Irradiation-induced microstructure and microchemistry effects on mechanical properties in ferritic-martensitic alloys

Abstract

Ferritic-martensitic alloys have emerged as candidates for structural and cladding applications in advanced reactors but are known to experience irradiation-induced changes to their microstructures (including solute clustering), leading to changes in their mechanical properties. Irradiation of three commercial alloys (HT9, HCM12A, and T91) with Fe2+ ions to 3 dpa is found to result in varying degrees of hardening of the materials, consistent with prior TEM- and APT-based microstructure observations. As irradiation dose is increased to 100 dpa, partial softening is observed in both HCM12A and T91. Matrix solute concentrations are observed to decline at higher dose and are likely contributing to the softening, with evidence of segregation of solutes to more stable sinks at higher dose. Analysis methods combining the dispersed barrier hardening and solid solution strengthening effects are successful at correlating microstructures to mechanical properties using a combined effective diameter approach to represent complex Cu-rich nanoclusters with Si-Mn-Ni-rich appendages.