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
Masoud Moshtaghi, Mahdieh Safyari, Gregor Mori
Abstract
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.