Fine structure and interface structure of ion-bombardment nitrided layers

The fine structure and interface structure of ion-nitrided layers in 35CrMo steel treated by ion-nitriding at 550°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 γ́ (Fe4N) is a compact structure of equi-axis fine grains. The outermost layer of ion-nitriding is phase ε and γ′, which are arranged in alternating, ribbon-like strips. There are abundant vacancy, dislocation, twin and stacking fault defects. Nitrogen atoms in γ′ (Fe4N) are distributed orderly. The interface between phase ε and phase γ′ is smooth and straight and coherent. Their orientation relationships are (1 11)γ′∥ // (0001)ε and [110]γ′; // [11 20]ε. Not only the structure ledges of monoatom layer, but also those of multiatom layer were found on the interface of phase ε and phase γ′. The existence of a number of crystal defects is the main reason why bombing of ions can accelerate the nitriding process.