Understanding the mechanical properties of reduced activation steels

TL;DR

This study uses density-functional theory to analyze the micro-mechanical properties of reduced activation ferritic/martensitic steels, revealing how alloying elements influence their elastic and ductile behavior for nuclear reactor applications.

Contribution

It provides a detailed ab initio analysis of how alloying elements affect the mechanical properties of RAFM steels, including lattice parameters, elastic moduli, and ductility.

Findings

V and W alloying enhance ductility.

Cr and Mn alloying increase brittleness.

Elastic properties depend linearly on alloy composition.

Abstract

Reduced activation ferritic/martensitic (RAFM) steels are structural materials with potential application in Generation-IV fission and fusion reactors. We use density-functional theory to scrutinize the micro-mechanical properties of the main alloy phases of three RAFM steels based on the body-centered cubic FeCrWVMn solid solution. We assess the lattice parameters and elastic properties of ferromagnetic $\alpha$-Fe and Fe$_{91}$Cr$_{9}$, which are the main building blocks of the RAFM steels, and present a detailed analysis of the calculated alloying effects of V, Cr, Mn, and W on the mechanical properties of Fe$_{91}$Cr$_{9}$. The composition dependence of the elastic parameters is decomposed into electronic and volumetric contributions and studied for alloying levels that cover the typical intervals in RAFM steels. A linear superposition of the individual solute effects on the properties of Fe$_{91}$Cr$_{9}$ is shown to provide an excellent approximation for the \emph{ab initio} values obtained for the RAFM steels. The intrinsic ductility is evaluated through Rice's phenomenological theory using the surface and unstable stacking fault energies, and the predictions are contrasted with those obtained by empirical criteria. Alloying with V or W is found to enhance the ductility, whereas additional Cr or Mn turns the RAFM base alloys more brittle.