A team of researchers from Imperial College London, including S. Quan, A. Zafra, E. Martínez-Pañeda, C. Wu, Z. D. Harris, and L. Cupertino-Malheiros, has recently published a study in the journal Nature Communications, shedding new light on how hydrogen affects the cracking of nickel, a metal widely used in the energy industry.
The researchers investigated how different types of grain boundaries in pure nickel respond to varying concentrations of hydrogen. Grain boundaries are the interfaces between tiny crystalline regions, or grains, that make up the metal. The team focused on a property called the coincident site lattice value (Σ-n), which describes the degree of misorientation between adjacent grains. They subjected nickel samples to hydrogen concentrations ranging from 4 to 14 parts per million by weight (wppm) and examined the resulting cracks.
The study found that higher hydrogen concentrations led to more significant embrittlement of the nickel, as evidenced by a larger loss in fracture strain, a smaller reduction in area, and an increase in the percentage of intergranular fracture. The researchers also discovered that the number of cracks was significantly higher on the surface than in the bulk material for the most severe hydrogen charging conditions (8 wppm and above), while a similar number was observed for lower concentrations. Importantly, the propensity for hydrogen-assisted intergranular cracking at different types of grain boundaries was consistent between the surface and the bulk material, indicating that while cathodic charging can promote surface cracks, it does not significantly impact the grain boundaries’ relative susceptibility.
The researchers also identified that Σ-3 boundaries, a specific type of grain boundary, were the most resistant to cracking. This finding contrasts with previous studies on nickel alloys and can be attributed to the segregation energies and reductions in the cohesive strength with hydrogen, with less favorable trapping at the Σ-3 boundaries. The study did not find any evidence of plasticity-mediated cracking initiation.
For the energy industry, these findings are crucial as they can help in the design and selection of materials for hydrogen-related applications, such as hydrogen storage and transportation. Understanding how hydrogen affects the integrity of nickel and other materials can lead to safer and more efficient energy systems. The researchers’ work provides valuable insights into the mechanisms of hydrogen-assisted cracking, which can guide the development of strategies to mitigate this phenomenon and improve the performance of materials in hydrogen-rich environments.
This article is based on research available at arXiv.