NUCLEATING, BLUNTING OR PROPAGATING OF A NANOCRACK IN DISLOCATION-FREE ZONES OF THIN-CRYSTALS

Nucleating, blunting or propagating of nanocracks in dislocation free zones (DFZs) of ductile and brittle metals have been studied through i n situ tensile tests in TEM and analyzed using micro-fracture mechanic s. The results show that in either ductile or brittle metals, many dis locations could be emitted from a loaded crack tip and a dislocation f ree zone formed after equilibrium. The stress in the DFZ might be up t o the cohesive strength and then a nanocrack initiated in the DFZ or s ometimes at the blunt crack tip. In ductile metals, a nanocrack would quickly blunt into a void or a notch during constant displacement. In brittle metals, a nanocrack would propagate into a cleavage crack rath er than blunt.