2011 Volume 97 Issue 5 Pages 266-272
We have developed positron probe microanalyzer (PPMA) for obtaining two-dimensional map of open-volume type defects. The primary positron beam with 4 mm diameter was guided in a static magnetic field, followed by focusing to the Ni(100) foil with 150 nm thick for the brightness enhancement. The remoderated positron beam re-emitted from the Ni foil was accelerated and focused to the specimen by the magnetic objective lens. The focused beam diameter was estimated to be 14.5 μm. PPMA has been applied to investigate the defect behavior in a plastic deformation for polycrystalline high-purity Fe and Fe–0.5mass%Cu alloy samples, and Doppler broadening of the positron annihilation line has been used to map the defect distribution. The results showed that the defects were heterogeneously introduced by deformation and the concentration of the defects was high in a necking region. This can be attributed to the inhomogeneous deformation in the polycrystalline sample. A formation of vacancy clusters in the vicinity of the fractured point is suggested by a large change in Doppler broadening of the positron annihilation line. It has been, further, proven that Cu precipitation in Fe–0.5Cu alloys by annealing is enhanced by the defects induced by a plastic deformation.
