Effect of severe plastic deformation on surface modification of tungsten exposed to low energy helium ion irradiation

The orientation dependence of the surface morphology for polycrystalline W after the He plasma exposure (similar to 50 eV) at similar to 823 K was systematically investigated. Five different types of undulating morphologies were formed and the edge direction of the undulations was parallel to the < 100 > orientation. The relationship among crystal orientation, undulating height and undulating interval was established and the interval coefficient was introduced. The interval and the interval coefficient gradually increase until the tilting angle increases to 36 degrees. After severe plastic deformation (SPD), the undulating height increased from 5.7 nm for the as-received W to 11.9 nm for the SPDed W and the surface roughness of the SPDed grains increased significantly. Reducing the grains with the {100} plane and inhibiting the formation of unstable nanostructures are helpful to slow down the volume loss of W and improve its irradiation resistance.