Positron microscopy was used for studies of defects induced by ball indentation or sliding on the surface of well-annealed copper samples. A focused positron beam of 24.5-keV energy was used to scan the deformed region of the indenter impression, and measurements of the annihilation line parameter were performed. In the case of ball indentation, the measured defect distribution correlates well with the von Mises stress distribution of the Hertz contact and the von Mises yield criterion. For the wear track produced by pin on disc dry sliding, an asymmetric defect distribution near the wear track is observed. It indicates the presence of a tangential force that additionally deforms the sample.
We demonstrate the application of the new experimental technique: positron probe microanalyser for studies of the defect profiles induced by milling. Metal foils of Cu, Fe and Ti were subjected to machining in a milling machine with different cutting speed. This technique revealed well-defined profiles of defects below the machined surface which was extended up to hundreds of micrometres. The extent of the profile depended on the metal and the cutting speed. The positron probe microanalyser allowed us to trace the evolution of the profile after annealing in different temperatures. Surprisingly, the high thermal stability of a few tens of micrometres thick layer adjacent to the machined surface was detected.
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