Slow strain rate tests were performed on quenched and tempered AISI 4340 steel to measure the extent of hydrogen embrittlement caused by electroplating with zincÃ¢Â Â cobalt alloys. The effects of bath composition and pH were studied and compared with results for electrodeposited cadmium and zincÃ¢Â Â 10%nickel. It was found that zincÃ¢Â Â 1%cobalt alloy coatings caused serious hydrogen embrittlement (EI 0.63); almost as severe as that of cadmium (EI 0.78). Baking cadmium plated steel for 24 h at 200 Ã Â°C gave full recovery of mechanical properties but specimens plated with zincÃ¢Â Â 1%cobalt and then baked still failed in 89% of the time of unplated controls. It was shown that hydrogen uptake and embrittlement could be controlled by depositing thin layers of cobalt or nickel at the steel/ coating interface. For example, the least embrittlement was caused by zincÃ¢Â Â 10%nickel (EI 0.037) due to a nickel rich layer with very low hydrogen diffusion coefficient that formed during the initial stages of electroplating. Similarly, a 0.5 m nickel layer was effective in lowering the embrittlement caused by zincÃ¢Â Â 1%cobalt to that of zincÃ¢Â Â 10%nickel. Furthermore, a 0.5 m cobalt layer deposited before a zincÃ¢Â Â 1%cobalt coating gave virtually 100% recovery of mechanical proper
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