This direction addresses property degradation of nuclear power plant and aero-engine components in long-term service, and studies microstructural evolution and failure modes under thermal ageing, irradiation, hydrogen and corrosion, acting separately or together.

For cast duplex stainless steel, spinodal decomposition and G-phase precipitation in ferrite during long-term ageing at 400 C are followed, and their relation to the loss of impact toughness and to brittle fracture is measured, providing criteria for thermal ageing assessment of primary coolant piping. For welded joints, microstructure and residual stress are compared among weld metal, heat-affected zone and base metal in dissimilar-metal safe-end joints, and property changes are tracked after long-term service. For zirconium alloys, hydride location, orientation and stress-induced reorientation are studied, together with the manifestation of hydrogen-induced damage under tension and fatigue. For irradiation damage, ion irradiation is used to simulate neutron irradiation, and the evolution of dislocation loops, dislocation cells and solute segregation in austenitic stainless steels and iron-based alloys is observed, with an explicit statement of the limits that apply when extrapolating ion irradiation results to in-reactor conditions.

All four parts share one logic: service conditions as input, microstructural parameters as intermediate variables, macroscopic mechanical properties and failure modes as output, in a form that supports comparison across datasets.