Thermodynamic stability of iron nitrides at temperatures below 350 °C

Although iron nitride coatings are applied for their good tribological properties, their thermodynamic stabilities are unknown in the temperature range in which they are used. We have investigated the {ε} and {γ}' nitride phases between 0 and 350 ^∘{}C with ion implantation and find evidence that while the {ε}-Fe₂{N}_{1{{-}}x}with x≥2/3 is stable, γ'-{Fe}₄N is not. At T≤150 ^∘C, ion irradiation converts γ-{Fe}₄N into ε-{Fe}₂N_1-x, with x=0.5. This {ε} nitride can then be transformed back into {γ}'-Fe₄N by annealing at temperatures of 150 ^∘{}C and higher. Ion irradiation assists this process as well.