Masanobu Nunogaki

Surface erosion of graphite by D+ irradiation

Surface erosion of different types of graphite by 20 keV D 2 + ion irradiation has been studied. The surface of isotropic graphite shows deformation in the form of wrinkles, ridges and grooves at a dose of 1.0 × 10 18 D + /cm 2 and smooth features at about 4.0 × 10 19 D + /cm 2 . These changes in surface might be explained by an initial volume change due to stress accumulation and subsequent uniform sputtering erosion. The surface of graphitized paper (PAPYEX) shows a network of uplifting structure after irradiation to a dose of 4.0 × 10 18 D + /cm 2 . Glassy carbon displays minimum surface deformation among the four types of carbon materials studied here. Thermal desorption of D 2 and CD 4 released from graphite irradiated with deuterium ions is independent of the structure of the sample.

NOVEL REACTIVE PLASMA PROCESSING FOR TRANSFORMING SURFACES OF METALS AND INTERMETALLICS TO CERAMICS

The surface of Ti, Zr, and TiAl was directly transformed to ceramics with a graded composition by carburizing, nitriding, and oxidizing using novel reactive plasma processing that has been developed by the present authors. Thick modified layers which consist of TiC, TiN, ZrC, ZrN (Zr2N), ZrO2, and Ti2AlN were successfully synthesized by this plasma process. The ceramic layers exhibited higher hardness and elastic modulus than the substrates. The formation behavior of these ceramic layers was analyzed with ab initio molecular orbital simulation and thermodynamic calculation. The chemical interaction of the interstitial atoms with the lattice of substrate materials was found to govern the diffusion and ordering processes to form the ceramic layers.

Ceramic layers formed on metals by reactive plasma processing

Abstract Thick layers of ceramics mainly composed of TaC, ZrO 2 and Ti 2 AlN were successfully synthesized on the surfaces of Ta, Zr and TiAl by means of novel plasma dry processing with or without 20 MeV-electron beam irradiation as the pretreatment. The thickness of these ceramic layers reached 10–100 μm under appropriate process conditions. Vickers hardness of the layers including TaC, ZrO 2 and Ti 2 AlN were estimated to be approximately 3000, 1300 and 3500 Hv[kg/mm 2 ], respectively. The cross-sectional profiles of constituent elements graded gradually in the modified surface regions, suggesting that these ceramics must have some properties of functionally graded materials.

Direct surface modification of zirconium by reactive plasma processing at elevated temperatures

This paper investigates a surface modification process for Zr to improve its durability, in order to make use of Zr in a blanket module as an effective neutron multiplier with (n, 2n) reaction. Modified ceramic layers were successfully synthesized on Zr substrates by carburizing, nitriding and oxidizing using reactive plasma processes. The microstruc- tural evolution during the plasma process is governed both by the kinetics of the diffusion and by the kinetics of the ordering to form the reaction products. In the case of carburizing, the growth rate of the carbide layer is restrained by the diffusion of C, which was clarified to exhibit high covalency with the neighboring Zr atoms by a first principles molecular orbital simulation, through the layer. By contrast, the diffusion of O which exhibits high ionicity rather than covalency with the Zr lattice is much faster than the rate of ordering to form the monoclinic ZrO2 phase. A 20 MeV electron beam pre-irradiation process was also conducted at ambient temperatures as a pre-treatment before the plasma process. The electron beam irradiation can influence the reaction behavior during the plasma process, depending on the process conditions.

Effects of ion implantation and plasma treatment on tribological properties of aluminium and Al-Mg alloy

Abstract Nitrogen ion implantation and plasma treatment, such as ion nitriding and electron cyclotron resonance (ECR) plasma nitriding, were carried out on pure aluminium and Al-Mg alloys and the tribological properties of the resulting samples were studied. Combined surface treatments, ion nitriding or ECR plasma nitriding, were also conducted after ion implantation. It was found that the Vickers hardness of treated samples increased for both pure aluminium and Al-Mg alloy. The friction coefficient decreased after each treatment in the case of pure aluminium. It was found that nitrogen implantation was effective. The wear volume was also decreased, and the combined treatment of ion implantation and ion nitriding was found to be most effective in decreasing the wear volume of pure aluminium. Scanning electron and transmission electron microscopies of ion nitrided aluminium, treated after implanting, revealed a surface consisting of AlON and AlN+Al layers. For the Al-Mg alloy, ECR plasma nitriding was found to be effective in decreasing the friction coefficient and the wear volume.

