On the blister formation in copper alloys due to the helium ion implantation

A new approach to the blister-formation phenomenon is discussed by means of the mathematical solution on a uniformly loaded circular plate with clamped edges (circular diaphragm). In the present investigation, it was found that blister formation depends on the mechanical properties of the alloys and 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 and blistering starts. The thickness of this thin film depends on the mechanical properties of the specific metal. Once a blister cavity is formed, the deformation of the thin film to form a blister cap depends on the buildup of pressure in the cavity contingent on the implanted dose. For the present model, it is sufficient to say that 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 buildup 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 multilayer caps, support the present model.