Abstract
The microstructure and corrosion fatigue behavior under artificial seawater environment of 100-mm-thick Ti–6Al–4V alloy joint via vacuum electron beam welding (EBW) was systematically characterized. Obvious microstructural heterogeneity along the transverse direction of as-welded joint was observed. Bimodal-phases microstructure of granular α colonies and β strips compose the microstructure of the base metal (BM). While the microstructure of fusion zone (FZ) comprises single-phase acicular α/α′ martensite. Under corrosive environment of artificial seawater, FZ shows a lower growth rate of corrosion fatigue cracking (CFC) than that in the BM. Increasing content of residual gas contamination worsens the resistance against corrosion fatigue of the FZ of Ti–6Al–4V alloy joint. Results of local electrochemical characterization indicates that the FZ shows a better resistance against electrochemical corrosion than that of the BM. It is deduced that the slower growth rate of CFC observed in the FZ originates from the combined effects of the excellent corrosion resistance of martensite microstructure and the obstructions of interfaces of fine α/α′ laths against growth of CFC. Moreover, the growth mechanisms of CFC in the BM and FZ were discussed involving the microstructural heterogeneity of the EBW joint.
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