By SEM it has been found that, with the increase of aging time, the fracture model changes from predominantly transgranular at underaged condition to intergranular at overaged condition.

• 扫描电镜观察发现：随时 效的进行，断裂模式从欠时效状态下以穿晶断裂为主向过时效状态下 以沿晶断裂为主变化。