First-Principles Investigation of the Effect of Alloying Elements on Stacking Fault Energy and Deformation Mechanisms in FCC Steels for Nigerian Manufacturing

This study presents a first-principles computational investigation of the influence of alloying elements including Mn, Ni, Cr, Si, and N on stacking fault energy (SFE) in face-centred cubic iron alloys, and the implications for deformation twinning versus dislocation glide mechanisms in TWIP and TRIP steels relevant to Nigerian automotive and defence manufacturing needs. Stacking fault energy is the fundamental thermodynamic parameter governing whether FCC steels deform by twinning-induced plasticity or transformation-induced plasticity, and accurate first-principles SFE calculations provide the most reliable approach for alloy design in this family. Density functional theory calculations are performed using the Vienna Ab Initio Simulation Package (VASP) with the PBE-GGA exchange-correlation functional on supercell models containing systematic substitutional alloying element concentrations. The generalised stacking fault energy surface (GSFE) is calculated and the intrinsic and unstable stacking fault energies extracted. The effect of short-range chemical ordering on SFE is assessed through special quasi-random structures. SFE values are used to predict the deformation mode transition from TRIP to TWIP to perfect dislocation glide as a function of alloy composition. Model predictions are compared with experimental deformation substructure observations by TEM on alloy compositions synthesised and deformed at the study institution. The study provides an original first-principles alloying guidance framework for TWIP-TRIP steel design. Keywords: stacking fault energy, first-principles, TWIP steel, alloying, deformation mechanism.