T. Nishiura

Tribological properties of aluminum modified with nitrogen ion implantation and plasma treatment

Abstract Surface modification of Al by a combination of ion implantation and plasma treatment has been investigated from the tribological viewpoint. Nitrogen ions were implanted into pure Al specimens at 90 keV and then ion-nitrided at a few kV for 6 h. The wear test was carried out using a wheel-on-plate-type testing machine. It was shown that these treatments reduce the friction coefficient, the wear rate and increase the hardness. The surface of the Al specimen was observed by optical microscopy and SEM. A lot of blisters emerged on the surface of the treated Al specimen. The TEM observation revealed the detailed surface structure of the modified layer. These results suggest that the combination of the treatments is effective for the modification of tribological properties of the Al surface.

Gamma-ray irradiation effects on interlaminar tearing strength of epoxy-based FRP

Abstract The degradation of interlaminar tearing strength induced by γ-ray irradiation in epoxy-based FRP has been investigated. A remarkable decrease in the tearing strength of FRP was observed for higher doses (above 5 MGy). Observation of the fracture surface revealed that a local fracture propagated along the interface between resin and fiber in the lower dose region, and it took place through the resin in the higher dose region. The fracture through the resin is attributed to the degradation of the resin matrix which is typically revealed as voids in the fracture surface.

Creep behavior of epoxy resin during irradiation at cryogenic temperature

Creep tests of an epoxy resin during bending and irradiation have been carried out to investigate the synergistic effects of radiation and stress on mechanical properties of the resin. Simultaneous application of stress and irradiation on the epoxy resin enhanced creep rates in comparison with the application of stress on an irradiated sample. In order to clarify the mechanism of the radiation-induced creep, measurements of solvent swelling of specimens have been performed. The swelling increased with the dose and the increase of the swelling corresponds to the increase of the chain scission. The mechanism of increased deformation of the resin during irradiation is proposed to be caused by increased chain scission following the release of the local strain energy.

Acoustic emission of composite materials in tensile tests at cryogenic temperatures

Abstract Tensile tests of fibre reinforced plastics are performed at cryogenic temperatures and simultaneously acoustic emission (AE) is observed to examine the microscopic deformation and fracture processes of these materials. AE behaviours at liquid helium temperature are different from those at liquid nitrogen temperature, although the mechanical behaviours are similar. From these results, correlations of the AE sources with the microscopic deformation and fracture processes are discussed.

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.

Creep Test of Composite Materials Under Irradiation Condition

In order to simulate fusion magnet conditions for insulating composite materials, creep tests on the epoxy based FRP were carried out under γ-ray irradiation. The creep deformation under irradiation during the test was much larger than those tested on the non-irradiated and post-irradiated specimens. This result suggests that the radiation damage of FRP in mechanical properties is enhanced by stress and that. therefore, the evaluation of radiation damage using irradiated samples obtained by conventional method can lead to significant underestimation. The mechanism of this enhancement of deformation as well as microscopic deformation mechanisms are discussed on the view point of the change of activation energy in the process of the chemical reaction induced by resin — γ -ray interaction and the separation between matrix resin and reinforcing fibers.

Friction and wear of nitrogen implanted aluminum alloy based FRM

Abstract Aluminum alloy based FRM (Fiber Reinforced Metal) has been implanted with nitrogen ions in order to investigate the effects of implantation on the tribological properties of the FRM. An SiC whisker reinforced aluminum alloy has been chosen as the specimen. The non-mass-analyzed nitrogen ions were implanted up to 10 18 |N/cm 2 at 90 kV using a Z-100 implanter. The friction and wear tests were made using a wheel on plate type testing machine at various friction loads. Appreciable improvements in friction and wear properties are revealed in an oil lubrication condition. The nitrogen implantation suppresses the adhesive wear between the FRM specimen and the stainless steel wheel.

Synergistic effects of radiation and stress on mechanical properties of organic and composite materials

Creep tests of epoxy resin and epoxy-based fibre-reinforced plastics (FRP) in bending during electron-beam irradiation have been carried out. The purpose of this work was to investigate the synergistic effects of radiation and stress on the creep behaviour of FRP at cryogenic temperatures. These materials showed radiation-enhanced deformation when subjected to bending stress applied simultaneously. The creep rate increased with increasing stress and radiation-dose rate. This increase was more severe in epoxy resin than in FRP. The synergistic effects are discussed mainly on the basis of temperature dependence.

Effects of Synergistic Irradiation and Stress on FRP at Cryogenic Temperatures

Creep and relaxation tests of epoxy-based FRP in bending under irradiation condition have been carried out to investigate the synergistic effects of radiation and stress on the mechanical properties of FRP. Simultaneous supply of stress and irradiation on FRP enhanced creep rates and relaxation in comparison with supply of the stress after irradiating. A visco-elastic test and a solvent-swelling test were also carried out to study the molecular changes of the irradiated FRP. Increase of molecular weight between crosslinks was found to be enhanced by the synergistic application of radiation and stress. The mechanism of increased damage of FRP induced by the effects of simultaneous stress and irradiation is discussed.

Frictional behavior in superconducting coil

Experiments were made to obtain information on the role of friction in instability of superconducting coil. We constructed a pin slide type device for friction test which works at cryogenic temperature. The pin slides on the inner most part of the coil wound by Nb-Ti-Zr-Ta conductor. The effect of load and sliding velocity on the friction behavior was examined. The minimum friction energy rate for quenching of the superconducting coils was estimated as a function of friction and magnet operation conditions.