Segregation and preferential sputtering of Cr in WCrY smart alloy. (January 2020)

• Record Type: Journal Article
• Authors: Koslowski, Hans Rudolf; Schmitz, Janina; Linsmeier, Christian
• Is Part Of: Nuclear materials and energy. Volume 22(2020)
• Publication Date: 2020-01
• Subjects: Low energy ion scattering (LEIS) -- Plasma-surface interaction -- Segregation -- Preferential sputtering -- WCrY; Nuclear energy -- Periodicals; Nuclear fuels -- Periodicals; Nuclear reactors -- Materials -- Periodicals; Radioactive substances -- Periodicals; 621.4833
• DOI: 10.1016/j.nme.2020.100736
• Languages: English
• ISSNs: 2352-1791

Abstract

Highlights: Temperature driven Cr segregation to the surface of W-11.4Cr-0.6Y alloy is investigated with low energy ion scattering. Almost no W is detectable in the topmost surface layer at a temperature of 1000 K. The segregated Cr stays on the surface when the sample cools down. D bombardment with 250 eV at room temperature induces preferential sputtering of the lighter alloy components and W enrichment on the surface. D sputtering at elevated temperature results in less W surface enrichment due to the continuous flux of segregating Cr atoms. Abstract: The temperature driven segregation of Cr to the surface of the tungsten-based WCrY alloy is analysed with low energy ion scattering of He + ions with an energy of 1 keV in the temperature range from room temperature to 1000 K. Due to the high surface sensitivity, these measurements probe only the composition of the outermost monolayer. 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. The segregation enthalpy for Cr is obtained from the Langmuir-McLean relation and amounts to 0.7 eV. The surface concentration of Y shows a similar behaviour to the Cr concentration. The temperature thresholds between slow and accelerated surface density increases for Cr and Y are nearly the same. At a temperature of 1000 K the low energy ion scattering detects almost no W on the surface. The modified surface composition due to the segregated species, i.e. the mixed Cr/Y layer, 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 lighter elements 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.