Thermodynamics of the iron-nitrogen system with vacancies. From first principles to applications

Abstract

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Nitrogen diffusion in vacancy-rich ferrite and austenite, from first principles to applications

“…There is evidence that this distinction between DFT and iron alloys in reality is significant when making thermodynamic predictions from first principles. For example, it has been shown that DFT-calculated nitrogen solubility's in iron have closer agreement with experimental data when excess vacancies [3] are introduced to idealised lattices. Furthermore, common processes encountered in industry; such as irradiation [4,5], quenching [6], ball milling and shot peening [7]; lead to deformed lattices which further increase nitrogen-vacancy interactions.…”

“…First principles data calculated as outlined in section 2.1 is used in combination with published data from [3] to calculate the jump rates for diffusion (see section 2.2.1) in BCC/FCC iron containing vacant lattice sites and interstitially dissolved nitrogen. Section 2.1 features only new/essential details regarding the DFT methodology applied, the reader is referred to the previously published work mentioned for more detailed discussion.…”

“…Section 2.1 features only new/essential details regarding the DFT methodology applied, the reader is referred to the previously published work mentioned for more detailed discussion. In particular, the energy barriers for nitrogen jumps in the proximity of a vacancy are quoted from [3] in table 2, which are needed to calculate the jump rates defined in equation 3. Using the calculated jump rates, an array of KMC trajectories are used to study the dynamics of the iron-vacancy-nitrogen system over the chosen temperature and nitrogen/vacancy concentration ranges.…”

“…Atomic Simulation Environment (ASE) [23] was used to interact with the GPAW software. The parameters which are chosen for each DFT calculation are adapted from previous work [3]. These are the kinetic cut-off energy for plane-wave functions, the number of k-points distributed in the Brillouin zone using the Monkhurst-Pack method [24], the supercell size, and the width of Methfessel-Paxton [25] (first order) smearing.…”

The Effects of Modifying the Activity of Nitriding Media by Diluting Ammonia with Nitrogen

“…The analysis of the equilibrium in the Fe-N system allows obtaining information regarding the phase composition of the nitrided layers obtained under strict conditions of temperature and nitrogen concentration in the furnace chamber atmosphere [ 1 , 2 , 3 , 4 , 5 ]. The adjustment of the nitrided layer phase composition can be set by altering the nitrogen potential of the atmospheres used: by maintaining it at the level of nitrogen solubility in a certain phase, one is able to control the phase composition of the layer [ 6 , 7 , 8 , 9 , 10 , 11 ].…”