Microwave Plasma Nitriding of Hollow Tube Inner Wall

Abstract

Microwave plasma nitriding at the internal wall surface of hollow tubes is described. Hollow tubes (1, 1.5, 2 and 3 mm inner diameter), with lengths of 5 and 12 mm were used for the investigation. Hardness values around 800 Hv were measured at both ends of the nitrided tubes for all diameters. The 3 mm inner diameter hollow tube had almost uniform internal wall hardness (above 700 Hv) along the entire tube length when subjected to microwave plasma nitriding at 773 K for 5 h in 50%N₂-50%H₂ mixing gas. A diffusion layer up to 0.6 mm was formed and compound layer of ε-Fe_2-3N and γ′-Fe₄N was precipitated at the internal surface of the tube. The effective nitriding depth of the microwave plasma inside the 2 and 3 mm diameter tubes were 3 times the diameter of the hollow tube.