Plasma source nitriding

Abstract A new method of surface nitriding, called “plasma source nitriding”, has been developed. This method is different from “ion nitriding” in the following respects: (1) the function of nitrogen- and hydrogen-ion bombardment of a workpiece is independent of the function of plasma production, (2) a homogeneity of nitriding depth is obtainable even if the geometrical shape of the workpiece is complicated, (3) the cost of nitriding gases is reduced due to the lower operating gas pressure which is of the order of 10 -4 Torr in the vacuum vessel, and (4) there is no trouble of arcing between workpieces and plasma. On the basis of the experimental results, the activation energy for nitrogen diffusion in 316 stainless steel by this method was calculated to be about 3.9 kcal/mol. This value was remarkably small compared to the value of 17.3 kcal/mol in 304 stainless steel by ion nitriding. The nitriding time was about 3 h by the new method and 15 h by ion nitriding to get a hardened depth of 27 μm in 316 stainless steel; the nitriding time was shortened to one-fifth.