High temperature fracture characteristics of a nanostructured ferritic alloy (NFA)

The nanostructured ferritic alloys (NFAs) have been developed to improve high temperature strength and radiation resistance by refining grains and including nanoclusters. Among the key properties of NFAs needed to be assessed for advanced reactor applications the cracking resistance at high temperatures has not been well known. In this work, therefore, the high temperature fracture behavior has been investigated for the latest nanostructured ferritic alloy 14YWT (SM10). The fracture toughness of the alloy was above 140 MPa √m at low temperatures, room temperature (RT) and 200 °C, but decreased to a low fracture toughness range of 52–82 MPa √m at higher temperatures up to 700 °C. This behavior was explained by the fractography results indicating that the unique nanostructure of 14YWT alloy produced shallow plasticity layers at high temperatures and a low-ductility grain boundary debonding occurred at 700 °C. The discussion also proposes methods to improve resistance to cracking.