Cluster dynamics modeling of Mn-Ni-Si precipitates in ferritic-martensitic steel under irradiation

TL;DR

This paper develops a cluster dynamics model incorporating dislocation effects to predict Mn-Ni-Si precipitate evolution in ferritic-martensitic steel under irradiation, validated by proton irradiation data.

Contribution

It introduces an advanced cluster dynamics model that includes dislocation effects and radiation-induced segregation to better predict precipitate behavior under irradiation.

Findings

MNSPs are primarily irradiation-induced in T91 steel.

Heterogeneous nucleation on dislocations is essential for precipitate formation.

Radiation-induced segregation at dislocations influences precipitate evolution.

Abstract

Mn-Ni-Si precipitates (MNSPs) are known to be responsible for irradiation-induced hardening and embrittlement in structural alloys used in nuclear reactors. Studies have shown that precipitation of the MNSPs in 9-Cr ferritic-martensitic (F-M) alloys, such as T91, is strongly associated with heterogeneous nucleation on dislocations, coupled with radiation-induced solute segregation to these sinks. Therefore it is important to develop advanced predictive models for Mn-Ni-Si precipitation in F-M alloys under irradiation based on an understanding of the underlying mechanisms. Here we use a cluster dynamics model, which includes multiple effects of dislocations, to study the evolution of MNSPs in a commercial F-M alloy T91. The model predictions are calibrated by data from proton irradiation experiments at 400 {\deg}C. Radiation induced solute segregation at dislocations is evaluated by a continuum model that is integrated into the cluster dynamics simulations, including the effects of dislocations as heterogeneous nucleation sites. The result shows that MNSPs in T91 are primarily irradiation-induced and, in particular, both heterogeneous nucleation and radiation-induced segregation at dislocations are necessary to rationalize the experimental observations.