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Hydrogen Interaction with Vacancies in Electron Irradiated Niobium

100%

Čižek J., Procházka I., Brauer G., Anwand W., Gemma R., Nikitin E., Kirchheim R., Pundt A.

Acta Physica Polonica A

2008

vol. 113

issue 5

1293-1299

Defect studies of Nb irradiated with 10 MeV electrons were performed in the present work by means of positron annihilation spectroscopy. The lattice defects were characterized by positron lifetime spectroscopy. Moreover, defect depth profiles were studied by slow positron implantation spectroscopy. The experimental investigations were accompanied by first principles theoretical calculations of positron parameters. It was found that irradiation-induced vacancies in Nb specimens are surrounded by H, which causes a shortening of the lifetime of trapped positrons. The influence of a Pd and Cr over-layer on the H concentration in the Nb specimens was examined.

Microstructure, Thermal and Mechanical Properties of Non-Isothermally Annealed Al-Sc-Zr and Al-Mn-Sc-Zr Alloys Prepared by Powder Metallurgy

100%

Vlach M., Stulíková I., Smola B., Císařová H., Piešová J., Daniš S., Gemma R., Tanprayoon D., Neubert V.

Acta Physica Polonica A

2012

vol. 122

issue 3

439-443

This paper reports results of a study aimed at understanding the precipitation processes occurring during the annealing of two Al-Sc-Zr-based alloys with and without Mn prepared by powder metallurgy with subsequent hot extrusion at 350°C. Samples were isochronally annealed up to ≈ 570°C. Precipitation behaviour was studied by electrical resistometry and differential scanning calorimetry. Mechanical properties were monitored by microhardness HV1 measurements. Transmission electron microscopy examinations and X-ray diffraction of specimens quenched from temperatures of significant resistivity changes helped to identify the microstructural processes responsible for these changes. Fine (sub)grain structure develops and fine coherent Al_3Sc and/or Al_3(Sc,Zr) particles precipitate during extrusion in both alloys. The distinct changes in resistivity (at temperatures above ≈ 330°C) of the Al-Mn-Sc-Zr alloy are mainly caused by precipitation of Mn-containing particles. The easier diffusion of Mn atoms along the (sub)grain boundaries is responsible for the precipitation of the Al_6Mn and/or Al_6(Mn,Fe) particles at relatively lower temperatures compared to the temperature range of precipitation of these particles in the classical mould-cast Al-Mn-Sc-Zr alloys The apparent activation energy for precipitation of the Al_3Sc and Al_6Mn particles in the Al-Mn-Sc-Zr alloy was determined as (106 ± 10) kJ mol^{-1} and (152 ± 33) kJ mol^{-1}, respectively.

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2 Acta Physica Polonica A

1 2012

1 2008

2 Gemma R.

1 Anwand W.

1 Brauer G.

1 Císařová H.

1 Daniš S.

1 Kirchheim R.

1 Neubert V.

1 Nikitin E.

1 Piešová J.

1 Procházka I.

1 Pundt A.

1 Smola B.

1 Stulíková I.

1 Tanprayoon D.

1 Vlach M.

1 Čižek J.

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Hydrogen Interaction with Vacancies in Electron Irradiated Niobium

Microstructure, Thermal and Mechanical Properties of Non-Isothermally Annealed Al-Sc-Zr and Al-Mn-Sc-Zr Alloys Prepared by Powder Metallurgy