On the hydrogen etching mechanism in plasma nitriding of metals (original) (raw)
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New pathways in plasma nitriding of metal alloys
In this paper, we report the effects of oxygen, hydrogen, and deuterium on nitrogen implanted stainless steel AISI 316. The samples were studied in situ by photoemission electron spectroscopy (XPS), nano-indentation (hardness), and scanning electron microscopy (SEM). At relative higher oxygen partial pressures, a surface potential barrier for nitrogen implantation is created by the oxygen absorption. The absorption process obeys a Langmuir isothermal law. The surface barrier is formed by the oxidation of metallic nitrides. The bulk properties such as nitrided layer thickness can be modeled by studying the surface properties. Hydrogen improves the nitrogen content on surface and, consequentially, the hardness in-depth. Surprising efficient oxygen elimination was detected using deuterium instead of hydrogen. This is due to the fact that deuterium improves the nitrogen chemical potential, augmenting the material hardness in depth up to 30% compared to the case when hydrogen is used. This phenomenon is interpreted by an increasing isotope residence time. These novel results suggest that new pathways can be opened in plasma nitriding processes using deuterium in industrial equipment for treatments of metal alloys with stable oxides on the surface.
Oxygen, hydrogen, and deuterium effects on plasma nitriding of metal alloys
We report the oxygen, hydrogen, and deuterium effects on nitrogen implantation of stainless steel. Oxygen is absorbed on the surface creating a potential barrier and diminishing the nitrogen retention. Deuterium removes more oxygen from the surface than hydrogen, augmenting the nitrogen chemical potential and yielding faster nitrogen diffusion into the bulk material.
Effect of hydrogen and oxygen on stainless steel nitriding
The influence of hydrogen and oxygen on stainless steel implanted by nitrogen low-energy ions is systematically studied. It is shown that hydrogen intervenes moderately in the process only when the oxygen partial pressure in the deposition chamber is relatively high. For very low-oxygen partial pressures, the energetic nitrogen molecules impinging on the substrate sputter the thin oxide layer formed on the substrate. This allows the growing of a rich nitrogen layer beneath the surface, improving the diffusing of the implanted atom deeper in the bulk material. For higher-oxygen partial pressures, the sputtering is ineffective, and an oxide layer partially covers the surface even in the presence of hydrogen. The maximum depth penetration of nitrogen depends on the degree of oxygen coverage, which is fairly well described by a Langmuir absorption isothermal. Hardness depth profiling is consistent with the existence of a diffusion barrier formed by the oxygen absorbed on the surface. In order to understand the role of hydrogen on the nitriding process, samples preimplanted with hydrogen were subsequently treated with nitrogen and the hardness depth profiling analyzed. These results may provide a clue about the practical consequences of oxygen and hydrogen on the nitriding process.
Surface & Coatings Technology, 2004
Thermal or radiation enhanced diffusion of nitrogen are extensively utilized for the surface hardening of metallic components. Plasma-immersion ion implantation (PIII) is a newly developed technology, which provides ion implantation at moderate energy (10 -50 keV), and thereby allowing penetration depths deeper than the surface oxide barrier. The damage caused by ion implantation together with the surface sputtering may create favorable boundary conditions for an efficient subsequent diffusive treatment such as nitriding. Surface modification of aluminum alloy 5052, Ti6Al4V alloy and steels (AISI 304 and H13) by a combination of PIII and plasma nitriding (PN) has been investigated. Nitrogen ions were implanted into specimens at 15 kV and then ion nitrided at low pressure with bias of À 800 V. Compared to the untreated samples the hardness of Ti6Al4V alloy and AISI 304 steel could be improved significantly. The hardness of H13 steel can be increased by 20% using a duplex process with 4-h nitriding time. X-ray diffraction (XRD) results have shown some structural modification of the metallic samples and formation of a double-layer structure in AISI 304, treated by PIII and PN. Nitrogen depth profile of the same stainless steel sample, obtained by Auger electron spectroscopy (AES), shows two rather welldefined nitrogen enriched regions with different N contents: high (25 -30 at.%) in a surface layer and medium ( f 10%) in a subsurface layer. D
Analysis of Processes and Properties of Plasma Nitriding
2016
The steady increase worldwide of requirements on the quality and performance of ferrous materials as well as ever stricter environmental regulations make new developments necessary to constantly improve the wear and corrosion protection of components and tools. Furthermore, because the treatment of steel surfaces can cut the need for valuable alloying elements in the base materials, the development of environmentally friendly and industrially applicable methods for the modification and coating of ferrous materials is one of the most important challenges in surface technology. This work is focused on the general characteristics of plasma nitriding, its technical and structural properties, and applications.
In situ photoemission electron spectroscopy of plasma-nitrided metal alloys
2005
In this paper, we report the influence of oxygen on the structure and chemical compositions of the surface of low-energy 50 eV implanted stainless steel studied by in situ photoemission electron spectroscopy. The presence of oxygen at the surface forms thermodynamically stable oxides and hydroxides, degrading metallic nitrides, and preventing efficient nitrogen diffusion into the bulk material. Among these metallic nitrides, N and FeN x are more susceptible to oxidize. Lower oxygen partial pressures augment nitrogen content at the surface determining material bulk properties.
Journal of Magnetism and Magnetic Materials, 2001
The effect of the nitrogen uptake in a-iron upon spark erosion in gaseous and liquid ammonia, plasma nitriding, and plasma immersion ion implantation is studied. The resulting phases and hyperfine parameters, measured by the M. o ossbauer spectroscopy, are discussed from the point of view of initial conditions of their preparation and subsequent heat and/or mechanical treatment. Spark erosion in the ammonia gas produces fine particles with the dominating ferromagnetic a-Fe phase (50%). The 20% of specimen volume form a 0-Fe and a 00-Fe 16 N 2 phases. The last 30% occupy the g 0-Fe 4 N, ferro-and paramagnetic e phases, and g-Fe(N). Nitriding in the liquid ammonia allows to incorporate the higher content of nitrogen into a-iron particles which results in the formation of paramagnetic eðzÞ-Fe 2 N phase. This phase also dominates the surface of a-iron specimen implanted by nitrogen using plasma immersion ion implantation at 3001C/3 h, where high uptake of nitrogen (approx. 30 at%) is reached. Plasma nitriding at 5101C results in the formation of g 0-Fe 4 N phase.