Investigation of production parameters in fracture behavior of hot-pressed Al2O3-SiC/graphite fibrous monolithic ceramics: Fibers orientation and cell boundary fraction

Fibrous monoliths (FMs) exhibit graceful failure in flexure and have higher toughness values. In this research, a mixture of Al2O3 and SiC as the core and graphite as the shell material of fibers were produced by extrusion-molding technique and after aligning along intended directions (0 degrees, 90 degrees, and 0 degrees/90 degrees) were sintered using the hot-pressing method at the temperature of 1500 degrees C under pressure of 35 MPa for 1 hour. The significance of fibers orientation angle and the cell to cell boundary volume ratio in defining the fracture behavior of the FMs was detected. Because of the extensive crack interactions with graphite cell boundary such as crack deflection and delamination, with increasing cell boundary content from 25 to 30 vol%, the fracture toughness was enhanced. The highest flexural strength (184.8 +/- 0.61 MPa) obtained from samples with 0 degrees fibers orientation compared to 0 degrees/90 degrees. Since in the transverse plies (layers with 90 degrees aligning), the properties of matrix phase are dominant, hence the strength in specimens with 0 degrees/90 degrees fibers orientation decreased considerably due to weak graphite matrix phase. In addition, the fracture toughness value increased up to 8.35 +/- 0.74 MPa center dot m(1/2) for the unidirectional architecture of (0 degrees) in comparison with cross-ply (0 degrees/90 degrees) architecture.