Promotion of nitriding in surface layers of metals by preparative irradiation of REB

Various nitriding methods have been popularly used to make hard in surface layers of pure-irons, but it has taken a long processing time to obtain thick nitriding layers. In order to reduce this processing time, we tried irradiation of REB to a metal before it was processed by a nitrogen plasma. By this irradiation, many defections are formed in the metal. Along these defections nitrogen ions penetrate fast, and form thicker nitriding layers. Irradiation of REB to a metal piece was made with a modified Pulserad 110A. The energy, the pulse width and the current density of REB were 1.4 MeV, 30 ns and 200 A/cm², respectively. After a shot, the piece was processed with a nitrogen plasma. In the case of the pure-iron, the maximum thickness of γ′-phase layers (Fe4N) was 40 µm, and this value was 1.5 times longer than that obtained without pre-irradiation.