Hydrogen-Induced Ductility Loss of GH625 Superalloy Under Thermal Hydrogen Charging.

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.