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The temperature driven segregation of Cr to the surface of the tungsten-basedWCrY alloy is analysed with low energy ion scattering of He+ ions with anenergy of 1 keV in the temperature range from room temperature to 1000 K. Dueto the high surface sensitivity, these measurements probe only the compositionof the outermost monolayer. The surface concentration of Cr increases slightlywhen the temperature of the sample is increased up to 700 K and exhibits a muchstronger increase when the sample temperature is further raised. Thesegregation enthalpy for Cr is obtained from the Langmuir-McLean relation andamounts to 0.7 eV. The surface concentration of Y shows a similar behaviour tothe Cr concentration. The temperature thresholds between slow and acceleratedsurface density increases for Cr and Y are nearly the same. At a temperature of1000 K the low energy ion scattering detects almost no W on the surface. Themodified surface composition due to the segregated species, i.e. the mixed Cr/Ylayer, stays stable during cool-down of the sample. Preferential sputtering isinvestigated using ion bombardment of 250 eV D atoms, resulting in an increaseof the W surface density at room temperature. This effect is counteracted atelevated temperatures where segregation replenishes the lighter elements on thesurface and prevents the formation of an all-W surface layer. The flux ofsegregating Cr atoms towards the surface is evaluated from the equilibriumbetween sputter erosion and segregation.

Segregation and Preferential Sputtering of Cr in WCrY Smart Alloy