The paper of Prof. Petros Sofronis (Direcor, Principal Investigator, Hydrogen Materials Compatibility Research Division, I²CNER), Prof. Ian Robertson (Principal Investigator, Hydrogen Materials Compatibility Research Division, I²CNER), and their collaborative research group was published in “Acta Materialia“.
A density-functional theory based empirical potential was used to explore the energies of different types of Fe grain boundaries and free surfaces in thermodynamic equilibrium with a hydrogen environment. The classical model for calculating the ideal work of separation with solute atoms is extended to account for every trapping site. This yields the lowest-energy structures at different hydrogen chemical potentials (or gas pressures). At hydrogen gas pressures lower than 1000 atm, the reduction of the reversible work of separation is less than 33% and it increases to 36% at a gas pressure of 5000 atm. Near the hydride formation limit, 5 × 104 atm, the reduction is 44%. Based on the magnitude of these reductions for complete decohesion, and accounting for experimental observations of the microstructure associated with hydrogen-induced intergranular fracture of Fe, it is posited that hydrogen-enhanced plasticity and attendant effects establish the local conditions responsible for the transition in fracture mode from transgranular to intergranular. The conclusion is reached that intergranular failure occurs by a reduction of the cohesive energy but with contributions from structural as well as compositional changes in the grain boundary that are driven by hydrogen-enhanced plasticity processes.
* Title: Effect of hydrogen environment on the separation of Fe grain boundaries
* Authors: Shuai Wang, May L. Martin, Ian M. Robertson, and Petros Sofronis