Multi layer blister formation in structural alloys due to hydrogen and helium implantation

Blister formation phenomenon is discussed by means of the mathematical solution on a uniformly loaded circular plate with clamped edges. The investigation found that blister formation depends on the mechanical properties of the alloys and on the near-surface concentration of the implanted gas, which itself is contingent on the crystallographic orientation by means of the stopping power of the implanted atoms. The reported model is based on the fact that, at certain depths from the surface, the pressure in the cavities approaches the yield stress of the metal. The thickness of this thin cap of the metal, depends on the mechanical properties of the specific metal. Once a blister cavity is formed, the deformation of the surface to form a blister cap depends on the build-up of pressure in the cavity contingent due to the implanted dose. For the present model, the thickness of the blister's cap cannot be correlated with the projected range of the implantation, as assumed by other authors. The implanted helium concentration needed to build up enough gas pressure to create a blister at a depth which is close to the projected range is higher by 50 times than the gas helium concentration in the cavity. Experimental results, such as the fact that the blisters have burst at the edge of the circular skin, where the maximum stresses are developed, and the fact that, at high implantation energy (large projected range), the bursting of the blisters occurs by multi layer caps, support the present model.