In-situ study of deformation and fracture dynamics of functional ceramics

了解材料断裂的成因是防止其破坏的关键，也是材料科学的重要课题。通过原位纳米压痕和先进显微镜相结合的研究，研究了陶瓷在纳米形变过程中的微观结构演变，并对材料断裂机理进行了探讨。也看不到位错的发射。在(0001)晶面上形成微裂纹并沿晶面扩展。卸载后，在裂纹尖端观察到位错。这表明裂纹表面发生了悬挂键的回弹和愈合。研究了晶界对立方氮化硼力学性能的影响。结果表明，立方BN中的Sigma9和Sigma3GBs倾向于捕获氧，从而显著降低了Gb的结合能，大大降低了立方BN的硬度。

Understanding of origin of materials fracture is the key point to prevent their damages, and also is an important subject of materials science. Through a combined study of in-situ TEM nanoindentation and advanced microscopy, we investigate the microstructure evolution of ceramics during nano-deformation, and study the mechanism of materials fracture.There is no obvious plastic deformation during the nanoindentation of 4H-SiC. The emission of dislocation also cannot be seen. A micro-crack is formed and propagates along on the (0001) crystal plane. After unloading, dislocations are observed at the tip of the crack. It suggests that the dangling bonds on the surfaces of crack rebound and the healing of crack take place. Effects of grain boundaries on the mechanical properties of cubic BN have been studied. It is found that Sigma9 and sigma3 GBs of cubic BN are inclined to trap oxygen, which lowers the GB adhesion energies significantly, and greatly reduces the hardness of cubic BN.