Surface Modification of Inconel 718 Superalloy by Plasma Immersion Ion Implantation

Abstract

Superalloy are alloys developed for elevated temperatures applications, where relatively severe mechanical stressing is found, and a high surface stability is frequently required. Improvements in the surface properties of a wide range of alloys have been obtained by the implantation of nitrogen while field test results for industrial tools and components from a diverse range of applications have been positive. The objective of this work is to improve the mechanical surface properties of Inconel 718 by PIII (Plasma Immersion Ion Implantation PIII). In these experiments, samples of Inconel 718 without heat treatment are used. Nitrogen ions in Inconel samples were implanted: a) for a period of one hour, and b) for a period of 3 hours. Tribological properties of PIII treated samples were compared with the ones for untreated samples are compared. The best result is obtained for the samples treated for 3 hours after 5000 cycles of an unlubricated pin-on-disk test, with very little wear. Introduction Nickel superalloys are part of a family of metallic materials that are used at elevated temperatures. Inconel 718 derives its strength from solid solutions of alloying elements and, to a large extent, from precipitates within a solid solution matrix. Superalloys maintain their good mechanical properties up to temperatures close to their melting points and present good resistance to oxidation. Among Ni-base superalloys, Inconel 718 is predominantly used in high temperature applications due to its highly satisfactory price/overall performance ratio, and good mechanical properties with excellent weldability [1, 2]. Gas turbine engines are the major applications of this alloy. However, its mechanical properties are degraded at temperatures above 650C [3-8]. Nitriding of superalloys has been less explored than nitriding of austenitic (FCC) stainless steels despite the similarity in structure and shortcomings (susceptibility to localized corrosion and poor tribological performance) for the two alloy systems [9, 10]. It is now well known that low temperature (<500°C) nitriding of austenitic stainless steels can produce a supersaturated FCC phase that combines high hardness and good corrosion resistance (above 500°C hardness is increased at the expense of corrosion resistance). This phase is known as s-phase or expanded austenite [11–13]. Due to the similarities between the austenitic