Magnetic layer formation on plasma nitrided CoCrMo alloy |
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| Authors: | O Öztürk S Okur L Pichon MO Liedke JP Riviere |
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| Affiliation: | 1. Department of Physics, Izmir Institute of Technology, Urla 35430, Izmir, Turkey;2. Institute PPRIME UPR3346 CNRS, ENSMA, Universite de Poitiers, Futuroscope-Chasseneuil, France;3. Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf, P.O. Box 510119, D-01314 Dresden, Germany;1. State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing, 210016, China;2. State Key Laboratory for Mechanical Behavior of Materials, Xi''an Jiaotong University, Xi''an, 710049 China;3. Center of Super-Diamond and Advanced Films (COSDAF), Department of Physics & Materials Science, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong, China;4. Advanced Coatings Applied Research Laboratory, Department of Mechanical and Biomedical Engineering, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong, China;1. RCPTM, Joint Laboratory of Optics of Palacky University and Institute of Physics of Academy of Science of the Czech Republic, Faculty of Science, Palacky University, 17. listopadu 12, 771 46 Olomouc, Czech Republic;2. Department of Optics, Faculty of Science, Palacky University, 17. listopadu 12, 771 46 Olomouc, Czech Republic;1. Institute of Nuclear Sciences, Hacettepe University, Beytepe, 06800 Ankara, Turkey;2. Center for Solar Energy Research and Applications (GÜNAM), Middle East Technical University, Dumlup?nar Blvd. 1, 06800 Ankara, Turkey;3. Physics Department, Middle East Technical University, Dumlup?nar Blvd. 1, 06800 Ankara, Turkey;4. DFG-Centre for Functional Nanostructures, Karlsruhe Institute of Technology, Wolfgang Gaede Str. 1, 76131 Karlsruhe, Germany;5. Micro and Nanotechnology Program, Middle East Technical University, Dumlup?nar Blvd. 1, 06800 Ankara, Turkey;6. Department of Physics, Koç University, 34450 ?stanbul, Sar?yer, Turkey;7. CNR-IOM, Area Science Park, 34149 Trieste, Italy;8. Graduate School of Nanotechnology, Department of Physics, University of Trieste, 34127 Trieste, Italy;9. Department of Chemical Engineering and Biotechnology, University of Cambridge, Pembroke Street, Cambridge CB2 3RA, United Kingdom;10. CBM S.c.r.l., Area Science Park, Basovizza, 34149 Trieste, Italy;1. CEA, LIST, CEA Saclay, Gif-sur-Yvette, F-91191, France;2. CEIT and Tecnun (University of Navarra), Manuel de Lardizábal 15, 20018, San Sebastián, Basque Country, Spain |
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| Abstract: | In this study structural and magnetic character of the expanded austenite phase (γN) layer formed on a medical grade CoCrMo alloy by a low-pressure Radio-Frequency plasma nitriding process was investigated. The formation of the expanded austenite phase is facilitated at a substrate temperature near 400 °C for 1, 2, 4, 6 and 20 h under a gas mixture of 60% N2–40% H2. The magnetic state of the γN layers was determined by a surface sensitive technique, magneto-optic Kerr effect (MOKE), and with a scanning probe microscope in magnetic force mode (MFM). Strong evidence for the ferromagnetic nature of the γN-(Co,Cr,Mo) phase is provided by the observation of stripe domain structures and the hysteresis loops. The ferromagnetic state for the γN phase observed here is mainly linked to large lattice expansions (~ 10%) due to high N contents (~ 30 at.%). As an interstitial impurity, nitrogen dilates the host lattice i.e. the Co–Co (or Fe–Fe) distance is increased, which strongly influences the magnetic interactions. An analogy between the magnetic properties of the expanded phases, γN-(Fe,Cr,Ni) and γN-(Co,Cr,Mo), formed in austenitic stainless steel alloys and the CoCrMo alloy of this study is made, and it is suggested that the ferromagnetic states for the γN-(Co,Cr,Mo) and γN-(Fe,Cr,Ni) phases may be correlated with the volume dependence of the magnetic properties of fcc-Co/Co4N and fcc-Fe/Fe4N, respectively. |
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