In situ investigation of hydrogen embrittlement induced by δ phase in selective laser-melted GH4169 superalloy.

• The hydrogen embrittlement in selective laser melted GH4169 alloy was directly studied. • The deep hydrogen trapping ability of the δ phase was extensively obtained. • The deformation behavior of the δ phase was analyzed using atomic-scale characterization. • Hydrogen-promoted dislocation slip localization led to the δ phase fracture. Direct evidence of hydrogen-assisted crack nucleation and propagation associated with the δ phase in the selective laser melted GH4169 superalloy was obtained. The analysis of hydrogen trapping sites using thermal desorption spectroscopy revealed that the δ phase exhibits strong hydrogen capture capability, with a hydrogen desorption activation energy of 35.45 ± 2.51 kJ/mol. In addition, spatially resolved hydrogen mapping conducted by scanning Kelvin probe force microscopy and hydrogen microprint technique provided further evidence for the δ phase as a deep hydrogen trapping site. The atomic-scale characterization sufficiently reveals the deformation mechanism of the δ phase induced by dislocation accumulation. Hydrogen-promoted dislocation slip localization facilitates the formation of microvoid defects in the δ phase, which is the main reason for the δ phase fracture, and induces intergranular and transgranular cracks. (a) Schematic diagram of the in-situ scanning electron microscopy tensile stage. (b) Direct observation captures the hydrogen-assisted crack propagation during in situ tension of a hydrogen-charged specimen. (c) Electron backscattered diffraction inverse pole figure of the hydrogen-assisted crack during the in situ tension captured at a strain of 15.88 %. (d) Hydrogen microprinting results showing the accumulation of Ag nano-particles near the δ phase. (e) Energy level model of hydrogen in the δ phase and the γ-matrix lattice based on the hydrogen thermal desorption spectra results. (f) Transmission electron microscope image of the δ phase ruptured by dislocation slip bands in the hydrogen-charged specimen. (g) Schematic diagram depicting the deformation process of the δ phase based on the atomic-scale characterization results. (h) Schematic diagram revealing the process of hydrogen-assisted crack initiation and propagation. [Display omitted] [ABSTRACT FROM AUTHOR]