Combined thermal desorption spectroscopy, hydrogen visualization, HRTEM and EBSD investigation of a Ni–Fe–Cr alloy: The role of hydrogen trapping behavior in hydrogen-assisted fracture

The role of hydrogen trapping behavior in hydrogen-assisted cracking in a Ni–Fe–Cr alloy has been investigated using thermal desorption spectroscopy (TDS), hydrogen visualization, and high-resolution microstructural characterization methods. The results indicate that hydrogen resides at interstitial lattice sites, dislocations, and vacancies with the ascending order of the desorption activation energies. This study firstly shows that hydrogen is trapped reversibly at dislocations including misfit dislocations at the austenite/δ phase interface, and deformation-induced dislocations. The hydrogen trapping behavior is proved by TDS and hydrogen visualization technique. The weakly trapped hydrogen at dislocations provides sufficient hydrogen to build up a required critical hydrogen concentration at potential flaws for crack nucleation and to activate hydrogen enhanced decohesion mechanism. Further, it was found that δ phase precipitation exacerbates the hydrogen embrittlement sensitivity. For the first time, evidence for hydrogen transport by dislocations in a Ni-based alloy is observed by the hydrogen visualization technique.