Simultaneously enhancing strength and hydrogen embrittlement resistance of pure iron via gradient microstructure

Hydrogen embrittlement (HE) of gradient-structured pure iron was studied by slow strain rate tensile tests, microstructural analysis and time-of-flight secondary ion mass spectrometry. As pre-torsion angles increase from 0° to 1400°, yield strength of alloys monotonically increases, but the HE susceptibility first decreases and then increases, with optimal match of improved strength and HE-resistance for pre-torsioned sample at 400°. This correlates with gradient distributions of grain boundary and dislocation hydrogen traps. These results indicate that the construction of suitable gradient structure in alloys is a promising strategy to maximize the strength and HE-resistance synergy.