纯Ni中氢致开裂的透射电镜原位观察

IN SITU TEM STUDY ON HYDROGEN-INDUCED CRACKING OF NICKEL

纯 Ｎｉ在透射电镜（ＴＥＭ）中原位拉伸时，裂纹尖端首先发射大量位错，平衡时形成无位错区，微裂纹在裂纹顶端连续形核或在无位错区中不连续形核，并且形核后将钝化成孔洞或缺口．利用特殊的恒位移加载台，可在ＴＥＭ中原位研究充氢前后恒位移试样裂尖位错组态的变化．结果表明，氢能促进位错的发射、增殖和运动 和未充氢纯Ｎｉ相比，充氢试样在更低的外应力下位错就会发射和运动，当氢促进的位错发射和运动到临界条件时就会使氢致裂纹形核、扩展，导致低应力脆断．

In situ tensile test in TEM showed that a dislocation-free zone (DFZ) formed ahead of a loaded crack tip when dislocation emission and motion reached equilibrium under keeping constant displacement, and a microcrack initiated after the dislocation emission and motion developed to a certain condition through increasing load. A constant deflection device designed for use within TEM was used to investigate the change in dislocation configuration ahead of a loaded crack tip before and after hydrogen-charging and crack initiation during charging under constant displacement. The results showed that hydrogen could enhance dislocation emission, multiplication and motion. A hydrogen-induced crack would initiate during charging under constant displacement when the hydrogen-enhanced dislocation emission and motion developed to a critical condition.