Hydrogen embrittlement in a magnesium grain boundary: a first-principles study

Area of Science:

• Materials Science
• Computational Materials Science
• Solid State Physics

Background:

• Hydrogen embrittlement is a critical failure mechanism in metals, particularly magnesium alloys.
• Understanding hydrogen's interaction with grain boundaries (GBs) is crucial for mitigating its detrimental effects.

Purpose of the Study:

• To investigate the atomistic mechanisms of hydrogen embrittlement in magnesium (Mg) grain boundaries.
• To elucidate the role of hydrogen segregation on the mechanical properties of Mg grain boundaries.

Main Methods:

• First-principles density functional theory (DFT) calculations were employed.
• Fully relaxed tensile and shear test simulations were performed on Σ10(1124)/[1100] tilt Mg grain boundary models.
• Simulations were conducted with and without hydrogen (H) segregation at the GB.

Main Results:

• Hydrogen segregation was found to strengthen the Mg grain boundary due to covalent-like Mg-H bonds, outweighing Mg-Mg bond weakening from charge transfer.
• Macroscopic fracture was suppressed, and elongation to failure was not reduced by H segregation.
• However, resistance to grain boundary shearing increased with H segregation.

Conclusions:

• Hydrogen segregation enhances crack growth at Mg grain boundaries by suppressing dislocation emission from the crack tip.
• This suppression of dislocation emission is identified as the primary mechanism leading to hydrogen embrittlement in magnesium.
• The findings provide critical insights into the complex behavior of hydrogen in magnesium alloys and its impact on mechanical integrity.