Duplex Surface Modification of M2 High-Speed Steel

In this investigation, a duplex surface modification of M2 high-speed steel (HSS) was demonstrated, including electron beam treatment (EBT) followed by a tungsten nitride (WN) coating deposition. The influence of the EBT of the substrate on the functional properties of the film was also studied. The phase composition of the EBT sample consists of Fe (the main element in the M2 HSS), as well as MC and M6C carbides, while the phase composition of the EBT + WN sample consists of the alpha'-Fe, M6C, and WN phases. The depth of the treated zone is about 20 mu m, and the thickness of the WN coating is about 300 nm in all cases. The hardness of the coating deposited on the EBT substrate is 12.4 GPa, while that of the WN film deposited on the untreated substrate is 8.8 GPa. The application of the electron beam treatment procedure and deposition of WN film leads to an improvement in the tribological properties where the coefficient of friction decreases from 0.81 to 0.66. However, the same coating deposited on untreated substrate exhibits even less friction coefficient values of 0.54. The applied modification technique suggests that this is a viable method for improving the mechanical and tribological properties of the surface of tool steels and, thus, their longevity and applicability.