Ductile fracture mechanism in fine-grained magnesium alloys with dispersion of fine particles

三点弯曲韧性试验开始时的变形组织观察表明，裂纹尖端尖端由高角度晶界组成的组织转变为亚晶界组织，没有变形孪晶。防止孪晶的形成导致镁及其合金断裂韧性的提高，因为变形孪晶通常成为裂纹扩展的部位。另一方面，韧窝形成区不仅是亚晶界的形成，而且是纳米有序孪晶的形成。导致纳米有序孪晶形成的原因是导致颗粒开裂和/或界面断裂的应力远大于孪晶形成的应力。

The deformed microstructural observations at the beginning of the three-point bending toughness test showed that the microstructure at the head of the crack-tip composed of high-angle grain boundaries changed to that of sub-grain boundaries without any deformation twins. The prevention of twin formation led to an improvement of fracture toughness in magnesium and its alloys, since the deformation twins generally become the crack-propagation site. On the other hand, the dimple formed region showed the formation of not only sub-grain boundaries but also nano-ordered twins. The reason for the nano-ordered twin formation is that the stress to cause the particle cracking and/or interface fracture is much higher than that to form the twins.