Research progress in wire arc additive manufacturing of NiTi shape memory alloys

NiTi shape memory alloys （SMAs） have found widespread applications due to their unique superelasticity and shape memory effects. However， traditional manufacturing methods face challenges in fabricating complex geometries and precisely controlling the microstructure NiTi alloys. Wire arc additive manufacturing （WAAM）， with its layer-by-layer deposition characteristics， offers a novel solution for NiTi alloy fabrication. This paper reviews the research progress in WAAM NiTi shape memory alloys， with emphasis on the influence of process parameters on microstructure， phase transformation behavior， and mechanical properties. The advantages and disadvantages of different arc processes （such as gas metal arc welding， gas tungsten arc welding， and cold metal transfer） in NiTi alloy fabrication are analyzed， along with recent achievements in forming quality， phase transformation temperature control， and mechanical properties through WAAM technology. Particular attention is given to the significant microstructural heterogeneity and oxidation issues arising from high heat input， low cooling rates， and repeated thermal cycling during the layer-by-layer deposition process， which adversely affect mechanical properties and superelastic performance. To address these challenges， strategies including process optimization， active cooling， third element addition， and heat treatment are proposed to improve material homogeneity. Furthermore， this paper discusses the heterogeneous structure design of NiTi alloys with other metals， highlighting the potential of WAAM in fabricating multi-material composite structures for high-performance devices. While WAAM demonstrates advantages in fabricating complex geometries and multi-material structures， challenges remain regarding oxidation， element vaporization， and poor interlayer bonding. Future research should focus on heat treatment optimization and microstructural control， development of novel multi-metal composites， and exploration of innovative approaches to enhance interfacial bonding and oxidation resistance， thereby further improving NiTi alloy performance and expanding their application domains.