New Method for Preparing Cubic Boron Nitride Hardened Layers

Hardened layers 0.15 - 0.2 mm thick were prepared by a duplex treatment combining boronising at a temperature of 900 ° C for 5 h and plasma immersion ion implantation with nitrogen ions at an implanting energy of 60 keV to a dose of 3×10¹⁷ atoms cm ^-2. at a temperature of 400°C on 50Mn steel (0.5C - 0.8Mn, wt-%) substrates. Cubic boron nitride, hexagonal boron nitride, B₂O₃, FeB, Fe₂B were found in the hardened layers by X-ray photoelectron spectroscopy and X-ray diffraction. The amount of c-BN phase dominates in the region from the surface of the hardened layers to a depth of 60 nm. The friction properties and hardness of the hardened layers were determined by standard sphere on disc sliding friction experiments at room temperature under unlubricated conditions and by Vickers microhardness experiments under different loads on duplex treated specimens and on the specimens treated alone by boronising. The results of the experiments showed that the duplex specimens of 50Mn steel had a far greater (up to 44 HV(0.1 N)) hardness and wear resistance than the specimens of 50Mn steel treated only by boronising.