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|Title:||Helium-Induced Blistering and Volume Swelling in Nickel|
|Author(s):||Fenske, George Robert|
|Department / Program:||Nuclear Engineering|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||The results of an experimental investigation of helium-induced blistering are presented. The goal of the research was to examine the mechanisms involved in blistering by observing the microstructure of the implanted region using transmission electron microscopy (TEM). In particular, the volume swelling was measured as a function of the implant depth, and compared to experimental skin thicknesses in order to determine if the skin separated at the maximum volume swelling, or at the end of the swelling profile.
To accomplish this, a transverse sectioning technique was developed to prepare TEM samples. A particular advantage of this technique was that it allowed one to observe the entire distribution of cavities and dislocations, as a function of the implant depth, within one sample. Complete depth distributions of the average cavity diameter, number density, and volume swelling were obtained from nickel samples implanted with 20- and 500-keV ('4)He ions. The samples were implanted to doses ranging from 2 x 10('15) to 1 x 10('18) ions/cm('2) at room temperature, 500(DEGREES)C and 900(DEGREES)C. In addition to the TEM studies, a series of foils were examined using Rutherford backscattering and elastic recoil detection to measure the helium concentration as a function of the implant depth.
The investigation revealed several factors that are important in understanding the mechanisms involved in blister formation. First, a direct comparison of measured skin-thicknesses with the location of the maximum volume swelling demonstrated that the skin separates at the peak swelling depth, not at the end of the swelling profile. Second, an examination of the assumptions that have been commonly used to predict skin-thicknesses revealed that the differences between predicted and measured skin thicknesses at low energies can be attributed to several factors. These include: (i) failure to account for volume swelling in the skin, (ii) using a Gaussian approximation to the range profile instead of one based on higher-order moments (i.e., skewness, kurtosis, etc.) or one generated with a Monte-Carlo code, and (iii) uncertainties in the electronic stopping powers. Third, beyond a certain dose, the density of cavities in the peak-swelling region decreased with increasing dose; thus indicating that cavity coalescence does occur. Finally, a calculation of the helium concentration required to fracture the load-bearing cross section between the cavities revealed that a sufficient quantity of helium was available to generate the required gas pressures. Together, these observations indicate that models based on coalescence followed by gas-driven deformation provide an accurate description of the mechanisms involved in blistering; and that given the proper information, they can accurately predict skin thicknesses at low energies.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1980.
|Date Available in IDEALS:||2014-12-14|
This item appears in the following Collection(s)
Dissertations and Theses - Nuclear, Plasma, and Radiological Engineering
Graduate Dissertations and Theses at Illinois
Graduate Theses and Dissertations at Illinois