Silicon nitride joining using rare-earth reaction sintering (original) (raw)
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Rapid fabrication of Si3N4 ceramics by reaction-bonding and pressureless sintering
Journal of the European Ceramic Society, 2016
Phase compositions, densification, microstructures, thermal conductivities, and mechanical properties of sintered reaction-bonded Si 3 N 4 (SRBSN) and sintered Si 3 N 4 (SSN) using the same additives and procedure were compared. The present results showed that the density of SRBSN with MgO-Y 2 O 3 additives was much lower than that of SSN with the same additives. The Eu 2 O 3-MgO-Y 2 O 3 additives inhibited the densification, while the ZrO 2-MgO-Y 2 O 3 additives promoted the densification. The SRBSN with relative density of 99.5% and thermal conductivity of 66.5 Wm −1 K −1 was rapidly prepared using ZrO 2-MgO-Y 2 O 3 as aids. The SSN with relative density of 99.0% and thermal conductivity of 56.8 Wm −1 K −1 was fabricated using ZrO 2-MgO-Y 2 O 3 additives. The comparable density and higher thermal conductivity made the SRBSN prepared rapidly from low cost Si starting powder superior over the SSN. This study suggested that the SRBSN route with a combination of nitridation catalyst and densification aids provided a promising route to fabricate cost-effective Si 3 N 4 ceramics.
Pressureless sintering of silicon nitride with additives of the Y2O3Al2O3SiO2 system
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1989
Pressureless sintering of Si3N 4 powder with 20 wt. % of mixed Y20~, Al203 and Si02 additives was carried out at 1650 °C under 1 atm flowing N 2 for 15-480 min. The a ~ fl phase transformation and densification kinetics during the first sintering stages seem to be controlled by the additive composition. Glassy grain boundary crystallization of as-sintered materials was performed at 1000 to 1300 °C producing yttrium aluminium garnet, ~03 "2Si02, Si2N:O and an unknown phase.
Ceramics International, 2019
The present paper reports the individual and combined effect of Y 2 O 3 and Al 2 O 3 as sintering additives during fabrication of Si 3 N 4-Mo-Si cermet by powder metallurgy route. Si 3 N 4 + Mo + Si cermet composition is prepared and different proportions of yttria (Y 2 O 3) and alumina (Al 2 O 3) are added to that composition as sintering additives. Powder mixture is cold compacted and finally sintered by conventional pressure-less sintering at 1500°C for 1hour in Argon gas atmosphere. The effect of the additives on the mechanical properties as well as microstructure of cermet has been investigated. Hardness and fracture toughness are found to be improved with combined addition of both the additives than that of individual addition. The maximum hardness and fracture toughness values are found in case of 5 wt. % Y 2 O 3 and 10 wt. % Al 2 O 3 added cermet with 11.41±0.43GPa and 7.005±0.58 MPa.m 1/2 respectively. However, the optimal results are found in case of 7.5 wt. % Y 2 O 3 and 7.5 wt. % Al 2 O 3 added cermet with relative density of 62.25%, micro-hardness of 8.07±0.55 GPa and fracture toughness of 4.57±0.44 MPa.m 1/2. From microscopic study it is observed that initial α-Si 3 N 4 transforms to β-Si 3 N 4 after sintering.
Journal of the Ceramic Society of Japan, 2006
SiO 2-MgO-Y 2 O 3 ¨ ʃï óďċí Ò ¶ W ¶ Thanakorn Wasanapiarnpong˩ ல ಓ şŁ ள ԇOEϥ_ _ (152-8550 ԇOE Aϥ 2-12-1 ಓ ùďēϥ_ӲѦ _ 10330 Ăí ÷ Si 3 N 4 ceramics were sintered at 1873-2023 K 1600-1750? C with additives from the SiO 2-MgO-Y 2 O 3 system. The degree of densification, a-b transformation, mass loss and microstructure were measured as a function of additives composition, sintering temperature, nitrogen gas pressure, and withwithout packing powder. Specimen prepared from 3 mass! SiO 2 , 3 mass! MgO, and 5 mass! Y 2 O 3 as the sintering additive could be sintered to almost full density at relatively low temperature as 1923 K for 2 h under ambient pressure of nitrogen atmosphere without using packing powder. The a-b transformation was not completed at this condition. The mass loss was relatively high due to the evaporation of SiO 2 and MgO. However, the resulted materials have high bending strength as 980 MPa, with fracture toughness of 6.6 MPaெm 12 , Vickers hardness of 18.4 GPa, and thermal conductivity of 34 Wm 1 K 1 .
Journal of Materials Science, 1995
=-sialon starting compositions with m = 1 and n = 1.7 have been densified by either hot-pressing or pressureless sintering using Y203 and Ln2Oa additions where Ln is neodymium, samarium, dysprosium or ytterbium. The resulting materials have been heat treated at 1450 ~ to crystallize the grain-boundary liquid into crystalline oxynitride phases. The effect of sintering additive on the design of final properties has been studied and Dy203 was found to be the best sintering additive to obtain desirable properties for ~-sialon and also =-13 sialon materials.
Materials Research, 2004
A comparative study was made of Si 3 N 4 sintered with two types of additives, namely, Y 2 O 3 /SiO 2 and R 2 O 3 (ss)/SiO 2 , R 2 O 3 (ss) being a rare earth metal oxide in solid solution. The processing conditions for both types of Si 3 N 4 were 14 vol% of additives and a sintering temperature of 1800 °C for 30, 60 and 240 min. To compare the efficiency of the additives in the material's sintering process, the density, flexural strength, fracture toughness and hardness were measured and the phase composition and microstructure determined. The results indicated that R 2 O 3 (ss)/SiO 2 as a sintering aid improved the material's high temperature strength and slowed down grain growth when compared with the Y 2 O 3 /SiO 2 additive.
Journal of Rare Earths, 2012
This paper presented the microstructure, mechanical properties and oxidation behavior of silicon nitride obtained by both conventional sintering and sintering followed by hot isostatic pressing (HIP). Silicon nitride with additives such as 5 wt.% Al 2 O 3 and 5 wt.% Ln 2 O 3 (Ln= La, La concentrate, Gd or La+Gd) were studied. The results revealed that Gd 2 O 3 additions increased the formation of elongated grains of ȕ-Si 3 N 4 , the fracture toughness and oxidation resistance. La 2 O 3 additions led to higher densification and hardness values, while addition of La 2 O 3 concentrate promoted the formation of materials with intermediate properties, compared to the other studied compositions. Hot isostatic pressing increased the hardness but decreased the fracture toughness of the material, mainly because it allowed residual pores to close and also reduced the average aspect ratio of ȕ-Si 3 N 4 grains.