IN SITU TEM OBSERVATION OF NUCLEATING AND PROPAGATING OF MICROCRACKS IN STAINLESS STEEL UNDER TENSION
不锈钢微裂纹形核扩展的TEM原位观察

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. The elastic DFZ is gradually thinned and the stress in DFZ will reach the cohesive strength resulting in nucleating of nanocracks in DFZ and blunting into voids. If continuously tensioning after crack tip emitted dislocations, and inhomogeneously thinning ahead of crack tip, then initiating and connecting of micro-voids(or micro-cracks) will be observed rather than DFZ, initiating of nanocracks and nanocracks' blunting into voids. The inversely piled-up dislocations ahead of a loaded crack tip can move towards the crack tip if unloading a little.