Abstract
In this work, microstructural and mechanical response to hydrogen were investigated for CoCrFeMnNi high-entropy alloy (HEA) additively manufactured by selective laser melting (SLM) with and without heat treatment. Microstructural characterization, thermal desorption analyses, and slow-strain-rate tests were conducted to study the hydrogen trapping behavior and the effects of hydrogen on the deformation and fracture mechanism. The results showed that cell walls with high-density dislocations and Mn segregation provided hydrogen trapping and increased the high hydrogen capacity. This caused hydrogen embrittlement, accompanied by hydrogen-assisted intergranular cracking in as-built CoCrFeMnNi HEA. A heat treatment at 900 ℃ reduced dislocation density of the walls and eliminated the Mn segregation. Interestingly, hydrogen-induced ductilization was enabled in the heat-treated-SLM HEA. This is attributed to an appropriate twinability and twinning strain which greatly suppressed intergranular cracking in the surface layer. Therefore, tuning twinability through the control of microstructure is critical for a transition from hydrogen embrittlement to ductilization for SLM-built HEA.
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