Investigation of the chemical vicinity of crystal defects in ion-irradiated Mg and a Mg-Al-Zn alloy with coincident Doppler broadening spectroscopy

Abstract

Crystal defects in magnesium and magnesium based alloys like AZ31 are of major importance for the understanding of their macroscopic properties. We have investigated defects and their chemical surrounding in Mg and AZ31 on an atomic scale with Doppler broadening spectroscopy of the positron annihilation radiation. In these Doppler spectra the chemical information and the defect contribution have to be thoroughly separated. For this reason samples of annealed Mg were irradiated with Mg-ions in order to create exclusively defects. In addition Al-and Zn-ion irradiation on Mg-samples was performed in order to create samples with defects and impurity atoms. The ion irradiated area on the samples was investigated with laterally and depth resolved positron Doppler broadening spectroscopy (DBS) and compared with preceding SRIM-simulations of the vacancy distribution, which are in excellent agreement. The investigation of the chemical vicinity of crystal defects in AZ31 was performed with coincident Doppler broadening spectroscopy (CDBS) by comparing Mg-ion irradiated AZ31 with Mg-ion irradiated Mg. No formation of solute-vacancy complexes was found due to the ion irradiation, despite the high defect mobility.

Coincident Doppler‐broadening spectroscopy of Si, amorphous SiO2, and α‐quartz using mono‐energetic positrons

“…The CDB spectrometer at NEPOMUC, benefits from the high beam intensity that amounts to 9x10 8 moderated positrons per second [3]. This allowed, e.g., CDBS on ion irradiation induced defects in Mg-based alloys [4]. More recently, metallic layered systems based on Al and Sn were studied with the mono-energetic positron beam in order to reveal elemental information of the embedded Sn-layer in the Almatrix with unprecedented elemental selectivity [5].…”

The NEPOMUCupgradeand advanced positron beam experiments

“…The CDB spectrometer enables defect studies by conventional DBS and element-specific measurements with CDBS in the near-surface region and in the bulk of the specimen up to a positron implantation energy of 30 keV with a lateral resolution of 300 µm [37,38]. DBS can be performed in the single mode with a typical photo peak single count rate of 3-5 × 10 4 s −1 and an energy resolution of < 1.4 keV at 511 keV.…”

Doppler‐broadening (DB) measurement of ionic liquids using a monoenergetic positron beam

“…The Cu-crucible is mounted in the CDB spectrometer [3] located at the high intensity positron source NEPOMUC -NEutron induced POsitron source MUniCh [4]. The positron intensity at the sample position is 2 · 10 6 moderated positrons per second and the beam diameter is below 1 mm.…”