Phase stability and magnetic properties in fcc Fe-Cr-Mn-Ni alloys from first-principles modeling

Abstract

Systematic investigation of phase stability of the magnetic fcc Fe-Cr-Mn-Ni system---promising candidate structural materials to replace conventional austenitic steels---has been performed using a combination of spin-polarized density-functional theory, cluster expansion, and Monte Carlo simulations. The developed model was able to reproduce all known ground states (GSs) in the studied system and to predict new ones with strongly negative formation enthalpy---ternary ${\mathrm{CrMnNi}}_{2}$ and quaternary ${\mathrm{FeCr}}_{2}{\mathrm{MnNi}}_{4}$. Investigation of phase stability was done at 0 K and finite temperatures in the whole concentration range and allowed us to observe the important role of Ni and Mn. Ni is the only element in the system that increases the order-disorder transition (ODT) temperature, which means that the fcc alloys with decreased concentration of Ni will form solid solutions at lower temperatures. Analysis of the effect of the addition of Mn to Fe-Cr-Ni alloy confirms a general trend of statistical correlation between the averaged magnitude of magnetic moments and volume per atom found from the predicted stable structures in the quaternary system and underlying subsystems. This linear magneto-volume relationship trend is, however, weaker in Fe-Cr-Mn-Ni alloys in comparison with those in the Fe-Cr-Ni system. Furthermore, Ni and Mn form the most stable GS---$\text{L}{1}_{0}$-MnNi, which has one of the strongest tendencies to segregate in fcc Fe-Cr-Mn-Ni alloys evidenced by the strength of Mn-Ni short-range ordering (SRO). Mn-Ni SRO significantly increases ODT temperature in the vicinity of $\text{L}{1}_{0}$-MnNi and to the equiatomic region. The ODT of ${\mathrm{Cr}}_{18}{\mathrm{Fe}}_{27}{\mathrm{Mn}}_{27}{\mathrm{Ni}}_{28}$ alloy is found to be $1290\ifmmode\pm\else\textpm\fi{}150$ K, which supports the experimental observation of the disordered solid solution structure in ${\mathrm{Cr}}_{18}{\mathrm{Fe}}_{27}{\mathrm{Mn}}_{27}{\mathrm{Ni}}_{28}$ alloy at higher temperatures.