First-principles study of bcc Fe-Cr-Si binary and ternary random alloys from special quasi-random structure

Using a combination of first-principles calculations with special quasi-random structure and quasi-harmonic approximation methods, we have calculated formation energy, magnetic moments, mechanical properties and thermodynamic properties of binary FeCr and ternary FeCrSi random alloys. The results agree well with available theoretical and experimental data. The body centered cubic structures and ferromagnetic phase are employed to calculate these properties in this work. The phase stability studies show that FeCr alloys are stable systems in Cr concentrations below 6% region. However, binary FeCr alloys are the systems with a miscibility gap for Cr concentrations above 6%. The ternary FeCrSi systems show much less formation energy than FeCr systems. For ternary FeCrSi alloys, Fe9Cr22Si1 shows maximum value of formation energy. Studies on magnetism have shown that Si is a kind of nonmagnetic material, it can be used to reduce magnetic moments of FeCr alloys. Doping a little Si into FeCr alloys can form more stable systems and improve bulk modulus, shear modulus and young's modulus in both low-Cr and rich-Cr concentration regions. Si element can generate effects on Debye temperature and volumetric thermal expansion coefficient of the alloy. But Si element can not generate obvious effects on constant volume heat capacity of FeCr alloys.