Alternation of the Pd Lattice in Nano‐Sized‐Pd/ZrO2 Composite during Hydrogen Absorption

Structural analysis of high Deuterium absorbed 5 nm Pd particles in dispersed ZrO2 has been carried out using XAFS techniques. X‐ray absorption spectra around the Pd K‐absorption edge were observed and analyzed. The Pd–Pd bonding distance in the fcc Pd lattice was enlarged by 0.08 ∼ 0.09 A during absorption of deuterium, and it completely reverted to its original state with the release of deuterium while maintaining the crystal lattice symmetry. These changes provide evidence that deuterium locates not on the surface of the Pd particle, but rather within the Pd crystal lattice. XANES spectra clearly indicate that any change in the oxidation state of Pd are not observed, resulting in no reaction of the absorbed Deuterium atoms with Pd atoms. This paper reports the alternation of Pd lattice in nano‐sized composite during hydrogen absorption. The possible models of deuterium position in the Pd lattice are also discussed.

A several tens-keV monoenergetic positron surface analyzer with 22Na and electrostatic fields

A positron beam surface analyzer equipped with a 10 mCi 22NaCl positron source and three five-element Einzel-lens systems, without guiding magnetic fields, has been constructed. The equipotential surfaces of the electrostatic fields and profiles of the beam trajectories were calculated and tested using an electron gun and the positron source. Meanwhile, a vacuum vessel for UHV was fabricated using large casting blocks of aluminium alloy (#2000) cut by forging and boring without welding. The results ascertained that positrons, moderated with a 10 μm tungsten foil, were accelerated and transported by the electrostatic lens system. Also, the positron beams were extremely sensitive to terrestrial magnetism and to the residual magnetization of materials in and around the electrode system. Concerning the vacuum vessel, the degassing rate of the aluminium chamber, worked on with forging and boring, was ∼ 8.6 × 10−13 Torr l/s·cm2, as low as aluminium from the EX process.

Enhancement of thickness of nitrogen compound layer formed by plasma processing in metals by means of preparative irradiation of electron beam or ion beam

The new surface nitridation processing with use of 20 MeV-electron or 25 keV-Ni + -ion beam irradiation as the preparative processing and the nitrogen plasma treatment as the main processing has been developed for increasing the thickness of nitrogen compound layer and for shortening the nitriding time. As the experimental results, the electron and pre-irradiation were applicable to enhance the diffusion of nitrogen atoms in bulk due to the creation of defects and to promote the adsorption of nitrogen to the sample surface dependently on ion species and fluence, respectively.

Monoenergetic positron beam formation with 22 Na and electrostatic field

A 30 keV-positron beam surface analyser with use of 10 mCi 22 Na has been designed and constructed, although the full-scale test with RI has not been carried out yet. The vacuum chamber was made of large casting block of alluminium alloy for its short half-life of radioactivity by means of forging and boring without welding. Resultantly, the new fablication process of aluminium alloy has been developed for attaining UHV. The degas rate was so low as below 8.6× 10 -13 Torr·L/s·cm 2 .

Protection against arc erosion of 316 stainless steel by plasma source nitridation

The effects of surface nitridation of 316 SS on protection against arc erosion and on suppression of plasma cooling were investigated by using thermal shock loading of 75 J/cm2. The volume loss by arcing was remarkably reduced by nitridation to about 16. Meanwhile, the mass loss increased by nitridation to about 4 times as much as for the non-nitrided sample. It was understood by XMA analysis of the nitrided sample before and after arcing that the increased mass loss was mainly due to nitrogens released from the nitrided sample by arcing. The nitrided to non-nitrided ratio of the total radiated power of impurities released from the samples by arcing was roughly estimated to be about 0.47 despite the increase of the mass loss by nitridation.