High temperature creep of SiC densified using a transient liquid phase

Abstract

Silicon carbide-based ceramics can be rapidly densified above approximately 1850 °C due to a transient liquid phase resulting from the reaction between alumina and aluminum oxycarbides. The resulting ceramics are fine-grained, dense, and exhibit high strength at room temperature. SiC hot pressed at 1875 °C for 10 min in Ar was subjected to creep deformation in bending at elevated temperatures between 1500 and 1650 °C in Ar. Creep was thermally activated with an activation energy of 743 kJ/mol. Creep rates at 1575 °C were between 10−9/s and 10−7/s at an applied stress between 38 and 200 MPa, respectively, resulting in a stress exponent of ≍1.7.

Effect of atmosphere and sintering time on the microstructure and mechanical properties at high temperatures of α-SiC sintered with liquid phase Y2O3–Al2O3

“…2d). Another factor contributing to the existence of porosity, can be the existence of solid state reactions between the sintering additives Al 2 O 3 and Y 2 O 3 and the SiC grains, originating volatile products as the Al 2 O, Y 2 O, SiO and CO. 9,11,12,16,17 These volatile products during sintering reduce the amount of intergranular phase present and in consequence the porosity increases. Fig.…”

“…The samples presented most creep resistance when the additive ratio was 2:3 molar and when the samples were annealed in N 2 atmosphere after sintering. Jou et al 12 studied the creep of an Ar-LPS-␣-SiC, the liquid phase being Al 2 OC (10 wt.%) and deformed at temperatures between 1550 and 1660 • C. They concluded that the deformation is controlled simultaneously by bulk diffusion processes and dislocation activity. In the same line, GallardoLópez et al 13 studied the creep behaviour of an LPS-␣-SiC with a small amount of liquid phase-less than 2 vol.% Y 2 O 3 and Al 2 O 3 -and deformed at temperatures between 1575 and 1700 • C. The deformation is due to GBS controlled simultaneously by volume diffusion of point defects and dislocation activity.…”

Heat‐Resistant Silicon Carbide with Aluminum Nitride and Erbium Oxide

“…Several strategies have been investigated to optimize hightemperature properties: (1) the formation of a transient liquid phase, which could form a crystalline phase during densification 22,23 (e.g., the simultaneous addition of Al 2 O 3 and Al 4 C 3 produces a transient liquid phase as a result of Al 2 O 3 -Al 4 O 4 C or Al 2 O 3 -Al 2 OC eutectics during sintering and forms Al 2 OC in argon or AlN in nitrogen gas); 22 (2) the crystallization of the intergranular glassy film by a postsintering heat treatment 24 ; (3) the reduction of the overall additive content by colloidal processing 25 ; and (4) the use of refractive additives, such as AlN and Y 2 O 3 . 19 One opportunity for improved high-temperature properties is the use of an additive system that can be dissolved in the SiC lattice (solid-solution formation).…”

Creep and Microstructural Evolution at High Temperature of Liquid‐Phase‐Sintered Silicon Carbide

“…7,9 One of the most widely studied additive systems is Y 2 O 3 -Al 2 O 3 , especially when these components are chosen in the ratio 3:5 to form yttrium-aluminum garnet (YAG, Y 3 Al 5 O 12 ) 10,11 : the presence of crystalline YAG has been demonstrated to improve the fracture toughness at room temperature of LPS SiC. 2 The high-temperature compressive creep of SiC has been the focus of several works before, [12][13][14][15][16][17][18][19][20][21][22][23][24] although it has yet to be systematically studied. In particular, to the best of the authors' knowledge, the correlation between creep behavior and microstructural evolution in LPS SiC containing crystalline YAG as the secondary phase has only been studied once before, showing the effect of sintering time.…”