Plasticity in irradiated FeCrAl nanopillars investigated using discrete dislocation dynamics

TL;DR

This study combines discrete dislocation dynamics simulations and TEM in situ tensile tests to analyze how irradiation-induced defects and composition fluctuations influence the plasticity and hardening behavior of FeCrAl nanopillars, revealing complex superposition effects.

Contribution

It introduces a detailed simulation and experimental analysis of the interplay between irradiation defects and composition inhomogeneity in irradiated FeCrAl alloys, highlighting a destructive interference in hardening contributions.

Findings

Irradiated alloys show higher yield strength and hardening.

Superposition of hardening effects can be destructive, reducing overall strength.

Experimental and simulation results agree on the destructive interference phenomenon.

Abstract

In this paper, we investigate plasticity in irradiated FeCrAl nanopillars using discrete dislocation dynamics simulations (DDD), with comparisons to transmission electron microscopic (TEM) in situ tensile tests of ion and neutron irradiated commercial FeCrAl alloy C35M. The effects of irradiation-induced defects, such as a/2 111 and a 100 type loops and composition fluctuations representative of phase separation in irradiated FeCrAl alloys, are investigated separately as well as superposed together in simulations. We explore the effects of defects on the stress-strain behavior, specifically yield strength and hardening response, of FeCrAl nanopillars. Our simulations confirm the widely accepted fact that irradiated alloys exhibit a stress-strain response with higher yield strength and hardening as compared to homogeneous alloys. However, our DDD calculations reveal an atypical superposition of the hardening contributions due to composition inhomogeneity and irradiation loops wherein hardening due composition inhomogeneity counteracts hardening due to irradiation loops at small scales. As a result, we observe that the yield strength in irradiated alloys, after taking into consideration the effects of both composition inhomogeneity and irradiation loops, is smaller than the yield strength of the alloys with only irradiation loops and is approximately same for the alloy with composition inhomogeneity alone. We identify this destructive interference in the superposition in our parallel TEM in situ tensile tests on unirradiated, ion irradiated, and neutron irradiated C35M FeCrAl alloy as well. This destructive interference in the hardening contributions contrasts with the widely utilized dispersed barrier hardening (DBH) models by the experimental community to model the hardening contributions due to different irradiation induced defects.