PLASMA NITRIDING OF AISI 5140 LOW ALLOY STEEL ASSISTED WITH HOLLOW CATHODE DISCHARGE AT LOW PRESSURE

Abstract

Plasma nitriding of AISI 5140 low alloy steel was carried at pressures ranging from 100[Formula: see text]Pa–500[Formula: see text]Pa for 4[Formula: see text]h with hollow cathode discharge assistance. The treated samples were characterized by optical microscope, microhardness tester, X-ray diffraction and electrochemical workstation. The results show that the compound layer is about 5[Formula: see text][Formula: see text]m in thickness and the depth of surface hardening layer is about 240[Formula: see text][Formula: see text]m for the sample nitrided at 100[Formula: see text]Pa for 4[Formula: see text]h. The hardness value of nitrided surface is about 830[Formula: see text]HV[Formula: see text], which is about 2.9 times higher than that (290[Formula: see text]HV[Formula: see text]) of the substrate. There is no obvious difference in the thickness of compound and diffusion layers, surface microhardness and phase composition of nitrided layers in comparison with that of samples nitrided at pressure 300 and 500[Formula: see text]Pa used by conventional plasma nitriding. But plasma nitriding with low pressure can effectively reduce the assumption of nitriding gas and amount of exhausted emission.