Dislocation-defect interactions in nuclear reactor pressure-vessel steels investigated by means of internal friction

A study of pressure-vessel steel embrittlement mechanisms by means of temperature-dependent and amplitude-dependent internal friction has been carded out within the framework of commercial surveillance of nuclear reactor components. An inverted torsion pendulum operating at approximately 1 Hz has been employed to study a wide variety of pressure-vessel steels and an IAEA reference material in various conditions. This contribution will discuss the results for the JRQ reference material only and serve as a basis on which to interpret the data from real pressure-vessel steels. The temperature-dependent experiments evidence a reduction in the dislocation mobility as a result of neutron irradiation and prove that the technique is sensitive to thermal ageing involving changes in the dislocation mobility and type of dislocation-defect interaction. Amplitude-dependent internal friction provides a means to determine the yield strength of the material. The importance of the influence of dislocation dragging on the yield stress is highlighted.