Gas tungsten arc welding of NiTi shape memory alloy and AlCoCrFeNi2.1 eutectic high entropy alloy using a niobium interlayer

Dissimilar fusion welding of a NiTi shape memory alloy and an AlCoCrFeNi 2.1 eutectic high entropy alloy was performed using a niobium interlayer. The unique properties of these materials complement each other, potentially enabling hybrid structures for advanced applications and smart systems. Gas tungsten arc welding with an arc offset technique was employed to create a weld-braze joint at the NiTi-Nb interface while controlling the heat input. Comprehensive microstructural and phase analysis was carried out using optical and electron microscopy, synchrotron X-ray diffraction, and was further supplemented by thermodynamic simulations. Dissolution of the Nb interlayer altered the solidification pathways in the fusion zone, leading to the formation of topologically close-packed phases (including C14 Laves and σ) and Ti 2 Ni. Multiple interfacial reactions at the NiTi interface introduced significant strain, which increased hardness but also acted as stress concentrators during tensile loading. The addition of the niobium interlayer enabled the formation of a stable, crack-free joint, whereas welding without an interlayer resulted in catastrophic cracking.