عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Plasma nitriding is a thermochemical process that is used for surface hardening of many industrial steel components. In this study, hot work tool steel samples were plasma nitrided at 450, 500 and 550 oC temperatures, for 2.5,5,7.5 and 10 hours in a 75%N2-25%H2 gas atmospheve inside a pulsed DC vessel in order to determine the growth mechanism of surface layers. Diffusion zone, compound layer and surface morphology were studied by using optical and scanning electron microscopes. The phases formed in the nitriding process were determined by XRD method. In addition, the microhardness changes from surface to the centre of the samples were measured. Results showed that nitrogen has diffused in the substrate material via grain boundary diffusion mechanism.The surface hardness and the depth of hardened layer increased with an increase in the nitriding temperature and time. Moreover, the thickness of the compound layer increased by increasing the temperature and time. It seems that the radius of nitride particles on the surface is direethy related to the processing time. By increasing the nitriding temperature and time, surface morphology was changed and the radius of nitride particles on the surface also increased.