Takeo Oki

The morphology and orientation of CrN films deposited by reactive ion plating

Abstract CrN films were prepared by reactive ion plating. The influence of preparation conditions (nitrogen pressure, substrate bias voltage and ion current density) on the crystal orientation, morphology and microhardness of the CrN films were investigated. The crystal structure and morphology of these films were characterized by X-ray diffraction and scanning electron microscopy. The compositions of the CrN films were also examined. With increasing bias voltage and ion current density, the morphology of the CrN films changed from a granular structure to a columnar structure. The orientation of the Cr 2 N films changed from (111) to (300) as the substrate bias voltage increased. No clear columnar structure was observed in Cr 2 N films. Cr + Cr 2 N films exhibited very fine granular structures. The highest average value of the microhardness of the CrN films obtained in this work was 2310 kgf mm −2 measured at a 10 gf load.

Formation mechanism of new corrosion resistance magnesium thin films by PVD method

Abstract Magnesium thin films were deposited on cold-rolled steel by physical vapor deposition sputtering technique. The crystal orientation and morphology of the deposited films were investigated by using XRD and scanning electron microscopy, respectively. The effect of crystal orientation and morphology of magnesium films on corrosion behaviors was estimated by measuring anodic polarization curves in deaerated 3% NaCl solution. With the increase of argon gas pressure, the morphology of the deposited magnesium films changed from columnar to granular structure and the diffraction peaks of the film became little sharp and broad. And all the sputtered magnesium films obviously showed good corrosion resistance compared with 99.99% magnesium target metal. Formation mechanism on the crystal orientation and morphology of magnesium films can be explained by applying the effects of adsorption and occlusion of argon gas.

Characteristics of titanium deposits by electrolysis in molten chloride-fluoride mixture

Titanium deposits were prepared on 304 stainless steel substrates by both constant current and pulse current methods in molten KCl-NaCl-LiCl eutectic salts with 2 mol % potassium hexafluorotitanate. The influence of electrolysis conditions on the crystal orientation and morphology of the titanium deposits was investigated by using X-ray diffraction and scanning electron microscopy, respectively. It was found that the orientation index of the titanium deposits varied with temperature, electrolysis time, current density and pulse shape during electrolysis. The deposits showed a granular structure, in which the grains became larger with increase in temperature. Titanium deposits with pulse current above 873 K had a better corrosion resistance than pure titanium sheet.

Electrochemical studies of titanium in fluoride-chloride molten salts

The interaction between titanium and Ti4+ ions (K2TiF6), the electroreduction reaction of Ti4+ ions and the anodic reaction of Ti in KCl−NaCl−KF melts with K2TiF6 at 973 K were studied by means of electrochemical and physical measurements. It was found that the fluoride ions played a very important role in these reactionsIn KCl−NaCl-3 wt % K2TiF6 molten salts with less than 3 wt % KF, the interaction reaction was considered to proceed as Ti4++Ti=2Ti2+. If the bath contained more than 10 wt% KF, the reaction 3Ti4++Ti=4Ti3+ occurred.The electrochemical reduction of Ti4+ (K2TiF6) ions in the molten salts with less fluoride ions was observed to proceed according to three reaction steps, i.e. Ti4++e=Ti3+, Ti3++e=Ti2+, Ti2++2e=Ti. In the case of the fluoride ion concentration being higher, two reduction steps, i.e. Ti4++e=Ti3+, Ti3++3e=Ti were suggested.

Electrodeposition of Zn−Ni−Fe alloy in acidic chloride bath with separated anodes

The electrodeposition of ternary Zn−Ni−Fe alloy films was investigated in acidic chloride electrolyte. Electrodeposition was performed onto mild steel plates at pH 3 and 43°C. The influence of the chloride concentration (ZnCl2, NiCl2 and FeCl2) on the surface appearance and deposit composition, as well as cathodic current efficiency, were investigated. Bright Zn−Ni−Fe alloy deposits were obtained in the electrolyte containing 0.4m of each of ZnCl2 and NiCl2 with 0.02 to 0.08m FeCl2. The influence of current density, pH and temperature were also examined.

