Please use this identifier to cite or link to this item: http://hdl.handle.net/1959.3/231745

Title

Nitriding of austenitic stainless steel by plasma immersion ion implantation

Author(s)

Collins, G. A.;  Hutchings, R.;  Short, K. T.;  Tendys, J.;  Li, X.;  Samandi, M.

Abstract

Plasma immersion ion implantation (PI3 ™), in which the diffusion of nitrogen from a low pressure r.f. plasma is combined with the implantation of nitrogen ions at energies up to 45 kV, is an effective means of nitriding austenitic stainless steel. At temperatures up to 450 degrees Celsius, tribological properties can be improved without loss of corrosion resistance. In common with other nitriding processes in this temperature range, a supersaturated f.c.c. phase is formed, sometimes described as expanded austenite, which is maintained to very high nitrogen concentrations. At higher temperatures, chromium nitride is precipitated and the expanded austenite decomposes, leading to a reduction in corrosion resistance. Glancing-angle X-ray diffraction (XRD) of PI3-treated AISI 316 stainless steel at temperatures between 350 and 450 degrees Celsius suggests that a highly homogeneous layer of expanded austenite is produced. The expansion increases with increasing process time, but decomposition of the supersaturated phase occurs after several hours of treatment if the temperature is too close to 450 degrees Celsius . For a fixed process time, the expansion appears to be greatest at the lower temperatures (350 degrees Celsius), although it can also be influenced by other processing parameters such as plasma density. Microstructural examination by cross-sectional transmission electron microscopy (TEM) has challenged the identification of the supersaturated phase as expanded austenite and reveals the complexity of the modified layer not seen by glancing-angle XRD. Most striking is the formation of a thick (2-3 μm) amorphous zone which may contain nanocrystalline precipitates of CrN and α -ferrite. A highly defective layer (up to 2 μm thick) of expanded austenite has been observed to underlie the amorphous zone where nitrogen diffusion is facilitated by the high defect density. Only partial reconciliation of the TEM results with the XRD observations has been possible to date.

Publication type

Journal article

Source

Surface and Coatings Technology: incorporating the proceedings of the 4th International Conference on Plasma Surface Engineering, Garmisch-Partenkirchen, Germany, 19-23 September 1994 / L. Stals, K.-T. Rie, D. C. Schram and G. K. Wolf (eds.), Vol. 74-75, no. Part 1 (Sept 1995), pp. 417-424

Publication year

1995

FOR Code(s)

0204 Condensed Matter Physics;  0306 Physical Chemistry (Incl. Structural);  0912 Materials Engineering

Keyword(s)

Austenitic stainless steel;  Coatings;  Corrosion resistance;  Cross-section TEM;  Decomposition;  Diffusion;  Glancing-angle x ray diffraction;  Hard coatings;  Ion implantation;  Ion nitriding;  Microstructure;  Nitriding;  Plasma applications;  Plasma immersion ion implantation;  Plasma ion implantation;  Plasmas;  Transmission electron microscopy;  Tribology;  X ray diffraction

Publisher

Elsevier

ISSN

0257-8972

Publisher URL

http://dx.doi.org/10.1016/0257-8972(95)08370-7

Copyright

Copyright © 1995 Elsevier Science S.A.

Peer reviewed