than 1. The utilization of yttria sintering aids and post-sintering heat treatments leads to a fully crystalline grain-boundary phase. Creep and static fatigue resistances were excellent at temperatures up to 1200° C. 相似文献
18.
TiC/TiN+TiCN reinforced composite coatings were fabricated on Ti?C6Al?C4V alloy by laser cladding, which improved surface performance of the substrate. Nano-CeO2 was able to suppress crystallization and growth of the crystals in the laser-cladded coating to a certain extent. With the addition of proper content of nano-CeO2, this coating exhibited fine microstructure. In this study, the Al3Ti+TiC/TiN+nano-CeO2 laser-cladded coatings were studied by means of X-ray diffraction and scanning electron microscope. The X-ray diffraction results indicated that the Al3Ti+TiC/TiN+nano-CeO2 laser-cladded coating consisted of Ti3Al, TiC, TiN, Ti2Al20Ce, TiC0·3N0·7, Ce(CN)3 and CeO2, this phase constituent was beneficial to increase the microhardness and wear resistance of Ti?C6Al?C6V alloy. 相似文献
19.
Hot-pressed Si3N4, sintered Si3N4 and three kinds of sialon with different compositions were oxidized in dry air and wet nitrogen gas atmospheres at 1100 to 1350° C and 1.5 to 20 kPa water vapour pressure. All samples were oxidized by both dry air and water vapour at high temperature, and formed oxide films consisting of SiO2, Y2Si2O7 and Y4A1209. The oxidation rate was in the order sialon > sintered Si3N4 > hot-pressed Si3N4. The oxidation rate of sialon increased with increasing Y2O3 content, and oxidation kinetics obeyed the usual parabolic law. The oxidation rates in dry air and wet nitrogen were almost the same: the rate in wet nitrogen was unaffected by water vapour pressure above 1.5 kPa. The activation energy was about 800 kJ mol–1. 相似文献
20.
Joon -Hong Kim Tae -Sung Oh Mee -Sook Lee Jae -Gwan Park Yoon -Ho Kim 《Journal of Materials Science》1993,28(6):1573-1577
The effects Al2O3 doping on the sintering behaviour and ionic conductivity of nasicon have been investigated using formulations of Na3+2x
Zr2Si2Al
x
P1–x
O12 where Al3+ ions were substituted to P5+ sites within the range 0x0.2. The density of Na3+2x
Zr2Si2Al
x
P1–x
O12 was increased with increasing amount of Al2O3 doping due to the enhanced liquid-phase sintering. The relative density of Na3.4Zr2Si2Al0.2P0.8O12 reached a maximum value of 96% when sintered at 1200°C for more than 7 h. The maximum conductivity of 0.24 –1 cm–1 at 300°C was obtained for the composition with x=0.1 when sintered at 1200°C for 10 h. 相似文献