Wire-arc directed energy deposition of NiTiCu on NiTi substrate: Microstructure and shape memory behavior

Wire-arc directed energy deposition (DED) is an additive manufacturing technique gaining attention for its ability to produce complex composite structures efficiently and cost-effectively. In this study, a 0.8 mm Ni 45 Ti 50 Cu 5 wire was used to print a wall on a Ni 50.8 Ti 49.2 substrate, forming a NiTi/NiTiCu bi-layer and a 4-layer Ni 45 Ti 50 Cu 5 wall. The research focused on the effects of post heat treatment on the structure, precipitations, phase transformation temperatures, and mechanical properties of the WAAM-deposited NiTiCu wall including the interface. The study found that continuous Ti 2 Ni precipitates reduced mechanical properties, but heat treatments such as homogenization at 1000°C and aging at 450°C improved shape memory and pseudoelastic properties. The homogenization-aging heat treatment resulted in the globularization of the continuous Ti 2 Ni phase and precipitation of coherent (Ni-Cu) 4 Ti 3 in the Ni-rich regions, which showed the best shape memory effect and pseudoelastic properties. The bi-layer specimen showed the best combination of pseudoelastic effect (PE) of up to ∼20 % and shape memory effect (SME) of up to ∼65 %, after homogenization and aging, while the final Ni 45 Ti 50 Cu 5 printed layer demonstrated a strain recovery of about 90 %. • A defect-free Ni 45 Ti 50 Cu 5 wall was printed on a Ni 50 . 8 Ti 49 . 2 substrate by using wire-arc directed energy deposition. • After printing the first layer, a region of the substrate was melted and in the interface region of wall and substrate, bi-layer with austenite and martensite microstructure was formed. • Two-stage heat treatments dispersed integrated Ti 2 Ni precipitates and encouraged (Ni-Cu) 4 Ti 3 precipitations, showed coherent interface with matrix which has led to improved mechanical properties. • The interface region of the Hom-Age condition shows simultaneous PE (20 %) and SME (65 %), and the final printed layer demonstrated a strain recovery of about 90 %.