Solid solution strengthening mechanism and interstitial diffusion behavior of rare earth element lanthanum in austenite using first-principles calculations

Abstract

Solid solution strengthening mechanism and interstitial diffusion behavior of RE element La in austenite (γ-Fe) were researched using first-principles calculation for improving the mechanical properties of austenitic stainless steel. The calculated results indicate that, for La atom solid solution γ-Fe, LaS γ-Fe shows the larger stability than LaOI γ-Fe and LaTI γ-Fe because of the smaller lattice distortion. LaOI γ-Fe and LaTI γ-Fe show the good plastic deformation capacity while LaS γ-Fe exhibits high brittleness because of the strong resistance to deformation and stiffness. Elastic anisotropy of LaOI γ-Fe is the strongest while that of LaS γ-Fe is the weakest, and the anisotropy is caused by the difference between the shear modulus G in xz plane and that in xy/yz planes. Fe–La chemical bonding in La atom solid solution γ-Fe is the typical metallic bonding but exhibits a certain degree of ionic characteristic, and the ionic characteristic of LaS γ-Fe is larger than that of LaOI γ-Fe and LaTI γ-Fe. Energy barrier for La atom diffuse between neighboring Oct sites is much larger than that between neighboring Tet sites, and from Oct site to Tet site in γ-Fe, which indicates that La atom diffuse between neighboring Oct sites is the most difficult. The reason is that, compared with Tet–Tet and Oct–Tet paths, the interaction between La atom at saddle point and the surrounding Fe atoms along Oct–Oct path is the strongest.