Electrochemical studies of zirconium and hafnium in alkali chloride and alkali fluoride-chloride molten salts

The electrochemical reduction of zirconium and hafnium in alkali chloride or fluoride-chloride molten salts on platinum electrodes has been investigated by means of linear and cyclic voltammetry. It has been found that fluoride ions greatly influenced the reduction of zirconium and hafnium in fluoride-chloride melts. It has been proposed that the mechanism for reduction of zirconium and hafnium in baths containing a low concentration of fluoride compounds is different from the mechanism in baths containing a higher fluoride concentration.

Electrochemical studies of titanium ions (Ti4+) in equimolar KClNaCl molten salts with 1 wt% K2TiF6

Abstract The electrochemical reduction of Ti4+ ions in equimolar KClNaCl melts containing less K2TiF6 (1wt%) on a Pt electrode, was studied at 973 K by means of linear sweep voltammetry, stationary current density—potential curve and ac impedance methods. It was found that the reduction of Ti4+ ions in the molten salts proceeded in the following four consequent steps: Ti4+ + e = Ti3+; Ti3+ + e = Ti2+; Ti2+ + 2e = Ti(Pt alloy); Ti2+ + 2e = Ti(pure). And according to ac impedance measurements, the electroreduction reactions were reversible or quasireversible.

Morphology and crystal orientation of chromium thin films deposited by ion plating

Chromium thin films were deposited by ion plating. The influence of argon gas pressure and substrate bias voltage on the morphology and crystal orientation of the films was investigated by using scanning electron micrography (SEM) and x‐ray diffraction. The preferred orientation of the films changed from (110) to (200) with the increase of argon gas pressure. Most of chromium films exhibited columnar structure and the width of the column became smaller at higher argon gas pressure. The chromium film which was deposited at higher argon pressure exhibited a finer granular structure. The microhardness of the films increased with the increase of bias voltage and argon gas pressure.

Metallographic study on alloying of nickel-tin films from stacked single layers through heating

SUMMARY An alloying process for nickel-tin surface films from stacked single layers through heating was investigated from the metallographic viewpoint using X-ray analysis (XRD) and SEM-EDX. Nickel and tin films were produced separately on the steel surface in this order. The thickness of each layer was about 10 μm. The specimens were then heated in an ambient atmosphere or in vacuum using an electronic furnace. The treatment temperatures were 623, 723, 823 and 1123K and the treatment time was 10.8 ks. Once the tin phase on the top of the surface was melted by heating, nickel atoms began to diffuse into the liquid tin phase and various nickel-tin intermetallic compound phases, Ni3Sn4, Ni3Sn2, Ni3Sn were formed. At higher temperatures, tin oxides were formed and, due to the consumption of tin during the oxide formation, the tin content of the intermetallic compounds for tin and nickel was decreased. In vacuum, the oxide did not form.

Electrochemical Evaluation For Sensitization Of Austenitic Stainless Steels Using Neutral Solution

Austenitic stainless steels (JIS SUS 304) were sensitized at 923K for various times and the extent of sensitization was evaluated in 0.6kmol/ mNaCl solution, using two electrochemical methods: cyclic voltammetry and potential step chronoamperometry. Cyclic voltainmograms indicated that sensitized specimens had two types of pitting corrosion, one for chromium depleted zone and the other for grains. The pitting potentials for both types of corrosion measured by cyclic voltammetry had no significant relation to the extent of sensitization. Potential step chronoamperometry was then applied to the evaluation. The potential step chronoamperometry to the pitting potential for grains gave no significant correlation with the sensitization, and the plotted data were scattered randomly. On the other hand, the time integral of current density calculated from potential step chronoamperometry at the pitting potential for chromium depleted zone increased with the extent of sensitization. The latter case can be utilized for the evaluation of sensitization.