Kazuhisa Kawata

The effect of ion-mixed Ti on the BFe interdiffusion during dynamic mixing

Abstract The effects of ion-mixed Ti on the B Fe interdiffusion during a dynamic mixing treatment on mild steel were investigated. The experiment and the resulting improvements in the mechanical surface properties are described in this paper. For the experiment, mild steel specimens were implanted with 40 keV B ions to fluences of 1 × 1018−5 × 1018 ions/cm2. Separate steel specimens were treated by dynamic mixing processes, in which B-ion implantation to fluences of 1 × 1018−5 × 1018 ions/cm2 and Ti evaporation at a fixed deposition rate of 0.05 nm/s were carried out simultaneously. For the B-ion implanted steel, the thickness of the B Fe mixed layer in the substrate was limited to less than 0.6 μm, and an accumulation of implanted B species in the surface region took place when the fluence exceeded 3.5 × 1018 ions/cm2. The B-ion implantation had little effect in improving the wear property of the steel. For the dynamic mixing-treated steel, TiB2 film was synthesized on the surface and B Fe interdiffusion was found to have taken place beneath the TiB2 film during the treatment. The thickness of the B Fe interdiffused layer reached up to 3 μm, about five times the thickness of the B Fe mixed layer resulting from only the B-ion implantation. This dynamic mixing treatment was far more effective in improving the wear property of the steel than the B-ion implantation.

Structure and mechanical property of boundary lubricating film formed in belt-type CVT oil

Cross-sectional transmission electron microscopy (TEM) was used to study the crystal structure of boundary lubricating films formed during the sliding test in belt-type CVT oil using vane-on-disc type tester. The boundary lubricating films formed at various normal loads were from 10 to 80nm thick. It was observed that every film consisted of one inhomogeneous layer containing P, O, S, Ca, Zn and Fe. HRTEM images and electron diffraction indicated that the layer was a mixture of fine (5-10nm) crystalline particles and amorphous matrix at lower normal loads, while at higher normal loads only fine crystalline grains were observed. Nanoindentation technique was also used to evaluate the mechanical properties of the boundary lubricating film formed at the normal load of 300N, The hardness of the film was compared with that of soft metals such as Ag, Zn, Sn and In. It was found that the hardness of that boundary lubricating film was located in between that of Ag and In. It was concluded that there is a strong correlation between the crystalline state of the boundary lubricating film and the friction coefficient.

MODIFICATION OF METAL SURFACES BY ION IMPLANTATION

This study is specifically directed toward ion beam surface modification of metals. Our current results of the improvement in the corrosion resistance of titanium and the wear resistance of steel are reviewed in this paper. Ta/Ni co-implantation to titanium is effective in preventing the general corrosion in a sulfuric acid solution. B-Fe interdiffused layer formed on steel during the dynamic mixing with Ti-deposition and B-ion implantation significantly increases the duration of the low friction coefficient during the reciprocal motion wear test.

Isothermal Oxidation of Intermetallic TiAl Implanted with Tantalum Ion

The influence of tantalum ion implantation on the oxidation behavior of the intermetallic γ −TiAl has been investigated under isothermal conditions. The implanted TiAl were oxidized at 1273K in a slowly flowing air up to 24 hours. The oxidation reaction was followed thermogravimetrically and the oxide scales were analyzed mainly by using scanning electron microscopy with energy dispersive x-ray analysis. It has been found that tantalum ion implantation leads to a reduction in thermal oxidation of TiAl. The oxidation rate was decreased by nearly a factor of three at fluences above 3×1016 ions/cm2. The oxide scale exhibits layered structure, which is constituted of an external rutile layer and an internal layer mixed with rutile and alumina. Tantalum ion implantation enhanced segregation of the alumina enriched layer, which is protective.