Mechanism of blister formation on tungsten surface

Mechanism of blister formation by ion beam irradiation on tungsten surface was investigated by changing the carbon concentration of 0.07–1.00%, beam fluence of 1022–1025 m−2 at beam energy and sample temperature of 1.0 keV and 653 K, respectively. When the carbon concentration was between 0.15 and 0.35%, a small number of blisters were observed in the irradiated region. When the carbon concentration was more than 0.35%, a large number of blisters with various sizes were observed all around the surface. Threshold value of beam fluence for the blister formation was around 3.0×1023 m−2 at a carbon concentration of 0.70–1.00%. Blisters with a number of about 6 mm−2 were observed at the fluence of 3.1×1023 m−2. The number of blisters was increased to 300–400 mm−2 at the fluence in the order of 1024 m−2. Larger sizes of blisters were observed with increasing of beam fluence. Atomic concentration in the irradiated region was examined by XPS. When blisters were observed, all of tungsten atoms at the depth of ∼6 nm combined with carbon atoms and formed tungsten carbide.