Plasma Processing of Iron Alloys-(II) Plasma Nitriding of an Austenitic Iron (Fe-18Cr-9Ni) Alloy

Abstract

To discuss plasma nitriding process as a kind of preparing process of functional gradient material, various characteristics of the layers nitrided by plasma of a mixed gas of nitrogen and hydrogen were studied. Fe-18Cr-9Ni alloy was nitrided at the range of temperature from 723 to 823 K for various periods (3.6 ks to 108 ks), and then each specimen was immediately quenched into iced water. Microstructural observa-tion, x-ray diffraction examination, measurement of hardness, EPMA analysis of nitro-gen, chromium, nickel, and iron, and chemical analysis of the surface layer of sepci-men were conducted. TEN observation of extracted CrN particles was also carried out to determine their mean diameter. The main results are as the follows: (1) The plasma nitriding is available for preparing FGM. (2) The profile of dissolved nitrogen in the nitriding layer, in which CrN was precipitated, decreased continueously from the specimen surface to the nitriding front. (3) The nitrogen is dissolved to 1.73wt% at 823 K. This nitrogen content is equal to about 10 times of the reported values. (4) The mean size of the CrN particle is 7nm in diameter.