Ž . Surface and Coatings Technology 138 2001 220228 Enhanced microhardness of four modern steels following nitrogen ion implantation a ´ a, b Manyuan Li , Emile J. Knystautas , Madhavarao Krishnadev a Departement de physique, Uni ersite Laal, Ste-Foy, Quebec, Canada G1K 7P4 ´ ´ ´ b Departement de mines et metallurgie, Uni ersite Laal, Ste-Foy, Quebec, Canada G1K 7P4 ´ ´ ´ ´ Received 13 June 2000; received in revised form 3 November 2000; accepted 10 November 2000 Abstract Ž . Ž . Samples of two kinds of hot-work steels Orvar Supreme, QRO 90 Supreme , one cold-work steel Sverker 21 and one Ž . Ž . ultra-high-strength aircraft steel AerMet 100 were implanted with 120 keV N ions 60 keVN at doses ranging from 2 5 10 15 to 1.2 10 17 ionscm 2 at room temperature. Also implanted into the four steels were 60 keV C ions using the same doses. The Knoop microhardnesses on the sample surfaces increased by 31 72% at load of 25 gf after nitrogen ion implantation. There was no obvious effect on microhardness after carbon ion implantation. Tribological properties of the nitrogen ion Ž 16 2 . implanted samples were evaluated. A heat-treatment study of nitrogen ion implanted 8 10 ionscm AerMet 100 and Sverker 21 showed that the hardness reduction arising from heat treatment was clearly lower for the implanted samples heat-treated at 400°C. The microhardness of the implanted layers alone was calculated by the Jonsson Hogmark model. The ¨ layer thickness used for the calculation of implanted-layer hardness was obtained from a molecular dynamic simulation code Ž . TRIM . The residual stress of the surface after nitrogen ion implantation was measured by X-ray diffraction. Friction and wear properties of the implanted samples were also measured. Nanohardness and Young’s modulus were measured for the nitrogen Ž . ion implanted layers. Grazing angle X-ray diffraction GXRD analysis shows the possible formation of nitride phases after Ž . nitrogen ion implantation. After nitrogen implantation, samples were depth profiled by AES Auger Electron Spectrometry to confirm the depth distribution of the implanted nitrogen ions. Implanted samples showed increased hardness, wear resistance and Ž . surface compressive stress. By using X-ray photoelectron spectroscopy XPS , Cr N phases were found in Orvar Supreme and 2 Ž . Sverker 21 samples implanted with nitrogen ions. These two steels have higher content of Cr 5.2% and 12% , and thus their hardness increase is greater than in the steels with lower Cr content. 2001 Elsevier Science B.V. All rights reserved. Ž . Ž . Ž . Ž . Ž . Ž . Keywords: B Knoop hardness test; B Pin on disc; B Scanning electron microscopy SEM ; B Photoelectron spectroscopy; C Ion Ž .Ž . implantation; X D Tool steel 1. Introduction Ion implantation has been extensively used for im- proving mechanical and tribological properties of metal surfaces 1,2 . Previous work on the implantation of Corresponding author. Tel.: 1-418-656-5569; fax: 1-418-656- 2040. Ž . E-mail addresses: mli@phy.ulaval.ca M. Li , ejknyst@phy.ulaval.ca Ž . Ž E.J. Knystautas , Madhavarao.Krishnadev@gmn.ulaval.ca M. Krish- . nadev . nitrogen and other types of ions into some steels has shown improvement in mechanical and tribological properties, notably the hardness, which is related to the abrasive wear resistance. Early uses of ion implantation for improving the surface hardness started in the early 1970s. They were carried out in either pure iron or Ž steel with carbon, nitrogen, or inert gas ion beams e.g. .  Ar 3 . The hardening can be related either to the Ž . formation of carbides nitrides or to radiation-induced dislocation effects 4,5 . Along with the other surface hardening processes, such as coating, nitriding, PVD 0257-897201$ - see front matter 2001 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 2 5 7 - 8 9 7 2 00 01154-3