in psz the tetragonal to monoclinic crystallographic martensitic transformation occurs preferentially in the stress field at crack tips and not in the bulk of the material the volume change associated with the transformation lowers crack tip stresses thus increasing the fracture toughness of the composite material the high temperature effects would occur due to a dispersion strengthening effect on dislocation motion at elevated temperatures in a similar fashion to the high temperature strengthening effects which have been observed for sic whisker and sic particle reinforcements of mosi 2 the improvement in properties of a mosi 2 matrix by adding fsz to it is not due to transformation toughening but is probably crack deflection toughening zirconia is very stable and its low thermal conductivity makes it desirable as a structural insulator monolithic zirconia materials while possessing high fracture toughness at low temperatures due to a transformation toughening effect lose their toughened characteristics as the temperature is increased because the martensitic transformation responsible for the toughening reduces in extent with increasing temperature typically all transformation toughening is lost at temperatures above approximately 900 u00b0 c however mosi 2 begins to exhibit plastic deformation above 900 u00b0 1000 u00b0 c thus the presence of mosi 2 particles in zirconia matrices could lead to significant improvements in the elevated temperature mechanical properties of these matrices such as fracture toughness strength and crack growth behavior above 1000 u00b0 c mosi 2 particles act as ductile metal particles in restraining the initiation and propagation of brittle cracks in the zirconia matrix by means of plastic deformation energy absorption mosi 2 toughening effects increase with increasing.