A STUDY OF IRON NITROGENATION BY HOT ISOSTATIC PRESSING

In this study a hot isostatic pressing (HIP) furnace under high temper ature and high nitrogen pressure is used to perform nitrogen diffusion in mechanically processed iron powders. After hipping, the gamma'-Fe4 N phase is formed while unreacted b.c.c. iron also remains in the powd er. The amount of gamma'-Fe4N is estimated by calculating the relative X-ray diffraction peak intensity. The latter amount increases with in creasing milling time because of new surface formation and defect crea tion. The nitrogen diffusion into grains occurs for a minimum value of the HIP pressure, then the alloying of nitrogen with iron appears for a minimum temperature. Mossbauer and EXAFS analyses indicate that the iron nitride is mainly located at the surface of the powder grains. ( C) 1998 Elsevier Science S.A.