The Effect of Frequency and Duty Cycle Plasma Nitriding on the Surface Characteristics of Hot Work Steel AISI H13

In this research، the effects of plasma nitriding parameters including frequency and duty cycle investigated on samples with different grooves. Sample assemblies consisting of rectangular grooved steel blocks with groove dimensions of 2، 4، 6، 8 and 10 (T) ×40 (H) ×20 (L) and DIN/2344 steel plate (substrates) with dimensions of 30×40×60، then were prepared the sample assemblies were nitrided under the atmosphere content of 75%H2-25%N2، at temperature of 500 c، duty cycles of 40%، 60% and 80% and with frequencies of 8 and 10 kHz for 5 hours. Then the property of grooves surfaces investigate by experiments of the SEM، XRD، Roughness and Micro Hardness measurement. The results of the experiments showed that the surface of the plasma nitriding samples are covered by cauliflower form of particles that formation of this particles in plasma nitriding samples are due to sputtering of the surface during the process. With increasing thickness of the groove، frequency and duty cycle، roughness of surfaces raise. Also micro hardness rise with increasing the thickness of the groove and duty cycle resulting from the increase in percent of deposition particle nitride.. Hollow cathode phenomena occurred in sample with 2mm groove and 80% duty cycle in CPN. This will result in over heating of the sample which leads to a decrease hardness of the surface and an increasing in the Roughness of the surface. Also the results of the experiments XRD showed that، in the surface all of the samples form of γ΄: Fe4N and ε: Fe2-3N phases which proportion of ε to γ΄ increased by decreases duty cycle and increase the groove width.