Nitriding of AISI M2 tool steel in an inductive r.f. plasma

The nitriding of AISI M2 tool steel in an inductive r.f. plasma was investigated. The plasma was sustained with a 27.12 MHz generator in gas mixtures of N₂ and H₂ at a pressure of 10 mbar. The ion nitriding was performed at a net r.f. power of 400 W at substrate temperatures of 450-500 °C. X-ray diffraction studies of the treated samples revealed that the most efficient formation of nitride phases was observed in samples nitrided in a pure N₂ plasma. As a result of the ion nitriding the surface hardness was substantially increased from a Vickers hardness VHN of 290 kgf mm^-2 for untreated samples to a maximum VHN of 1200 kgf mm^-2 for samples treated in a plasma sustained in a gas mixture with N₂:H₂ = 1:1.