Compressive Creep of Hot-Pressed Si 3 N 4 Ceramics Using CRE 2 O 3 -Al 2 O 3 or CRE 2 O 3 -AlN Additive Mixtures

The creep behavior of hot-pressed Si3N4 ceramics was investigated. The proposal of this work is to investigate the use of yttrium-rare earth oxide mixture, CRE2O3, produced at FAENQUIL, as sintering additive, since the cost of production of this material is 80% inferior to Y2O3. These ceramics were obtained by uniaxial hotpressing using different additive contents and mixtures (CRE2O3-Al2O3 or CRE2O3- AlN). Compressive creep tests were carried out at 13000C and 300 MPa, in air. The Si3N4-CRE2O3-Al2O3 ceramics demonstrated that the creep resistance is inversely proportional to the additive content. Mixtures with high intergranular phase content presented low creep resistance due to high oxidation and more pronounced softening of the intergranular phase. Si3N4-CRE2O3-AlN ceramics demonstrated better creep resistance with a steady-state creep rate of 7 x 10-8 s-1. This behavior is related to the a-SiAlON content, a solid solution of Si3N4 that incorporates a great fraction of intergranular phase, decreasing the amount of intergranular phase.