Physics / Fizik

Permanent URI for this collectionhttps://hdl.handle.net/11147/6

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Author: search.filters.author.Pichon, L.Publisher: search.filters.publisher.Elsevier Ltd.

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  • Article
    Citation - WoS: 2
    Citation - Scopus: 3
    Use of Combination of Accelerator-Based Ion-Beam Analysis Techniques To the Investigation of the Corrosion Behavior of Cocrmo Alloy
    (Elsevier Ltd., 2014) Noli, F.; Misaelides, P.; Lagoyannis, A.; Pichon, L.; Öztürk, Orhan
    Nuclear Reaction Analysis - NRA in combination with d-RBS (Ed: 1.35 MeV) was applied in order to investigate the corrosion behavior of CoCrMo alloy. The corrosion resistance of the alloy was compared to that of modified CoCrMo samples by several techniques as plasma nitriding and oxidizing at moderate temperature (∼400 °C). Electrochemical techniques in simulated body fluid 0.9% NaCl (37 °C) were applied in order to accelerate the corrosion process. The nitrogen depth distribution before and after the corrosion was determined using the 14N(d,α)12C and the 14N(d,p)15N nuclear reactions whereas the oxygen by the 16O(d,p)17O. The surface morphology and microstructure was investigated using microscopy techniques. It was found that surface treatments produce thick nitrided layers (5-6 μm) consisting of a supersaturated nitrogen solution (nitrogen concentration is ∼30 at.%) in the matrix (expanded phase γN) and a thin oxygen solution (0.3 μm). The samples subjected to plasma nitridation and oxidation exhibited the lowest deterioration and better resistance to corrosion compared to the single nitrided or single oxidized and the untreated material. This could be attributed to the modified surface region with the high nitrogen content and the presence of oxygen.
  • Article
    Citation - WoS: 11
    Citation - Scopus: 13
    Magnetic Layer Formation on Plasma Nitrided Cocrmo Alloy
    (Elsevier Ltd., 2011) Öztürk, Orhan; Okur, Salih; Pichon, L.; Liedke, M. O.; Riviere, Jean Paul
    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 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.
  • Article
    Citation - WoS: 26
    Citation - Scopus: 24
    Cocrmo Alloy Treated by Floating Potential Plasma Assisted Nitriding and Plasma Based Ion Implantation: Influence of the Hydrogen Content and of the Ion Energy on the Nitrogen Incorporation
    (Elsevier Ltd., 2010) Pichon, L.; Okur, Salih; Öztürk, Orhan; Rivière, J. P.; Drouet, M.
    Nitriding was performed on a medical grade CoCrMo alloy at 400°C in N2 or N2-H2 atmosphere at a working pressure of 0.84Pa for 2h. Various surface treatment techniques were used to incorporate nitrogen into the CoCrMo alloy: without any plasma assistance, by floating potential radio-frequency plasma assisted nitriding (FPPAN), by plasma based ion implantation (PBII) with several high voltage accelerations (up to 20kV). Without plasma activation, no nitrogen is incorporated in the CoCrMo. On the contrary, all the plasma or PBII treated samples show the formation of a nitrogen-rich f.c.c. γN phase. The layer nitrided over few microns has a nitrogen composition ranging from 30at.% to about 20at.% near the nitrided layer-substrate interface, with an enhanced surface microhardness. Hydrogen is found to enhance the nitriding efficiency. Without hydrogen, a high voltage polarization provides a supplementary amount of implanted nitrogen available for further diffusion and the sputtering of the surface passive oxide. So, with limited high voltages, thicker layers with higher amounts of nitrogen can be achieved by PBII compared to plasma nitriding. However, with higher voltages, the sputtering becomes too important and the nitride layer is thinner. © 2010 Elsevier B.V.