In order to take advantage of the individual advantages of plasma nitriding and plasma nitrocarburizing

and overcome their shortcomings

plasma complex treatment combining both plasma nitrocarburizing and plasma nitriding (hereinafter referred to as complex treatment) was developed and compared with a single plasma nitriding. The nitrided layer thickness

phase microstructure

cross-sectional microhardness were investigated by means of optical microscope

X–ray diffraction and microhardness tester. The results show that the compound layer thickness after complex treatment is much thicker than that after plasma nitriding

th

us the nitriding efficiency is improved remarkably. Fe

3

C phase was occurred in compound layer after complex treatment

and the dominated phase of the compound layer was transformed from γ′ to ε phase. Higher microhardness was obtained after a complex treatment. In addition

activation energy (Q) of forming compound layer decreases from 179.7 kJ/mol in plasma nitriding to 87.1 kJ/mol for the complex treatment. And the kinetics of plasma nitriding and complex treatment in the temperature range of 783 K to 843 K was obtained as the following formula d

plasma nitriding

=exp（15.8–10810/T）

 d

complex treatment

=exp（9.7–5237/T）.