Direct Studies of Fracture Mechanisms in Metals at Highest Magnification

摘要

Techniques for in-situ straining to fracture were developed for use in high voltage and conventional transmission electron microscopes in order to record the dynamical features preceding crack initiation and subsequent crack propagation in ductile metals. Eight pure metals and alloys have been investigated. It was discovered that dislocation cell walls are the primary sites for microcrack initiation, even in alloys which contain soft second phase particles. Ligament fracture was found to occur by shear which, in low stacking fault metals, was by translation and twinning. The presence of micro-voids and cell wall remnants affected the zig-zag geometry of the crack flank. For macroscopic rupture and for cup-and-cone fracture, the final separation took place by rupture processes in the microstructural regime. (Author)