Influence of molybdenum addition on phase evolution of mechanically alloyed Fe _(84−x) Cr ₁₆ Mo _x (x=0, 1.5, 3 wt.%) alloys

The influence of molybdenum percentage on the phase evolution, solid solution formation, and microstructural refinement in high-energy mechanically alloyed Fe(84−x)Cr16Mox (x = 0, 1.5, and 3 wt.%) ferritic alloys was investigated. Elemental powders of Fe, Cr, and Mo were mechanically alloyed for 20 h and characterised using X-ray diffraction and Williamson – Hall analysis. Thermal stability was evaluated by using the powders obtained after each milling step, which were heat treated at 800 °C for 1 h in an argon atmosphere. XRD results revealed that a supersaturated single-phase BCC ferritic solid solution formed after 5 h of milling due to progressive dissolution of Cr and Mo into the Fe matrix. The average crystallite size decreased from 125–155 nm in the unmilled powders to 10–15 nm after 10 h of milling, while lattice strain increased to approximately 0.311% because of severe plastic deformation and defect accumulation. Increasing Mo content promoted lattice expansion, higher strain accumulation, and an increase in theoretical density from 7.79 to 7.97 g/cm³. Heat treatment reduced residual strain by 75–85% while preserving the BCC solid-solution structure. Therefore, this study highlighted the feasibility of producing thermally stable nanocrystalline Fe–Cr–Mo ferritic alloys through mechanical alloying.