Researchers from the Institute of Metal Research of the Chinese Academy of Sciences have established a safety service criterion for critical marine equipment, marking a major advance in the understanding and quantitative assessment of hydrogen-induced damage in titanium alloys under deep-sea conditions.

Their study was published in Acta Materialia December 2.

Titanium alloys are widely used in deep-sea applications due to their excellent mechanical properties and corrosion resistance, which stem from their self-repairing passive oxide films. However, these materials are vulnerable to hydrogen-induced damage, particularly in deep-sea environments where low oxygen concentrations promote cathodic polarization.

Led by Prof. SONG Yingwei, the research team identified a previously unknown phenomenon described as a "hydrostatic pressure-induced positive shift of hydrogen damage threshold potential." Through in-situ hydrogen permeation experiments conducted under simulated deep-sea pressures, they quantified how the threshold potential shifts from -0.41 V (SCE) at atmospheric pressure to -0.21 V (SCE) at 8 MPa, equivalent to a depth of approximately 800 meters.

They further revealed the dual role of hydrostatic pressure in accelerating hydrogen damage. On one hand, it compresses the Helmholtz layer thickness at the electrode surface by about 23%, increasing interfacial electric field strength and exponentially accelerating hydrogen evolution reaction kinetics. On the other hand, it degrades the passive film, reducing its dense inner layer thickness by over 50% (from 3.9 nm to 1.6 nm) while increasing defect density, severely compromising its barrier function against hydrogen penetration.

This work establishes a comprehensive model linking interfacial electric fields, hydrogen evolution kinetics, and passive film properties under high pressure. The findings provide crucial theoretical guidance for designing hydrogen-resistant titanium alloys for deep-sea applications.

By defining a safety service criterion based on the threshold potential for hydrogen damage, the study addresses a key theoretical gap in deep-sea engineering design and offers important support for the long-term safe operation of submersibles, deep-sea stations, and other critical marine equipment.