Geometric effect of ion nitriding on the nitride growth behavior in hollow tube

The growth behavior of the nitride layer inside a long hollow tube with an intricate geometry was studied to find a way to enhance the uniformity of the nitride layer. The inner surface of steel tube of 30- mm inner diameter was machined to have corrugation depths ranging from 0.65 to 3.90 mm and corrugation widths from 1.10 to 13.2 mm. After the specimens were ion nitrided at 525 ° for 10 hr in 2.5 torr operating pressure, the thickness of the compound layer and the diffusion layer on the land and the groove was measured and analyzed according to corrugation depth and width. As the corrugation becomes deeper, the thickness of the compound layer on the land increases and that of the layer on the groove decreases. The thickness of the diffusion layer on the land and the groove depicts a similar tendency to that of the compound layer. As the corrugation becomes wider, the compound layer thickness on the land decreases and that of the layer on the groove increases to the contrary. Thickness variations in the diffusion layer on the land and the groove resemble those of the compound layer. The nitride growth characteristics on the corrugated geometry in ion nitriding was discussed in view of Hollow Cathode Discharge (HCD) effect, nitrogen concentration, and the probability of compound adsorption.