The bond strength of sprayed metal coating was determined by means of tensile test.
The specimen consisted essentially of a shaft which were provided with a hole clear through its axis.
A stud was fitted in this hole, with one end to the flat surface of the shaft. The flat surface of shaft and hence the end of stud were pretreated all over. After bonding and spraying, the stud was pulled out of the shaft by means of testing machine. A breaking load P_maz as indicated on the testing machine is concentrated around the end of the stud, from where the bond layer was sheared off. After P_max was measured, smaller loads than P_max were continued to shear off the rest of the bond layers, until the stud was pulled out of the shaft.
The strength of the bond (F_B) layer (h mm thick) is given by
F_B=h⋅f_Bmax=P_max/πd kg/mm
where, d is a diameter of the end of the stud in mm, and f_Bmax is the maximum stress of bond layer. Being represented in F_B or h⋅f_Bmax, the bond strength of coating per unit length can, in any case, be measured by P_max/πd.
The readings for d were 40, 20, 10, 5 and 4mm which meant that the maximum value of the bond strength between the metallic coating of 13 Cr stainless steel (about 1.5mm thick) and the base metal of 0.2 C mild steel prepared by spraying with molybdenum was about 8kg/mm in any case of d. If the bond strength is given by P_max/π/4d²kg/mm², the value will vary with d.

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In general, mechanical polishing of high speed steel involves more difficulties than that of other steels, because of its high hardness. Therefore, it would be very convenient, if electropolishing could serve to substitute the mechanical polishing. However, as tangsten and its double carbide contained in high speed steel have excellent incorrosible property, it is very difficult to obtain smooth surface of this steel from phosphoric acid and sulphuric acid bath conventionally used in electropolishing.
Then, the relation between the qualities of the said steel and electropolishing conditions was studied.
A few considerations on electropolishing conditions of nitric acid and nitric acid-fluoric acid bathes for heat treated high speed steel are as follow;
1) With the quality of the high speed steel nitric acid could be applied to its electropolishing bath as the main constituents.
2) Polishing ability of nitric acid bath is improved by addition of fluoric acid and oxalic acid.
3) Polishing effect depends upon the heat treatment and processing of high speed steel. As in the case of quenching, the more homogeneous is the structure, the easier is the electropolishing.

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The bath composition for chemical finishing consists of metal salts, reducing agents and buffers.
The correlation of these three factors and the optimum concentrations are studied.
The metal salt is selected from the group consisting of nickel sulfate, nickel chloride, nickel ammonium sulfate, nickel nitrate, nickel carbonate and nickel cyanide.
The reducing agent is selected from the group consisting of sodium hydrophosphate, sodium sulfite anhydrate, hy drazin chloride, hydrazin sulfate, hydroquinone and formaldehyd.
The buffer is selected from the group consisting of acetic acid, propionic acid, butylic acid, vallerianic acid, lactic acid, glycolic acid, tartaric acid, citric acid and formic acid.
As for the reducing agents, nothing is superior than sodium hydrophosphate.
The result is as follows:
1. The optimum concentration of nickel sulfate is 50g/l.
2. The optimum concentration of sodium hydrophosphate is 8-15g/l.
3. The optimum concentration of sodium acetic acid is 10g/l.
4. The bath composition for practical operation NiSO₄ 30±20g/l NaH₂PO₂ 10±5g/l CH₃⋅COONa 10±3g/l
5. Thiourea is effective as brightener.

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A new procedure of simultaneous determination of hypophosphite and nickel in electroless nickel plating solution by means of polarography, was proposed.
Excess copper sulfate was added to the mixed solution, and after the solution was Cheated and the copper powder reduced by hypophosphite was filtered, the remaining copper and nickel ion in the filtrate were measured by polarography. The content of hypophosphite was determined from the remaining copper value. It was found that this procedure is convenient to determine hypophosphite and nickel in plating solution.

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Peculiarities of iron plating bath prepared by ferric sulfate, triethanolamine and sodium hydroxide were studied. The main constituent of this bath was found, by absorption spectrum of electrolyte and paper iono-phoresis, to be an organic coordination complex anion charged minus three in which 2mols of triethanolamine were chelatede to Fe⁺⁺⁺. Suitable concentration of the complex anion in the bath should be more than 0.2mol/l, and good adherent bright deposits were obtained at every current dencity between 0.5 and 10A/dm² at room temperature, but cathode current effeciency was lower than 20%.

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