Abstract
Hydrogen embrittlement (HE) causes engineering alloys to fracture unexpectedly, often at considerable economic or environmental cost. Inaccurate predictions of component lifetimes arise from inadequate understanding of how alloy microstructure affects HE. Here we investigate hydrogen-assisted fracture of a Ni-base superalloy and identify coherent twin boundaries (CTBs) as the microstructural features most susceptible to crack initiation. This is a surprising result considering the renowned beneficial effect of CTBs on mechanical strength and corrosion resistance of many engineering alloys. Remarkably, we also find that CTBs are resistant to crack propagation, implying that hydrogen-assisted crack initiation and propagation are governed by distinct physical mechanisms in Ni-base alloys. This finding motivates a re-evaluation of current lifetime models in light of the dual role of CTBs. It also indicates new paths to designing materials with HE-resistant microstructures.
Highlights
Hydrogen embrittlement (HE) causes engineering alloys to fracture unexpectedly, often at considerable economic or environmental cost
By elucidating the surprising dual role of S3 boundaries in HE, our work demonstrates that H-assisted crack initiation and propagation are governed by distinct physical mechanisms in this alloy system
No evidence of intergranular fracture was observed in samples that were not charged with H: failure in them was ductile-transgranular and occurred after onset of necking (Supplementary Fig. 1)
Summary
Hydrogen embrittlement (HE) causes engineering alloys to fracture unexpectedly, often at considerable economic or environmental cost. We investigate hydrogen-assisted fracture of a Ni-base superalloy and identify coherent twin boundaries (CTBs) as the microstructural features most susceptible to crack initiation This is a surprising result considering the renowned beneficial effect of CTBs on mechanical strength and corrosion resistance of many engineering alloys. We find that CTBs are resistant to crack propagation, implying that hydrogen-assisted crack initiation and propagation are governed by distinct physical mechanisms in Ni-base alloys This finding motivates a re-evaluation of current lifetime models in light of the dual role of CTBs. It indicates new paths to designing materials with HE-resistant microstructures. By elucidating the surprising dual role of S3 boundaries in HE, our work demonstrates that H-assisted crack initiation and propagation are governed by distinct physical mechanisms in this alloy system This finding opens new paths to improved failure prediction and to design of HE-resistant materials
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