Compositional effects on ideal shear strength in Fe-Cr alloys

Abstract

The ideal shear strength is the minimum stress needed to plastically deform a defect free crystal; it is of engineering interest since it sets the upper bound of the strength of a real crystal and connects to the nucleation of dislocations. In this study, we have employed spin-polarized density functional theory to calculate the ideal shear strength, elastic constants and various moduli of body centered cubic Fe-Cr alloys. We have determined the magnetic ground state of the Fe-Cr solid solutions, and noticed that calculations without the correct magnetic ground state would lead to incorrect results of the lattice and elastic constants. We have determined the ideal shear strength along the 〈111〉{110} and 〈111〉{112} slip systems and established the relationship between alloy composition and mechanical properties. We observe strengthening in the 〈111〉{110} system as a function of chromium composition, while there is no change in strength in the 〈111〉{112} system. The observed differences can be explained by the response of the magnetic moments as a function of applied strain. This study provides insights on how electronic and magnetic interaction of constituent alloying elements may influence the properties of the resulting alloys and their dependence on alloy compositions.