During electrolytic boriding the bath is contaminated with impurities (primarily iron, with small amounts of chromium and manganese) due to the solution of the walls of crucibles made from oxidation resistant Cr−Ni alloys. The molten borax contains almost no nickel ions.
The participation of iron in the formation of the boride coating is inhibited by overcharging of iron ions, and in the precathode zone rich in boron there is constant borothermal reduction of iron oxide with formation of iron borides, which gradually accumulate in the viscous cathodic slime.
With poor contact between the part and the current carrier and high current densities between the cathode surface and bipolar boride particles the borate melt breaks down, which leads to defects in the boride coating such as the pock marks resulting from electroerosion.
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E. S. Makritskii took part in this work.
Zaporozhe Branch of the Dnepropetrovsk Metallurgical Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 43–45, February, 1978.
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Zhluktenko, E.I., Rakitskaya, R.G. & Chel'tsov, V.Y. Effect of iron oxides on the process of electrolytic boriding. Met Sci Heat Treat 20, 133–137 (1978). https://doi.org/10.1007/BF00670307
- Iron Oxide