Fine structure and interface structure of ion-bombardment nitrided layers

The fine structure and interlace structure of ion-nitrided layers in 35CrMo steel treated by ion-nitriding at 550 degrees C for 6 h were studied with a transmission electron microscope (TEM) and a high resolution transmission electron microscope (HRTEM). The results showed that the phase gamma'(Fe4N) is a compact structure of equi-axis fine grains. The outermost layer of ion-nitriding is phase epsilon and gamma', which are arranged in alternating, ribbon-like strips. There are abundant vacancy, dislocation, twin and stacking fault defects. Nitrogen atoms in gamma'(Fe4N) are distributed orderly. The interface between phase epsilon and phase gamma' is smooth and straight and coherent. Their orientation relationships are ( 1 (1) over bar 1)(gamma') //(0001), and [110](gamma') // [11 (2) over bar 0]epsilon. Not only the structure ledges of monoatom layer, but also those of multiatom layer were found on the interface of phase epsilon and phase gamma'. The existence of a number of crystal defects is the main reason why bombing of ions can accelerate the nitriding process.