Understanding of hydrogen embrittlement (HE), superelasticity (SE), and thermal hysteresis in additively manufactured NiTi shape memory alloys (SMAs) is limited. The functional properties of Wire Laser-Directed Energy Deposition (WL-DED) NiTi are examined: (1) HE, (2) SE, and (3) thermal hysteresis. Samples were hydrogen charged for 6-72 h. The degradation of functional properties was investigated by comprehensive characterization. Results indicated a suppression of reversible strain, a decrease in transformation temperatures (24 h), and hysteresis after 48 h. The intermetallics (Ni 3 Ti/Ti 2 Ni), R-phase suppression, and the B2 austenite to B19’ martensite transformation were discovered. Hydrogen charging (72 h) induces SE partial recovery and hydride formation/hydrogen redistribution. We proposed a dual-stage time-dependent HE model; Stage I (0-48 h): the synergy of HELP + HEDE mechanisms of HE, and Stage II (48–72 h): hydride embrittlement/HE mitigation. The proposed pre-stabilization treatment intentionally shifts hydrogen into deep traps/hydrides, trading a little initial functional performance for improved hydrogen/HE resistance. • Hydrogen charging degrades the superelasticity of AM NiTi shape memory alloy. • Thermal hysteresis narrows non-monotonically due to hydrogen trapping. • Hydrogen peaks at 2840 ppm (48 h), causing max functional properties loss in AM NiTi. • Microstructure shows martensite variation, plate refinement, and microcracks. • Dual-stage hydrogen embrittlement/damage model, pre-stabilization strategy proposed.
Behvar et al. (2026) studied this question.