Observation of Strain Glass Transition in Additively‐Manufactured TiNiCu Alloys

Strain glass alloys have attracted significant interest owing to their unique properties, such as quasi‐linear superelasticity (SE), a wide operating temperature window, and high fatigue endurance. Laser‐directed energy deposition (L‐DED) has emerged as a versatile technique for processing and tailoring shape memory alloys. However, applying L‐DED to strain glass alloys remains largely unexplored. We report the fabrication of Ti _50−x Ni _35+x Cu ₁₅ ( x ≥ 7) strain glass alloys via L‐DED. Through a Ni‐ and Cu‐rich compositional design combined with the high cooling rates inherent to L‐DED, nanoscale Ti(Ni, Cu) ₂ precipitates (≈30 nm in width) are incorporated into the austenite matrix. Densely dispersed nanoprecipitates suppress martensitic transformation and promote the crossover strain glass transition behavior, evidenced by the absence of macroscopic phase transformation peaks, an abnormal increase in electric resistivity during cooling, frequency‐dependent storage modulus, sequential B2 ↔ B19 ↔B19′ transitions upon cooling, and broken ergodicity. The Ti ₄₃ Ni ₄₂ Cu ₁₅ ( x = 7) alloy demonstrates 1) quasi‐linear SE with minimal hysteresis, 2) adiabatic temperature changes of +4.6 and −3.9°C under a recoverable strain of 1.5%, 3) the quasi‐linear superelastic response is maintained from −30 to +120°C. Our work provided the strategy to introduce strain glass transition into high‐Cu‐content TiNiCu alloys by L‐DED processing.