Defect Imaging and Detection of Precipitates Using a New Scanning Positron Microbeam

Abstract

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 $33\mu$m over a large scanning range of $19\times 19$mm${}^2$. 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 $1\times 1$mm${}^2$ ($100\times 100\mu$m${}^2$) with a resolution of $250\mu$m ($50\mu$m). We studied the defect structure in laser beam welds of the high-strength agehardened 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.

References in corpus (6)

• Positrons in Surface Physics
• Positron spectroscopy of point defects in the skyrmion-lattice compound MnSi
• Investigation of the chemical vicinity of crystal defects in ion-irradiated Mg and AZ31 with coincident Doppler broadening spectroscopy
• High-Intensity and High-Brightness Source of Moderated Positrons Using a Brilliant gamma Beam
• Detection and imaging of the oxygen deficiency in single crystalline YBa${}_{\text{2}}$Cu${}_{\text{3}}$O${}_{\text{7}-\delta }$ thin films using a positron beam
• Quality of Heusler Single Crystals Examined by Depth Dependent Positron Annihilation Techniques

Cited by in corpus (6)

• Perspective: Challenges and Transformative Opportunities in Superconductor Vortex Physics
• Impact of Oxygen Diffusion on Superconductivity in YBa${}_2$Cu${}_3$O${}_{7-\delta }$ Thin Films Studied by Positron Annihilation Spectroscopy
• Novel Data Analysis Tool for the Evaluation of Coincidence Doppler Broadening Spectra of the Positron-Electron Annihilation Line
• Breakdown of the Arrhenius Law of the Temperature Dependent Vacancy Concentration in fcc-Lanthanum
• Absolute fraction of emitted Ps determined by GEANT4 supported analysis of gamma spectra
• Total-Reflection High-Energy Positron Diffractometer at NEPOMUC -- Instrumentation, Simulation and First Measurements