Fostering strengths against hydrogen embrittlement: insights from nanotwin-ability and post-treatment effects in additively manufactured CoCrFeMnNi

This study delves into effects of deep cryogenic treatment (DCT) on enhancing the hydrogen embrittlement resistance of CoCrFeMnNi high-entropy alloy fabricated via laser powder-bed-fusion (L-PBF). Comparatively assessing as-print, conventional heat treatment, and DCT, we uncover how nanotwin formation within matrix serves as a critical mechanism to combat adverse effects of hydrogen embrittlement. This work reveals that DCT not only mitigates inherent residual stresses from L-PBF, thereby fostering dislocation redistribution and microstructural stabilization, but also synergizes with high-density dislocation cells. Our findings articulate a nuanced understanding of microstructural evolution in response to post-treatments and consequential enhancement of hydrogen embrittlement resistance. Laser-based additively manufactured CoCrFeMnNi undergoes post heat treatment and deep cryogenic treatment to tailor dislocations and residual stress.The inherent residual stress acts as the driving force for the redistribution of dislocations, leading to the development of a stable microstructure after deep cryogenic treatment.High-density dislocation cells and hydrogen collaborate to lower the local stacking fault energy, triggering gradient nanotwins.Nanotwin-ability effects by deep cryogenic treatment (77 K × 36 h) on the hydrogen embrittlement resistance of CoCrFeMnNi with interior defects are verified. Laser-based additively manufactured CoCrFeMnNi undergoes post heat treatment and deep cryogenic treatment to tailor dislocations and residual stress. The inherent residual stress acts as the driving force for the redistribution of dislocations, leading to the development of a stable microstructure after deep cryogenic treatment. High-density dislocation cells and hydrogen collaborate to lower the local stacking fault energy, triggering gradient nanotwins. Nanotwin-ability effects by deep cryogenic treatment (77 K × 36 h) on the hydrogen embrittlement resistance of CoCrFeMnNi with interior defects are verified.

本研究聚焦于深冷处理（deep cryogenic treatment, DCT）对提升激光粉末床熔融（laser powder-bed-fusion, L-PBF）制备的CoCrFeMnNi高熵合金抗氢脆性能的作用机制。通过对比打印态、常规热处理及深冷处理试样，本研究揭示了基体内部纳米孪晶的形成是抵御氢脆不利影响的关键机制。本研究表明，深冷处理不仅可缓解激光粉末床熔融制备过程中产生的固有残余应力，进而促进位错重分布与微观组织稳定化，还可与高密度位错胞产生协同效应。我们的研究结果细化了对后处理诱导微观组织演化及抗氢脆性能提升机制的认知。针对激光增材制造的CoCrFeMnNi合金，通过后热处理与深冷处理可实现对位错与残余应力的精准调控：固有残余应力作为位错重分布的驱动力，促使深冷处理后形成稳定的微观组织；高密度位错胞与氢元素协同降低局部层错能，进而诱发梯度纳米孪晶的生成。本研究验证了深冷处理（77 K × 36 h）对含内部缺陷的CoCrFeMnNi合金抗氢脆性能的纳米孪晶形成效应。