Understanding degradation of nuclear steels using micro-mechanical methods

Nuclear grade steels are widely used across the nuclear industry in a wide range of structural applications. Typically in these environments they are exposed for long time periods (upto 80 years in future civil reactors) to high temperatures and radiation damage. This can result in degradation of mechanical properties through formation of new precipitates and phases which are not seen at shorter time periods at lower temperatures or without radiation damage. Simulation of this is difficult and so called thermal aging treatments are used to accelerate the formation of phases. Whilst much is understood about the chemical and microstructural changes how this effects the mechanical properties is less well understood. This project will develop in-situ high temperature micro-mechanical methods to study the degredation induced in these samples and compare it to conventional macroscopic data, produced by industrial collaborators.

The proposed project involves the application of a range of micromechanical techniques to specific nuclear steels; the mechanical properties of most interest are yield strength, work hardening behaviour, hardness and fracture toughness.  A range of materials of key interest will be studied in the datum condition and after irradiated by ion implantation or test reactor exposure as appropriate. Testing will be carried out from room temperature to reactor specific temperatures in vac (likely 350oC). Thermal ageing post exposure will be explored for selected samples. For the samples which show the most change or interesting results additional in-situ tests will be performed in the SEM, using a newly purchased Pico Indenter. This will allow direct observation and local strain measurements to be by developing robust methods for performing DIC on these tests.

Typical specimen length scales are sub-micron to tens of microns and test geometries include tensile tests, compression and micro-bending. This small scale offers radically reduced difficulty and costs associated with testing irradiated materials. The small size of the tests, however, creates a size effect in the results that must be understood in detail to maximise the usefulness of the micromechanical testing results. These methods are widely used in other projects involving industrial collaborators studying both fundamentals of deformation as well as in service materials failures in a range of materials including titanium alloys, nickel super alloys and ceramic composites. This project is expected to have additional industrial funding confirmed in January 2019.

The description above outlines a possible new research project being offered to prospective new postgraduate students.

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