Mullite composites fracture toughness

In this study the effect of texture on fracture toughness was studied by varying the template s aspect ratio. SEM analyses were done for microstmeture characterization. Rocking curve was done to quantify the orientation distribution of mullite grains in the mullite/zirconia composite. Elastic modulus, strength, hardness and toughness of the composites were measured and correlated to the textured microstructure. 

The fracture toughness values of mullite and various composites was determined using an indentation-fracture technique. Vickers diamond-pyramid measurements were made on polished specimens perpendicular to the hot-pressing direction using a 3 kg indentation load. This load produced cracks and hardness impressions of reasonable dimensions. 

FIGURE 13. Fracture toughness versus SiC whisker content in mullite-SiC whiskerand nmllite-Zr02-SiC whisker composites. Published with permission ofthe J. Am. Ceram. Soc. (15)... 

Magnesium aluminosilicate glass composites with 3-D mullite whisker reinforcement Fracture strength 330 MPa. Fracture toughness 3.3 MPam Structural applications requiring isotropic mechanical properties [30]... 

P-SiC whiskers have been added to a wide variety of ceramics (AI2O3, Si3N4, AlN, MoSi2, mullite, cordierite, and glass ceramics) in an effort to achieve increased toughness. A real success story in the advanced ceramic market was the introduction of hot-pressed alumina reinforced with 25-30 wt% SiC whisker, such that a composite with increased strength (by over 50%), fracture toughness (by 100%),... 

Claussen and Jahn ° were the Erst researchers to show that the mechanical properties of mullite could be improved by the dispersion of zirconia particles. Fracture toughness improved from 2.0 to 4.5 MPa-ml4 and the strength doubled to 400 MPa. They were able to fabricate the dense (>98% theoretical density (T.D.)) mullite-zirconia composite at relatively low sintering temperatures of 1575-1600 °C by the in-silu reaction of alumina and zircon to form mullite with approximately 25 vol% zirconia ... 

---