Correlation between processing parameters and mechanical properties as a function of substrate polarisation and depth in a nitrided 316 L stainless steel using nanoindentation and scanning force microscopy

The effects of substrate polarisation in a nitrided 316L stainless steel have been investigated in an attempt to accurately correlate processing parameters with surface mechanical properties. Nanoindentation allows the Vickers hardness to be measured at precise depths, meaning that the variation in properties with nitriding depth can be evaluated and correlated with the process parameters. By combining such measurements with surface imaging techniques (scanning force microscopy and scanning electron microscopy) and electron probe micro-analysis, it is possible to explain both the mechanical property and microstructural variations of such layers, having been produced in a low pressure arc plasma discharge at 680 K with a mixed Ar-N2 gas. In this study the nanoindentation technique is presented as a new and valid method for the characterisation of nitrided layers, shown by hardness measurements on four nitrided layers produced with different substrate polarisation potentials. The net advantages of such an approach over conventional methods (e.g. microhardness testing) and the possibility of analysing microstructural phases previously not well detected by X-ray diffraction, make nanoindentation an attractive tool for a more complete understanding of the nitriding process

Statistical error estimation of the Feynman-α method using the bootstrap method

Applicability of the bootstrap method is investigated to estimate the statistical error of the Feynman-α method, which is one of the subcritical measurement techniques on the basis of reactor noise analysis. In the Feynman-α method, the statistical error can be simply estimated from multiple measurements of reactor noise, however it requires additional measurement time to repeat the multiple times of measurements. Using a resampling technique called “bootstrap method,” standard deviation and confidence interval of measurement results obtained by the Feynman-α method can be estimated as the statistical error, using only a single measurement of reactor noise. In order to validate our proposed technique, we carried out a passive measurement of reactor noise without any external source, i.e. with only inherent neutron source by spontaneous fission and (α,n) reactions in nuclear fuels at the Kyoto University Criticality Assembly. Through the actual measurement, it is confirmed that the bootstrap method is applicable to approximately estimate the statistical error of measurement results obtained by the Feynman-α method.Published online: 23 Dec 2015journal articl

Optimum Construction of the Cylindrical Quadrupole Lens

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A way to decrease the nitriding temperature of aluminium: the low-pressure arc-assisted nitriding process

For the purpose of applications in mechanics, nitriding of aluminium has been performed in a high-current (300 A), lowvoltage (20–45 V) and low-pressure (0.8 Pa) thermionic arc. Although nitriding of ferrous materials is efficient in this arc-assisted nitriding process even for unbiased workpieces, an additional negative substrate bias voltage is necessary to process aluminium. Ion bombardment is necessary not only for ion cleaning in an Ar–H2 gas mixture but also for the nitriding treatment in Ar–N2. Under these conditions, a compact and continuous aluminium nitride layer with hexagonal AlN phase is formed on pure aluminium at 450°C. The kinetics of aluminium nitride formation at low temperature (between 340 and 460°C) is characterized by a two-stage mechanism comprising first the nucleation and growth of nodular AlN grains, followed by the formation of a continuous AlN layer. The growth rate of the aluminium nitride layer seems to be controlled by the rate of the chemical reaction to form AlN, rather than the rate of nitrogen diffusion. Some tribological tests performed on the aluminium nitride layers are also reported in order to evaluate the improvement in friction and wear behaviour

Study of a low pressure arc discharge plasma enhanced nitriding reactor : application to steels, aluminium and titanium surfaces treatments

Les développements technologiques récents dans le domaine des décharges dites intensifiées ont permis de diminuer les pressions utilisées en nitruration assistée par des décharges diodes. L’objet de cette étude est de caractériser un nouveau procédé de nitruration assistée par un arc transféré. Celui-ci est basé sur une décharge d'arc à filament thermoémissif générée dans une chambre d'ionisation placée au dessus du réacteur de nitruration. Des anodes segmentées distribuées dans le réacteur permettent de créer un plasma basse tension (20-40 V) à fort courant (100-300A) dans des mélanges gazeux Ar-N2 et Ar-N2-H2. Un diagnostic du plasma mène par spectroscopie d'émission optique, a permis de déterminer les mécanismes d'excitation. En particulier, des résultats concernant la chimie en phase gazeuse des ions Ar+ et N2+ ont été mis en évidence. Une partie de cette étude est consacrée à l'analyse du plasma d'argon issus de la chambre d'ionisation, une seconde partie est consacrée à l'étude de la décharge d'arc dans différents mélanges gazeux (Ar-H2, Ar-N2, Ar-N2-H2 et Ar-N2-CH4). Ces résultats sont confrontés à ceux de l'analyse métallurgique d'échantillons en fer armco nitrurés au potentiel flottant et une corrélation entre l'intensité lumineuse des espèces excitées et la réactivité du fer a pu être mis en évidence. L’élaboration de couches nitrurées sur des substrats en acier AISI 316L, en aluminium et en titane a été abordée pour évaluer les potentialités du procédé. La nitruration de pièces en 316L pour différents temps de traitements à deux températures (310 et 410°C) et de pièces en titane (480°C-750°C) a permis de déterminer les cinétiques de croissance et les structures des couches de diffusion. La concentration superficielle en azote diminue avec la température même lorsque les caractéristiques du plasma ne sont pas modifiées ; ceci est probablement du à la recombinaison de l'azote à l'interface plasma-solide. L’influence de la polarisation des pièces en 316L et en aluminium a été étudiée afin de corréler les paramètres du procédé aux propriétés de surfaces ; en particulier, un compromis entre un décapage ionique efficace et une polarisation des pièces permet la formation d'une couche continue de nitrure d'aluminium sur l'aluminium

Low temperature nitriding of AISI 316L stainless steel and titanium in a low pressure arc discharge

AISI 316L stainless steel (SS) and titanium nitriding were studied in a low pressure arc-assisted nitriding process where the substrate temperature and the plasma parameters are uncoupled. Lower nitriding temperature limits were explored for constant plasma parameters in Ar–N2 gas mixtures and substrates at floating potential. Nitrogen superficial concentration, layer thicknesses and X-ray diffraction analyses were performed on SS specimens nitrided at two temperatures (580 and 680 K) for different times and titanium nitriding was studied in the temperature range 750–1025 K. At low temperature, the nitriding performances are limited by a plasma–surface phenomenon that probably involves recombination of nitrogen atoms