CASS and corrodkote tests on a decorative plating containing an intermediate cobalt layer from citrates were conducted to examine its high corrosion resistance processes.
Following conclusions were drawn:
(1) Corrosion surroundings had effects on the formation of small blisters.
(2) The electrode potential between each two plating layers had effects on the formation of small blisters under definite surroundings.
(3) The undercoating of cobalt layer should be electrochemically nobler than the bright nickel.
(4) The preferred processes for high corrosion resistance of decorative platings were as follows:
Cu……Co……bright Ni……regular Cr
Cu……semi-bright Ni……Co……bright Ni……regular Cr and their modifications.

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Chromium diffusion coating was applied to the hot blade sections of 12MW gas turbine, in which residual oils called slurry oil and cycle oil of high sulfur contents (2.5-4.5%) from petrochemical plants are fired. The purpose of the coating was to prevent the blades from high temperature corrosion.
The main particulars of the gas turbine for the field test were summarized as follows:
Generated thermal output: 12MW
Fuel: Residual oil
Gas temperature: 732°C (at turbine inlet)
388°C (at turbine outlet)
Exhaust gas flow rate: 95kg/sec
This gas turbine has suffered severe corrosion on the non-treated 1st stage stationary blades made of Inconel 713°C and Udimet 500 alloys after operations of 2, 800 and 4, 400hrs. Moreover, a slighter corrosion was also observed on the non-treated 2nd stage moving blades made of Inconed 700. After investigation, it was confirmed that these corrosions were due to a typical Sulfidation attack at high temperatures.
The 1st stage moving and stationary blades treated with chromium diffusion coating were still kept in the non-attacked state after the operation of 25, 000hrs, wich proved its effectiveness in preventing from such a Sulfidation attack at high temperatures.

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Fatigue tests under rotary bending were performed on specimens of 0.15 and 0.48% carbon steels and high chromium steels coated with aluminum. The effects of surface roughness of specimens before coating, slight notch, and annealing after coating on the fatigue strength were studied.
The results obtained were as follows:
(1) In the steels coated with aluminum by hot dipping, which have alloy layer thicker than about 80μ, the fatigue strength of rough finished (before coating) specimens (H_max was about 30μ) was nearly equal to that of fine finished (before coating) specimens (H_max was less than 1μ).
(2) The fatigue strength of notched specimens generally increased by coating with aluminum by hot dipping. The increasing rate of the fatigue strength due to the coating increased with the decrease in the notch sensitivity index of base alloy: η=(β-1)/(α-1).
The decrease in fatigue strength could be inhibited by annealing in austenitic region for a short time (less than 30min.) and the subsequent furnace cooling.

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The effects of hydrochloric acid on Au films, which had been electrodeposited on Fe substrate from hydrochloric auric chloride baths, were examined by electron diffraction and direct electron microscopic observation.
The following results were obtained:
(1) The coherencies between the Au plate crystals and Fe substrate were the same as the results in the previous paper.
(2) The growth rate of Au films was accelerated by addition of hydrochloric acid to the auric chloride bath.
(3) The addition of hydrochloric acid was effective in cleaning of Fe substrate, owing to its removing action of oxide films, etc. on its surface. Accordingly, the Au films electrodeposited from the bath, containing 20cc HCl/100cc HAu Cl₄, consisted of good single crystals, and the continuity of the film was also improved.

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The incorporation of sulfate radical into the hydrated Cr oxide film formed on the steel surface during the galvanostatic electrolysis for a few seconds in the electrolyte, being composed of 50g/l of chromic acid and a small amount of sulfuric acid, was investigated by the tracer technics using radioactive sulfur (³⁵S).
The results obtained were as follows:
(1) The incorporation of sulfate radical into the hydrated Cr oxide film and its dissolution concurrently occurred during the electrolysis in the same way as the behavior of the hydrated Cr oxide film.
(2) The amount of sulfate radical (m) measured in the hydrated Cr oxide film after t sec. of galvanostatic electrolysis was shown by the following equation:
m=A′/B′(1-e-^B′t)
Where A′: Rate constant of the incorporation of sulfate radical
B′: Rate constant of its dissolution
(3) The amount of sulfate radical in the hydrated Cr oxide film increased with the increases in the applied current density and the concentration of sulfate ion in the electrolyte. The drop of the electrolyte temperature led to increase of sulfate radical incorporated in the hydrated Cr oxide film.
(4) Most (90-95%) of sulfate radical incorporated in the hydrated Cr oxide film was present as water soluble.
(5) Molar ratio (oxide Cr/SO₄^-2) in the hydrated Cr oxide film slightly decreased with the time of electrolysis, and then, became almost constant (3-5) after 10-20sec. of electrolysis.
(6) The conditions of electrolysis for obtaining higher current efficiency in metallic Cr deposition almost corresponded with those for the formation of thicker hydrated Cr oxide film and the incorporation of much greater amount of sulfate radical in the hydrated Cr oxide film.

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