Hannover 2020 – scientific programme
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P: Fachverband Plasmaphysik
P 5: Poster Session 1
P 5.25: Poster
Monday, March 9, 2020, 16:30–18:30, Empore Lichthof
LEIS Investigation of Cr Segregation in WCrY — •Hans Rudolf Koslowski1, Janina Schmitz1,2, and Christian Linsmeier1 — 1Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung – Plasmaphysik, 52428 Jülich, Germany — 2Department of Applied Physics, Ghent University, 9000 Ghent, Belgium
The temperature driven segregation of Cr to the surface of the tungsten-based W-11.4Cr-0.6Y (wt%) alloy is analysed with low energy ion scattering (LEIS) which probes only the composition of the outermost monolayer due to its high surface sensitvity.
The surface concentration of Cr increases slightly when the temperature of the sample is increased up to 700 K and exhibits a much stronger increase when the sample temperature is further raised. At a temperature of 1000 K LEIS detects almost no W atoms on the surface. A segregation enthalpy of 0.7 eV for Cr is obtained from the Langmuir-McLean relation. The modified surface composition due to the segregated Cr stays stable during cool-down of the sample.
Preferential sputtering is investigated using ion bombardment of 250 eV D atoms, resulting in an increase of the W surface density at room temperature. This effect is counteracted at elevated temperatures where segregation replenishes the Cr on the surface and prevents the formation of an all-W surface layer. The flux of segregating Cr atoms towards the surface is evaluated from the equilibrium between sputter erosion and segregation.