Orientation relations of nitrides in iron made by ion implantation

The texture of the ion nitrides α″, ε-Fe2N1-x and γ′-Fe4N produced by N implantation into single-crystal iron has been determined by X-ray diffraction. By using two different single-crystal orientations. (111) and (001), the influence of substrate orientation could be determined. In the (111) Fe single crystal the close-packed planes (CPPs) of the nitrides are always parallel to those CPPs of the iron which are perpendicular to the surface. In the (001) crystal the CPPs are almost but not exactly parallel to those CPPs of the iron which stik out from the surface plane. A similar behaviour is observed for the closed-packed directions (CPDs). The general observation for all nitrides is that CPPs and CPDs of the nitrides prefer to be parallel to CPPs and CPDs of the iron. In this way the interface energy is minimized. Furthermore, slip occurs most easily along the CPPs and CPDs. Slip is needed to accommodate the volume expansion caused by the nitride formation. Finally, implant temperature and implant direction have no influence on the texture of the ε-nitride. Knowing these relations, it is possible to control the texture of iron nitrides by choosing the appropriate Fe substrate.