Figure 4. SEM of whisker pullout on fracture surfaces of Si3N4 composite: (A) 1 day, (B) 400 days, and (C) 730 days of water-aging, with shorter whisker pullout at 400 and 730 days. Polymer remnants were observed on the pulled-out whiskers (arrows), indicating good whisker-polymer matrix bonding even after 730 days of water-aging.