Interfacial Segregation of Nitrogen in Iron

Abstract

AbstractThe absolute surface energy of pure δ-iron as a function of nitrogen content within the solidsolubility range has been measured. The surface energy is significantly reduced, showing that nitrogen is surface-active. The temperature-dependence of the surface energy of Fe-0.01 % N is positive and equal to 1.1 erg/cm2/degC. At saturation coverage of the surface, there is 0.7 ± 0.2 atom of nitrogen per surface atom of iron, with an estimated mean binding energy of 53 ± 5 kcal/mole. The binding energy of nitrogen to grain boundaries is 21 ± 3 kcal/mole. The results are discussed with reference to the contribution of grain boundaries to the total nitrogen solubility in iron and the relevance of grain-boundary adsorption to the intergranular fracture strength.