Yoshio Okabe

Electrochemical properties of ion-implanted metal electrodes

Abstract The multi-sweep cyclic-voltammograms of Cr-, Cu-, Ni-, N-, Ar- and Zn- implanted iron electrode/acetate buffer solution (pH 5) systems were measured. Information about the electrochemical behavior, such as anodic dissolution and passivation, of the ion-implanted iron electrodes was obtained from the voltammograms. The anodic peak current density of the voltammograms, I p , was plotted againts the number of potential-sweep cycles, n c . The I p − n c curves were classified into four types of electrochemical properties, from “inert” to “active”. It was found that the I p - n c characteristics are useful to evaluate the reactivity or the durability of the ion-implanted surface layer. The concentration profiles of Cr and Cu implanted in iron were measured by secondary ion mass spectroscopy, and the effect of electrochemical dissolution on the composition of the surface layer is discussed.

Electrochemical properties of ion implanted steel

Abstract The corrosion behaviour of chromium and nickel implanted steel was investigated by means of immersion potential measurement, polarization resistance measurement and the cyclic voltammetry in 0.5M acetate buffer solution (pH 5.0 ± 0.1) at room temperature. Ion implantation has been carried out with doses of 1 × 10 15 , 1 × 10 16 and 1 × 10 17 ions cm 2 at an energy of 150 keV. The electrochemical properties of implanted steel approach those of Feue5f818Cr alloy, as the implanted dose increases. The electrochemical properties of chromium implanted steel with a dose of 1 × 10 17 ions cm 2 at 150 keV are almost the same as those of Feue5f818Cr alloy. Ion implantation at an environmental temperature (typically room temperature) is a useful technique for the improvement of corrosion resistance.

Ion implantation through aluminum thin film deposited on iron

Abstract The effect of ion implantation into aluminum-deposited-iron plates has been investigated with reference to the concentration profiles of aluminum and iron, and the corrosion inhibition. Aluminum thin films ten nanometers thick, were prepared on pure iron substrates by ion beam sputter coating. Argon and oxygen molecule implantations were performed with a dose of 1016/cm2 at an energy of 150 keV. Concentration profiles of aluminum and iron were measured by means of secondary ion mass spectrometry. The corrosion behaviour of these specimens was evaluated by means of the multi-sweep cyclic voltammetry in 0.5 mol/dm3 acetate buffer solutions of pH 5.0 and 3.8. The results show that ion implantation through the deposited thin film results in making the interface of the film-substrate dispersed and improves the corrosion resistance.

Electrochemical properties of chromium-implanted FeCr alloys

Abstract Chromium ions (Cr+) were implanted in Feue5f810Cr, Feue5f815Cr, and Feue5f820Cr binary alloys (where the compositions are in approximate weight per cent) at an energy of 150 keV with fluences of 1 × 1016-1 × 1017 ions cm−2. The polarization curves were measured by means of multisweep cyclic voltammetry in 0.5 (mol Na2SO4) dm−3 solution containing 10−2 (mol H2SO4) dm−3. The anodic peak current in the transpassive region of the polarization curves was found to be proportional to the chromium concentration in the binary bulk alloys. For chromium-ion-implanted Feue5f8Cr alloys the anodic peak current on change in the number of potential sweep cycles showed that the chromium concentration depended on the depth from the specimen surface. The concentration-depth profile obtained by this electrochemical method was in good agreement with that obtained by secondary ion mass spectrometry.

Coloring of iron surface controlled by Ti +O + double-ion implantations

Abstract Ti + O + double-ion implantations in pure iron have been performed with 1 × 10 17 Ti +/cm 2 at 150 keV and with 1 × 10 17 and 2×10 17 O +/cm 2 at 50 or 35 keV at room temperature. Oxidation state of pre-implanted titanium was investigated by means of X-ray photoelectron spectroscopy. Colored surfaces were produced by the double-ion implantations combined with an electrochemical oxidation of the specimens. Colors such as deep blue, purple, and brown appeared after the electrochemical oxidation with cyclic voltammetry in a 0.5 mol/dm 3 acetate buffer solution of pH 5. The mechanism of the coloring is discussed from analysis of the oxidation state of pre-implanted titanium and concentration-depth profiles of the titanium before and after the anodic oxidation of specimen electrodes. These results showed that double-ion implantations are a useful technique to achieve the coloring with corrosion inhibition of iron surfaces.

Comparison between properties of steels implanted with unseparated ions and a selected ion

Abstract Wear and corrosion properties of implanted steels with unseparated ions have been examined by comparing them with those of specimens implanted with selected ions. The gate-valve with a simple target chamber was made for performance of ion implantation without mass separation. Ion beams were produced by an rf-type ion-gun for gaseous elements and by the hollow-cathode type ion-gun for metal elements in order to achieve as pure a beam of ions as possible. When nitrogen or chromium is used as a main element, implanted steels have almost the same properties as those implanted with a single element. The results show that ion implantation in steels even without mass separation is beneficial enough to improve the surface properties.

Target temperature dependence on titanium oxide formation by high-dose oxygen ion implantation into titanium sheets☆

Abstract A study has been made of the formation process of TiO and rutile TiO 2 buried in titanium surface layers by O 2 + implantation with high doses. Titanium sheets were implanted with a 150 keV O 2 + beam density of 1–2 μA cm −2 with doses of 2 × 10 17 to 2 × 10 18 O atoms cm −2 at a target temperature ranging from −60 to 300 °C during ion implantation. X-ray diffraction (XRD) patterns of implanted titanium sheets were measured to estimate the formation of titanium oxides. In the case of higher temperature implantation (50 to about 300 °C) XRD patterns showed the formation of rutile TiO 2 structure beyond the dose of 1 × 10 18 O atoms cm −2 . In the case of lower temperature implantation (−60 to about −30 °C), XRD patterns of implanted titanium indicated only TiO formation for doses exceeding 1 × 10 18 O atoms cm −2 . The structure change from TiO to rutile was not observed in the case of implantation at lower temperature even with high doses. This means that rutile was formed not only by the oxygen atom injection but also by the thermal effect during ion implantation.

Surface layer characterization of iron steels buried titanium compounds by ion implantation

Effects of additional O+-implantation in Ti+-implanted iron on corrosion inhibition and hardness have been investigated by using cyclic voltammetry and Vickers hardness tests. Additional O+-implantation in the relative dose region, O/Ti 2, their effective change disappear a little. TEM observations show the structure change from amorphous to polycrystalline between these relative ratios. Combination of Ti+-O+ double-ion implantation with electrochemical oxidation has produced the colored surface being harder than pure iron surface. We conclude that additional O+-implantation in Ti+-implanted iron is useful for multi-functional surface modification such as improvement of corrosion inhibition, hardening, and coloration of iron substrate.