Magnetic layer formation on plasma nitrided CoCrMo alloy

SURFACE & COATINGS TECHNOLOGY

卷:205

Article; Proceedings Paper

Ozturk, O.¹  Okur, S.¹  Pichon, L.²  Liedke, M. O.³  Riviere, J. P.² 

[1] Izmir Inst Technol, Dept Phys, TR-35430 Izmir, Turkey

[2] Univ Poitiers, ENSMA, CNRS, UPR3346,Inst PPRIME, Futuroscope, France

[3] Forschungszentrum Dresden Rossendorf, Inst Ion Beam Phys & Mat Res, D-01314 Dresden, Germany

关键词: CoCrMo alloy;    Expanded austenite structure;    Plasma nitriding;    Ferromagnetism;    MOKE;    MFM;   

DOI  :  10.1016/j.surfcoat.2011.01.047

来源: Elsevier

【 摘 要 】

In this study structural and magnetic character of the expanded austenite phase (gamma(N)) 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 degrees C for 1, 2, 4, 6 and 20 h under a gas mixture of 60% N-2-40% H-2. The magnetic state of the gamma(N) 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 gamma(N)-(Co,Cr,Mo) phase is provided by the observation of stripe domain structures and the hysteresis loops. The ferromagnetic state for the gamma(N) phase observed here is mainly linked to large lattice expansions (similar to 10%) due to high N contents (similar to 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, gamma(N)-(Fe,Cr,Ni) and gamma(N)-(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 gamma(N)-(Co,Cr,Mo) and gamma(N)-(Fe,Cr,Ni) phases may be correlated with the volume dependence of the magnetic properties of fcc-Co/Co4N and fcc-Fe/Fe4N, respectively. (C) 2011 Elsevier B.V. All rights reserved.

【 授权许可】

Free