Details

Autor(en) / Beteiligte

• Gigl, T
• Beddrich, L
• Dickmann, M
• Rienäcker, B
• Thalmayr, M
• Vohburger, S
• Hugenschmidt, C

Titel

Defect imaging and detection of precipitates using a new scanning positron microbeam

Ist Teil von

• New journal of physics, 2017-12, Vol.19 (12), p.123007

Ort / Verlag

Bristol: IOP Publishing

Erscheinungsjahr

2017

Quelle

EZB Electronic Journals Library

Beschreibungen/Notizen

• We report on a newly developed scanning positron microbeam based on threefold moderation of positrons provided by the high intensity positron source NEPOMUC. For brightness enhancement a remoderation unit with a 100 nm thin Ni(100) foil and 9.6% efficiency is applied to reduce the area of the beam spot by a factor of 60. In this way, defect spectroscopy is enabled with a lateral resolution of 33 m over a large scanning range of 19 × 19 mm2. Moreover, 2D defect imaging using Doppler broadening spectroscopy (DBS) is demonstrated to be performed within exceptional short measurement times of less than two minutes for an area of 1 × 1 mm2 (100 × 100 m2) with a resolution of 250 m (50 m). We studied the defect structure in laser beam welds of the high-strength age-hardened Al alloy (AlCu6Mn, EN AW-2219 T87) by applying (coincident) DBS with unprecedented spatial resolution. The visualization of the defect distribution revealed a sharp transition between the raw material and the welded zone as well as a very small heat affected zone. Vacancy-like defects and Cu rich precipitates are detected in the as-received material and, to a lesser extent, in the transition zone of the weld. Most notably, in the center of the weld vacancies without forming Cu-vacancy complexes, and the dissolution of the Cu atoms in the crystal lattice, i.e. formation of a supersaturated solution, could be clearly identified.