First-principles calculation of Fe-Mo-Cr alloys based on special quasi-random structure

Abstract

Mo element has an important effect on ferritic stainless steel. It is of great significance to study the role of the Mo element in the composition design of stainless steel alloys. In this paper, the formation energy, magnetic moment, electronic structure, mechanical and high-temperature mechanical properties of Fe-Mo binary alloys and Fe-Mo-Cr ternary alloys were obtained by density functional theory of first principles. The results showed that the formation energy increases gradually with the increase of Mo content. The alloys have a stable system when the Mo concentration is less than 3.125%. The addition of Cr increases the formation energy, but when Mo content is 3.125%, the formation energy is lower than that of Fe-Mo binary alloys. Fe atoms are ferromagnetic state and Mo atoms are anti-ferromagnetic state, there is an opposite magnetic effect between them. With the increase of Mo concentration, Mo atoms change from anti-ferromagnetic to paramagnetic. Mo atoms become paramagnetic when Mo concentration reaches 100%. Mo element has little effect on the shear modulus of the alloys. The hardness and compressive strength decrease with increasing Mo concentration. The addition of Cr atom also reduces the hardness. Fe-Mo alloys have better thermal stability when Mo concentration is 12.5%. The Cr atom significantly changes the thermodynamic properties of the alloys. The volume thermal expansion coefficient of Fe-Mo-Cr ternary alloys decreases with the increase of Mo concentration, and the highest temperature appears near the Mo concentration of 12.5∼18.75%.