A first-principles investigation on the effects of magnetism on the Bain transformation of $\alpha$-phase FeNi systems

TL;DR

This study uses first-principles calculations to explore how magnetism influences the Bain transformation in FeNi alloys, revealing that magnetic states significantly affect elastic properties and stability.

Contribution

It provides a detailed first-principles analysis of the magnetic effects on the Bain transformation in FeNi systems, highlighting the importance of magnetism in their elastic and structural stability.

Findings

Ni increases lattice constant in ferromagnetic states

Ni enhances shear and Young's moduli in bcc Fe

NiFe alloys are elastically unstable in nonmagnetic states

Abstract

The effects of magnetism on the Bain transformation of $\alpha$-phase FeNi systems are investigated by using the full potential linearized augmented plane wave (FLAPW) method based on the generalized gradient approximation (GGA). We found that Ni impurity in bcc Fe increases the lattice constant in ferromagnetic (FM) states, but not in the nonmagnetic (NM) states. The shear modulus $G$ and Young's modulus $E$ of bcc Fe are also increased by raising the concentration of nickel. All the compositions considered show high shear anisotropy and the ratio of the bulk to shear modulus is greater than 1.75 implying ductility. The mean sound velocities in the $[100]$ directions are greater than in the $[110]$ directions. The Bain transformation, which is a component of martensitic transformation, has also been studied to reveal that Ni$_{x}$Fe$_{1-x}$ alloys are elastically unstable in the NM states, but not so in the FM states. The electronic structures explain these results in terms of the density of states at the Fermi level. It is evident that magnetism cannot be neglected when dealing with the Bain transformation in iron and its alloys.