2 mpa ______________________________________20 vol sic whisker cr 10 al sub 2 o sub 3 9 0 805 u00b1 9420 vol sic whisker linde a al sub 2 o sub 3 8 6 600 u00b1 10al sub 2 o sub 3 4 620 vol sic whisker mullite 4 6 438 u00b1 5compositemullite 2 2______________________________________ the toughness as expected was a function of the orientation of the crack plane and direction with these values in table 2 being obtained from specimens in which the crack propagation direction was normal to the hot pressing axis while the crack plane was parallel to the hot pressing axis however even when the crack propagated along the plane of the whiskers parallel to the hot pressing axis average k ic value was 5 5 mpa m 1 2 for the 20 vol sic whisker al 2 o 3 composites versus approximately 4 5 mpa m 1 2 for pure al 2 o 3 observation of fracture surfaces indicated significant whisker pull out in the two types of composites listed in table 2 it will be seen that the present invention provides for the fabrication of highly dense sic whisker ceramic composites which provide a significant increase in fracture toughness over the monolithic ceramic material it is expected that these composites will be of a significant value in the form of production components which are subjected to high temperatures and pressures also the fracture toughening process whisker pull out in the composites is activated during slow crack growth fatigue and substantially increase the resistance to slow crack growth in the composite furthermore the increased slow crack growth resistance associated with the increased fracture toughness would substantially increase the lifetime of these ceramics when they are subjected to various conditions under applied stress such.