α”-Fe16N2 is a promising environmentally-friendly rare-earth-free permanent magnet material with ultra-high saturation magnetization. Recent research has demonstrated experimentally through a thermally quenching treatment using γ’ phase Fe4N as a precursor to synthesize α”-Fe16N2 in bulk format. In this research, we investigated γ’-Fe4N thin film thermal decomposition process and potential localized phase transition from fcc phase to bct phase using Molecular Dynamics (MD) simulation method. As nitrogen concentration is much higher in γ’-Fe4N (5.9 wt.%) than that in α’-Fe8N or α’’-Fe16N2 (3 wt.%), Nitrogen “depletion” process must have to occur during the thermal decomposition to form possible lower-Nitrogen content bct Fe-N solid solution. A localized “Nitrogen-rich” grain boundary lattice defect model is designed to induce Nitrogen bond forming through the recombination of nitrogen pair atoms, and therefore significantly improves local reduction of Nitrogen content in the α’-Fe4N lattice sample during thermal treatment. Modified Embedded Atom Method (MEAM) interatomic potential of Fe-N system is applied. Bond forming/breaking and local Nitrogen displacement analysis (MSD) are also performed in the thermostat-controlled heating/quenching simulation process. We use virtual XRD method and formation energy calculation to assess and detect the new material phases on the thermally-treated and energy minimized lattice sample.
1 Jian-Ping Wang, “Environment-friendly bulk Fe16N2 permanent magnet: Review and Prospective”, Journal of Magnetism and Magnetic Materials, 497(2020) 165962
2 J. Zhu, G, Guo and J.-P. Wang, "Study of γ'-F4N Annealing Process Through Molecular Dynamics Modeling", TMS 2022 151st Annual Meeting, The Minerals, Metals & Materials Series, Page 109-117, https://doi.org/10.1007/978-3-030-92381-5_11
3 M.H. Wetzel, M.R. Schwarz, A. Leineweber, High-pressure high-temperature study of the pressure induced decomposition of the iron nitride γ′-Fe4N, Journal of Alloys and Compounds, Volume 801, 2019, Pages 438-448