Modelling materials irradiation using the creation relaxation algorithm

Congratulations to my collaborator Ian Chesser at LANL for the publication of Structure and migration of heavily irradiated grain boundaries and dislocations in Ni in the athermal limit, I. Chesser et al, Phys. Rev. Mater. 8, 093606 (2024). This work employs the creation relaxation algorithm (CRA) to study the athermal irradiation response of grain boundaries and isolated dislocations, finding that these topological defects can be remarkably resistant to radiation.

Understanding how a material responds to an intense radiation environment is a problem of fundamental importance when wanting to build safe and reliable fusion power reactor. Metallic components exposed to the neutron fluxes of a Tokamak plasma undergo significant changes to their microstructure, which usually involve swelling that leads to large and possibly heterogeneous internal stresses. Such stresses can adversely affect a material component within the reactor, leading ultimately to failure.

The exposure of a material to a radiation environment is a multi-scale modelling problem in both time and space. Traditional finite temperature atomistic simulations have provided insight into the very earliest stages of irradiation, however it is unable to model directly the microstrucural evolution over a component's lifetime. To do this, other (coarser grained) modelling strategies are needed.

Many modelling approaches begin from the dilute defect limit of a perfect crystal, where microstructural fluctation timescales are faster than the timescale between cascades. However complex microstructures, involving for example, system-spanning connected dislocation structures have fluctuation timescales significantly longer than that of the irradiation time-scale. In this regime, microstructure does not change in a statistcally meaningful way between irradiation events, motivating an alternative modelling strategy starting from this premise. Indeed, the limiting form of this perspective is entirely absent of thermally activated structural evolution, being athermal and therefore naturally at zero temperature. Under these circumstances microstructure can only be driven through internal stress fluctuations due to the irradiation, with the dose-rate becoming effectively infinite. The CRA method is a simple realization of such an approach, producing a system spanning microstructure whose statistical properties in many cases converge to a steady state structure giving a new perspective from which to study the effects of temperature. The general CRA approach was developed in conjunction with my long term collaborator Sergei Dudarev at CCFE. For more details see our papers, Microscopic structure of a heavily irradiated material, P. M. Derlet and S. L. Dudarev, Phys. Rev. Mater. 4, 023605 (2020) and also Observation of Transient and Asymptotic Driven Structural States of Tungsten Exposed to Radiation, D. Mason et al, Phys. Rev. Lett. 125, 225503 (2020) which demonstrates how the CRA approach can lead to qualitative predictions that agree with experimental trends.

Well done Ian!