Crystallographic orientation dependent of blisters formation on tungsten surface exposed to helium ions

Abstract

ABSTRACT The mechanism of crystallographic orientation dependent on helium-induced blister formation in plasma-facing tungsten was studied by helium implantation, scanning electron microscopy (SEM) observation, and molecular dynamics (MD) simulation. In the present work, the electropolished high-purity tungsten was exposed to 18 keV helium ions to a fluence of 1.1 × 1018 He·cm-2at room temperature. Combined with the electron backscatter diffraction (EBSD) techniques, scanning electron microscopy observations indicate that crystallographic orientation of the underlying grain controls the behavior of blister formation. It is obvious that different grains developed different morphologies after helium implantation, and the severe blisters with larger size and higher exfoliation ratio were observed on grains oriented near <100> direction. Based on the strain–stress relation obtained from MD simulation, it was found that the blisters on grains with orientation near <100> direction grows quickly and exfoliate firstly, and the severe blistering will be achieved for grains oriented near <111> direction. It could also be foreseen that much higher fluence was expected to introduce more severe blisters on grains near <111> direction.