Liquid phase sintering of silicon carbide with AlN/Y2O3, Al2O3/Y2O3 and SiO2/Y2O3 additions

Abstract

In this work, the influence of the additive system on the liquid phase sintering of silicon carbide has been investigated. The additives employed were mixtures of AlN/Y2O3, Al2O3/Y2O3 and SiO2/Y2O3. The total additive content was fixed at 20 vol.-%, maintaining the Y2O3 content in each additive system at 35 vol.-%. Cold isostatically pressed samples were sintered at 1900, 2000 and 2100 °C under Ar atmosphere during 30min. The most promising results have been obtained by samples with AlN/Y2O3 additions sintered at 2000 °C, exhibiting the smallest weight loss of about 6% and the highest flexural strengths of about 433 MPa. Samples with Al2O3/Y2O3 and SiO2/Y2O3 additions exhibited high weight loss, because of reactions of Al2O3 and SiO2 with the SiC matrix, forming gaseous species such as Al2O, SiO and CO, resulting in depletion of the liquid phase, and, consequently, in inferior final densities and mechanical properties. Concerning the SiO2/Y2O3 additive system, the reactions seem to be completed already at temperatures below 1900 °C, turning this additive mixture unsuitable. The microstructural analysis indicated only the presence of the β-SiC phase for all samples; no phase transformation of the β-SiC into α-SiC has been observed.

Properties of SiC Ceramics Sintered via Liquid Phase Using Al2O3 + Y2O3, Al2O3 + Yb2O3 and Al2O3 + Dy2O3 as Additives: a Comparative Study

“…SiC ceramics have many applications because they allow the combination of important properties such as low density, high elastic and rupture modulus, high thermal shock resistance, and high resistance to corrosion and oxidation at high temperatures [1][2][3][4][5][6][7][8][9][10][11][12][13] . One of the properties of SiC ceramics that limits many applications is their low fracture toughness.…”

“…One of the properties of SiC ceramics that limits many applications is their low fracture toughness. Research investments have been made in the control or improvement of this property using additives in liquid phase sintering, as well as in the control of morphology and grain size during sintering and post-sintering heat treatments 9,10 . Various additives have been studied for the formation of this liquid phase in order to improve sintering and promote the formation of favorable microstructures with higher fracture toughness values than the existing ones.…”

“…Examples of well known additives are mixtures of Al 2 [2][3][4]9,10] . Among the aforementioned rare earth oxides, the one best known for production of the liquid phase during sintering is Y 2 O 3 , which appears in numerous publications [1][2][3][4][5][6][7][8][9][10][11][12][13] . Yttrium is one of the four most abundant rare earths and dysprosium and ytterbium occupy the eighth and ninth place 13,14 .…”

Fabrication of particle dispersed inert matrix fuel based on liquid phase sintered SiC

“…This problem can be solved by the use of oxide additives (e.g. Y 2 O 3 and Al 2 O 3 ) which together with SiO 2 , always present on the surface of the SiC particles, decrease the temperature of the sintering through the formation of liquid phase [5][6][7]. So-called liquid-phase sintered silicon carbide (LPS-SiC) possesses fracture toughness and strength values which are even higher then those of solid state sintered SiC [8,9].…”

Sinterização de SiC via fase líquida usando mistura de La2O3 e Al2O3 - microestrutura e propriedades mecânicas

“…Após essa preparação, a amostra é submetida a um teste de flexão, de tal modo a provocar a abertura da trinca. As equações seguintes são utilizadas para o cálculo da tenacidade à fratura (CALLISTER, 2000, SAKAI;BRADT, 1993;MEKKY;NICHOLSON, 2006;MAZZEI, 2002;STRECKER et al 1999):…”