CORRELATION BETWEEN IRRADIATION DAMAGE AND MICRO-MAGNETIC PROPERTIES FOR REACTOR STEELS
Magnetic domain structures are strongly influenced by material microstructures including crystal structures and defects. Correlations via microstructure between mechanical properties of steels and their magnetic properties invites the use of magnetic techniques to assess their microstructure. The vision of this work is to correlate magnetic characterizations and computational modeling to simulate progression of microstructural changes and predict resulting magnetic signatures in nuclear reactor structural steels using magnetic non-destructive evaluation (NDE) measurements. In this work, we used focused ion beam milling to create different shapes in various crystallographic orientation in single crystal, polycrystalline, and irradiated single crystal iron thin films. Magnetic force microscopy images and simulations assess the behavior of domain walls as they propagate in the presence of an applied magnetic field. The single crystal Fe film is the first step to develop and validate initial models. Various domain structures can be observed in experimental measurements is mainly due to the sophisticated energy competition in the sample that resulted in diverse metastable phase at remanence state. Different boundary conditions, geometries as well as experimental manipulation are the additional factors that may alter the demagnetization energy and anisotropy energy inside of the system. Further studies in irradiated single crystal iron thin film samples proved that irradiation-induced defects in structural alloys will cause microstructural changes that alter the magnetic domain wall behavior under external applied magnetic field. High dose irradiation induced the creation of more defects and dislocations, which are pinning sites that provided more resistance to domain wall movement. In polycrystalline iron thin films, the misorientations of the grains generate local magnetic free poles along grain boundaries so there will be local internal stresses which increase the total magnetostatic energy and magnetoelastic energy. Various domain structures are formed to reduce the energy of the system and the magnetic free pole density can be used to determine the types of domain structure. Future studies will assess more complicated and representative multiphase alloys. The ultimate goal is to leverage materials sciences, computational methods, and physical property imaging to monitor materials behavior in nuclear power reactors, and provide predictive models for degradation and remaining life of components.