Abstract
The stress rupture properties of high nickel austenitic alloys and austenitic stainless steels used in the nuclear industry are strongly affected under irradiation by the formation of helium from boron by means of an n-α reaction. As the congregation and growth of helium bubbles (typically 20-50nm diameter) at grain boundaries can cause embrittlement in stressed steels, it is important to gain an understanding of embrittlement mechanisms in the material. Consequently, an accurate measurement of quantities such as bubble pressure and metal surface energy is highly desirable. However, this can only be achieved if the number of helium atoms per unit volume is known. In this work, we report on the use of parallel-detection electron energy loss spectroscopy (PEELS) on a VG HB501 scanning transmission electron microscope (STEM) as a powerful technique for characterising helium bubbles in irradiated steels. In addition, we suggest a simple analytical process that could be used to quantify the amount of helium present in each bubble.
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