Topological passivation makes high strength alloys insensitive to hydrogen embrittlement

TL;DR

This paper introduces a topological passivation technique that creates a microstructural layer in alloys, significantly reducing hydrogen embrittlement and enabling high-strength, hydrogen-resistant materials for infrastructure applications.

Contribution

The study presents a novel surface microstructural engineering approach using laminated grains with high dislocation density to prevent hydrogen embrittlement in alloys.

Findings

Decelerates hydrogen migration by up to an order of magnitude

Arrests micro-sized hydrogen-induced cracks at the surface

Almost completely eliminates hydrogen embrittlement at doubled yield strength

Abstract

Infrastructure parts for a hydrogen (H) economy need alloys that are mechanically strong and at the same time resistant to the most dangerous and abrupt type of failure mode, namely, H embrittlement. These two properties are in fundamental conflict, as increasing strength typically amplifies susceptibility to H-related failure. Here, we introduce a new approach to make alloys resistant to H embrittlement, by creating a topological passivation layer (up to a few hundred micrometers thick) near the material surface, the region that is most vulnerable to H ingress and attack. It features instead a layer of ultrafine laminated grains with tens of times higher dislocation density than conventional materials, altering H diffusion, trapping and crack evolution. We tested the concept on a face-centered cubic (FCC) CoCrNi medium entropy model alloy which undergoes severe H-induced intergranular cracking. Two key mechanisms create the topological passivation: First, the high density (up to ~1.3e15 m-2) of H-trapping dislocations within the passivating grain layer decelerates H migration by up to about an order of magnitude, delaying H-induced crack initiation at grain boundaries. More importantly, once unavoidable micro-sized H-induced intergranular cracks emerge in the topmost surface region, they become completely arrested by the laminated grains, due to a transition in the embrittlement mechanism from H-enhanced grain boundary decohesion to highly energy-dissipative dislocation-associated cracking. These effects almost completely eliminate H embrittlement, at even doubled yield strength, when exposing the so architected material to harsh H attack. Our approach leverages surface mechanical treatments to tailor metallic microstructures in surface regions most susceptible to H attack, providing a scalable solution to protect alloys from H-induced damage.