Joumal of the American Ceramic Sociery-Kovar et al. Vol 8I. No 4 6000 abdz 4,000 3,000 SiN, in Interphase( Fig 3. Nominal strength(o)and work-of-fracture(WOF), plotted versus the Si3N4 content in the interphase contain no Si3 NA in the interphase is probably due to manu- crack deflection is apparent between Si3N4 layers, the lengths facturing defects that were present in this billet of the delamination cracks are extremely short(<100 um) The lengths of the delamination cracks in the other materials () Crack Deflection and Delamination Cracking also are dependent on the composition of the interphase be- SEM micrographs of the side surfaces of representative tween the Siy N4 layers. For example, long delamination cracks specimens after testing are shown in Figs. 4(aH(d). Cracks are are observed between almost every SigNa layer in the materials deflected between almost every layer until the Si3N4 content in the the interphase is increased to 80 vol%, no crack deflection is observed in the specimen that contains 80 vol% SiN4 in the content in the interphase is increased to 25 and 50 vol% SigN interphase. In Fig. 5, a higher-magnification micrograph of the in the interphase. The delamination cracks in these materials side surface is shown for a specimen that contains 50 vol% are observed to kink out of the interphase after propagating Si3N4 in the interphase. This micrograph shows that, although only a short distance. Unfortunately, it is difficult to quantify 4 Fig 4. SEM micrographs of the side surface of flexural specimens containing(a)10,(b)25, (c)50, and (d)80 vol%Si, N4 in the interphase(after testing). Crack deflection is observed for specimens containing up to 50 vol% Si, N4 in the interphasecontain no Si3N4 in the interphase is probably due to manu￾facturing defects that were present in this billet. (3) Crack Deflection and Delamination Cracking SEM micrographs of the side surfaces of representative specimens after testing are shown in Figs. 4(a)–(d). Cracks are deflected between almost every layer until the Si3N4 content in the interphase is increased to 80 vol%; no crack deflection is observed in the specimen that contains 80 vol% Si3N4 in the interphase. In Fig. 5, a higher-magnification micrograph of the side surface is shown for a specimen that contains 50 vol% Si3N4 in the interphase. This micrograph shows that, although crack deflection is apparent between Si3N4 layers, the lengths of the delamination cracks are extremely short (<100 mm). The lengths of the delamination cracks in the other materials also are dependent on the composition of the interphase be￾tween the Si3N4 layers. For example, long delamination cracks are observed between almost every Si3N4 layer in the materials that contain 0 vol% and 10 vol% Si3N4 in the interphase. How￾ever, the delamination distances decrease rapidly as the Si3N4 content in the interphase is increased to 25 and 50 vol% Si3N4 in the interphase. The delamination cracks in these materials are observed to kink out of the interphase after propagating only a short distance. Unfortunately, it is difficult to quantify Fig. 3. Nominal strength (s) and work-of-fracture (WOF), plotted versus the Si3N4 content in the interphase. Fig. 4. SEM micrographs of the side surface of flexural specimens containing (a) 10, (b) 25, (c) 50, and (d) 80 vol% Si3N4 in the interphase (after testing). Crack deflection is observed for specimens containing up to 50 vol% Si3N4 in the interphase. 1006 Journal of the American Ceramic Society—Kovar et al. Vol. 81, No. 4