Öztürk, OrhanOkur, SalihPichon, L.Liedke, M. O.Riviere, Jean Paul2017-03-082017-03-082011Öztürk, O., Okur, S., Pichon, L., Liedke, M.O., and Riviere, J.P. (2011). Magnetic layer formation on plasma nitrided CoCrMo alloy. Surface and Coatings Technology, 205(SUPPL. 2), S280-S285. doi:10.1016/j.surfcoat.2011.01.0470257-8972http://doi.org/10.1016/j.surfcoat.2011.01.047https://hdl.handle.net/11147/5004In 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 20h 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 (~30at.%). 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.eninfo:eu-repo/semantics/openAccessCoCrMo alloyExpanded austenite structureFerromagnetismPlasma nitridingMagnetoplasmaArticle2-s2.0-7995979192610.1016/j.surfcoat.2011.01.047