High-strength NiTi-stainless steel joint fabricated via resistance microwelding

Nickel-titanium (NiTi) shape memory alloys are widely used in biomedical devices because of their superelasticity and shape memory effect. Stainless steel (SS), valued for its mechanical strength, corrosion resistance and low cost, has also been extensively used in medical implants for over a century. Integrating these two materials is essential for next-generation biomedical devices such as multifunctional guidewires. However, reliable joining of NiTi and SS remains challenging due to the formation of brittle phases in the weld. Here we demonstrate a resistance microwelding strategy that enables robust NiTi-SS joining through controlled interfacial melting. By carefully regulating the formation of molten phases, a solid-state bonded interface is achieved with an ultrathin reaction layer (~850 nm) dominated by a Laves phase. This nanoscale interfacial layer provides strong metallurgical bonding while avoiding the excessive brittleness commonly associated with bulk intermetallic formation. The resulting joints combine full functional performance at NiTi direction with the structural flexibility at SS direction, while also exhibiting good resistance to hydrogen embrittlement and electrochemical corrosion, together with reduced Ni ion release and cytotoxicity.