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

Abstract

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.

The Influence of Crystal Orientation and Thermal State of a Pure Cu on the Formation of Helium Blisters

“…After 20 min of heat treatment, the mean blister area and the blister number density of the (111) plane reached a plateau, which was probably due to the equality of both the nucleation and growth rates. The blisters on the (100) planes showed a slightly different tendency after 20 min of heat treatment; the mean blister area reached a steady state, and the blister number density continued to As illustrated in Figure 11a, larger blisters were created on (100) surfaces compared with (111)-oriented grains at all heat treatment time intervals, which agrees with the results of Moreno et al [23] for a copper single crystal. The (100) orientation also exhibited a higher blister number density compared with the (111) orientation (Figure 11b), indicating that (100) surfaces are more susceptible to blistering.…”

“…Each experimental point is based on blister in the total grain area varying between 109,000 and 567,000 µm 2 (hundreds of grains). As illustrated in Figure 11a, larger blisters were created on (100) surfaces compared with (111)-oriented grains at all heat treatment time intervals, which agrees with the results of Moreno et al [23] for a copper single crystal. The (100) orientation also exhibited a higher blister number density compared with the (111) orientation (Figure 11b), indicating that (100) surfaces are more susceptible to blistering.…”

“…Our results show that some orientations are more sensitive to blister formation. Previous research has shown the preference of certain surfaces in polycrystalline tungsten [36] and in Cu single crystals [23]. A comprehensive explanation of all the phenomena observed in this work appears to be challenging, and more work needs to be conducted.…”

“…Both models assume that the driving force for helium blister formation is the internal liberation of helium and its accumulation in the near-surface region [18]. Blister formation depends on the composition of the implanted material and its crystallographic orientation, thermo-mechanical history, and the experimental temperature [19][20][21][22][23]. Studies on different metals have been performed to understand the dependence of blister formation on the crystallographic orientation.…”

“…While no blisters were found on the (110) free surface, the largest blisters were formed on (100) faces. This phenomenon is explained by the depth reached by helium ions below the surface, which is influenced by the stopping power of each grain orientation [23]. Microstructural defects, such as dislocations, vacancies, and grain boundaries, can significantly affect the behavior of helium in a material [24,25], particularly in terms of its ability to form bubbles and blisters, as detailed in the discussion.…”