Fatigue-Induced Nanoscale Patterns and Microstructures

摘要: Dislocation patterns as produced by monotonic loading of polycrystalline aluminum or fatigue a low-alloy ferrltic steel have been evaluated. A proposed theoretical model Involves an accounting procedure based upon dislocations emanated at grain boundary sources being stored in dislocation series subcells. Near equilibrium, the scale parameters are roughly 100 µm grains divided into 1µ subcells which contain spaced about 10 nm Intervals within cell walls. Pattern generation and spacings dictated quasi-static state equilibrium during workhardening phase loading. Experimental nanometer-scale probes, used study, consisted three forms electron microscopy. The first involved direct imaging intersecting slip free surface electropolished samples, using channeling contrast from back-scattered electrons (BSE). second use selected-area (SACP’s) to evaluate crystallography defect densities, while third directly evaluated sizes with transmission microscopy thin films (TEM). BSE, SACP TEM probes determined be packed walls wave length 0.78 interwall spacing 33nm, consistent model. BSE revealed elliptical develop single SACP’s verified that these were sharp valleys crystallographic misorientation 17 degrees across valley. One those was shown lead crack nucleation transgranular mode.