| Abstract: |
The Positron Annihilation Spectroscopy (PAS) is nowadays a well established and versatile probe method for non-destructive testing of lattice defects produced by plastic deformation. Defect concentrations in metals of 10-6 per Atom can be detected in the annihilation signal. The Bonn Positron Microprobe (BPM), developed at the Helmholtz Institute for Beam and Nuclear Physics, provides a fine focus positron beam for the spatially resolved detection of lattice defects in the micron range. The aim of the project was an imaging of the defect distribution in the shear zones and the forward deformation zone as well as the analysis of the influence of the cutting parameters on the damaging depth in the surface near layer. An empiric dependency between the S-Parameter and the hardening could be determined by analysing tensile tests. A distinct correlation between the S-Parameter and the Vickers-Hardness could also be found. A special sample geometry, which was developed in cooperation with the Institut für Fertigungstechnik und Werkzeugmaschinen (IFW) in Hannover, affords a 2-dimensional scanning of the defect density inside a chip root. This showed a direct influence of the depth of cut on the damage depth in the surface near layer, while no influence of the cutting speed at constant depth of cut was observed. One sample showed a softening in the scanning positron image, that was ascribed to temperature set free during cutting. |
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