Abstract
The effect of thermal hydrogen charging on the tensile properties of GH625 superalloy was investigated. The results reveal that hydrogen significantly reduces the ductility of the GH625, leading to a shift from microvoid coalescence (MVC)-induced ductile fracture to intergranular (IG) brittle fracture. Random grain boundaries (GBs) are the primary sites for crack initiation. Hydrogen reduces the critical fracture stress of the δ phase at grain boundaries, causing cracking of the δ phase. Under the influence of hydrogen-enhanced localized plasticity (HELP) and hydrogen-enhanced decohesion (HEDE), the δ/γ interface debonds, forming microcracks that propagate along the fractured δ phase, leading to intergranular cracking. Annealing twin boundaries (TBs) serve as secondary sites for crack initiation. Hydrogen-induced local stress concentration promotes twin boundary sliding and hydrogen segregation reduces twin boundary cohesion strength, which is the primary cause of TB crack formation.