Physics / Fizik

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

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Subject: search.filters.subject.Plasma nitriding

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  • Article
    Citation - WoS: 11
    Citation - Scopus: 13
    Magnetic Layer Formation on Plasma Nitrided Cocrmo Alloy
    (Elsevier Ltd., 2011) Öztürk, Orhan; Okur, Salih; Okur, Salih; Öztürk, Orhan; Riviere, Jean Paul; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of Technology
    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: 31
    Citation - Scopus: 40
    Structural and Magnetic Characterization of Plasma Ion Nitrided Layer on 316l Stainless Steel Alloy
    (Elsevier Ltd., 2009) Öztürk, Orhan; Okur, Salih; Öztürk, Orhan; Okur, Salih; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of Technology
    In this study, an FeCrNi alloy (316L stainless steel disc) was nitrided in a low-pressure R.F. plasma at 430 °C for 72 min under a gas mixture of 60% N2-40% H2. Structural, compositional and magnetic properties of the plasma nitrided layer was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and magnetic force microscopy (MFM). The magnetic behaviour of the nitrided layer was also investigated with a vibrating sample magnetometer (VSM). Combined X-ray diffraction, cross-sectional SEM, AFM and MFM, as well as VSM analyses provide strong evidence for the formation of the γN phase, [γN-(Fe, Cr, Ni)], with mainly ferromagnetic characteristics. The uniform nature of the γN layer is clearly demonstrated by the XRD, cross-sectional SEM and AFM analyses. Based on the AFM and SEM data, the thickness of the γN layer is found to be ∼6 μm. According to the MFM and VSM analyses, ferromagnetism in the γN layer is revealed by the observation of stripe domain structures and the hysteresis loops. The cross-sectional MFM results demonstrate the ferromagnetic γN phase distributed across the plasma nitrided layer. The MFM images show variation in the size and form of the magnetic domains from one grain to another.
  • Article
    Citation - WoS: 15
    Citation - Scopus: 15
    Microstructural, Mechanical, and Corrosion Characterization of Plasma-Nitrided Plastic Injection Mould Steel
    (Elsevier Ltd., 2005) Öztürk, Orhan; Onmuş, Ortaç; Öztürk, Orhan; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of Technology
    Plasma nitriding can be used to improve wear and corrosion behaviour of moulds for plastic injection by modifying the near-surface layers of these materials. In this study, a ferritic stainless steel (X36CrMo17) was plasma nitrided at 520-540 °C for 15-18 h under various gas mixtures of N2+H2 in an industrial nitriding facility. The nitrided layer microstructures, thicknesses, and strengths were studied by X-ray diffraction (XRD), conversion electron and X-ray Mössbauer spectroscopies (CEMS and CXMS), cross-sectional scanning electron microscopy (SEM), and cross-sectional nanohardness measurements. The corrosion behaviour was investigated by a salt spray method. Combined Mössbauer, XRD, and SEM analyses demonstrate that (Fe,Cr,Mn)-nitrides, the ε- and γ′-nitrides, the Fe3C-like carbide, and CrN are distributed in the top nitrided layers of several micron thickness. The CEMS and CXMS analyses clearly show the nearly complete decomposition of the surface and deeper layers into phase separated mixtures of pure bcc-Fe, (Fe,Cr,Mn)-nitrides, and CrN. The nitriding conditions with the gas composition N2/H2=1 produces the thickest nitrided layer (∼135 μm) with enhanced corrosion protection. The nanohardness of the surface layers is found to be plateau-shaped and increased by about a factor of three in comparison to that of the substrate material.