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Effect of hydrogen on fatigue behavior of a cadmium coated high strength steel

Güleken, Ümran Başak.
C Despite the associated health and safety concerns of Cadmium, this material remains the most commonly used fastener plating material in aerospace applications. The plating operation is done by a well understood and common electrodeposition process. If a cadmium plated part has high strength (1000 MPa and above) then in order to prevent hydrogen embrittlement it must be baked at 191°C for 23 hours, within 2 hours after plating. Yet it has been seen that parts fail due to hydrogen embrittlement during service. The first stage of this study investigated the potential for an 8-hour test (developed by Drehler) instead of the aerospace industry standard 200-hour test (QQ – P – 416). The second phase involved an investigation into the effect of hydrogen on crack initiation-based fatigue life of a modified 4340 steel, utilising a rotating beam fatigue test and presenting data within S – N curves. A batch of as-coated samples and a batch of preloaded samples were fatigue tested by rotating beam testing machine. Although the 8-hour test results indicated possible hydrogen absorption, the fatigue test results showed minimal variation in fatigue performance. The most distinctive detrimental change in fatigue behaviour was observed within preloaded samples. Prediction of the mechanisms leading to premature failure of aerospace components was the ultimate purpose of this work.