摘要：The poor grain boundary strength induces low toughness failures when the principal stress acts through the thickness. On the other hand, a delamination toughening mechanism occurs when the stress is applied in longitudinal and transverse directions. During fatigue crack growth at low R load ratios a strong closure effect occurs. AES analyses on freshly broken surfaces reveal that intergranular fracture occurs also with absence from the grain boundaries not only of Li, but also of K or Na impurities.
