Mode Ⅰ crack tip plastic zone,dislocation-free zone and their effects on crack propagation;
Ⅰ型裂纹尖端塑性区和无位错区及其对裂纹扩展的影响
Dislocation emission from the crack tip,formation of dislocation-free zones,nucleation of nano-cracks and dislocation pile-ups were all observed.
进行了1Cr18Ni9Ti(奥氏体321型不锈钢)的TEM原位拉伸实验,观察到了位错从裂纹尖端的发射、无位错区形成、纳米裂纹形核及位错塞积等物理现象。
A dislocation free zone(DFZ) is formed between crack tip and the inversely pileup dislocations when the dislocation emission and motion reach equilibrium.
结果发现:黄铜薄膜试样拉伸时,裂尖首先发射位错,平衡时形成无位错区和反塞积位错群;裂尖前方较厚区域可以发生孪生变形,形成形变孪晶,微裂纹在孪晶中形核、扩展,导致裂纹呈Z字形扩展;裂尖无位错区也可能形成微孪晶,微裂纹在微孪晶中形核,使裂纹呈不连续扩展;微裂纹也可以从主裂纹顶端连续形核、扩展。
TEM in situ tensile tests of 310 stainless steel show that a dislocation free zone (DFZ) forms after equilibrium if the displacement keeps constant after many dislocations are emitted from a crack tip.
３１０奥氏体不锈钢在透射电镜中的原位拉伸观察表明，如在裂尖发射位错后保持恒位移，则在裂尖能形成无位错区（ＤＦＺ）。
The results show that 1)in precharged specimens,many dislocations can emit from a crack tip followed by forming a dislocation free zone(DFZ) after equilibrium:2)nanocracks nucleate preferable in DFZs;3)microcracks connect with each other,resulting in the brittle cracks,instead of blunting into voids.
结果表明，预充氢的３１０不锈钢试样在拉伸过程中从裂尖发射大量位错，平衡后形成无位错区（ＤＦＺ）；纳米级微裂纹择优在ＤＦＺ中形核；微裂纹不钝化为空洞，而是通过多个微裂纹的形核及相互连接导致裂纹的脆性扩展。