High-strength micro impact welding of NiTi wire to brass sheet

Vaporizing foil actuator welding (VFAW) was used to create high-strength and fatigue-resistant solid-state, impact-driven dissimilar welds between NiTi wire and a brass alloy for the first time. VFAW uses the high pressure resulting from a vaporized aluminum foil to impact weld NiTi to brass. The NiTi/brass welds had solid-state wavy interfaces with temperature excursions that are very local to the impact region, leading to no traditional heat-affected zone. The circular shape of the NiTi wire provided additional impact angle, which minimized the unbonded zone in the weld center compared to traditional planar impact welding of two metal sheets. The adjoining area of the interfaces was strengthened through strain hardening from VFAW. This work hardened region resulted in suppression and widening of the martensitic transformation temperature ranges in these dissimilar impact welds. Lap shear testing of the dissimilar NiTi impact welds exhibited a pseudoelastic plateau and maximum stress similar to the NiTi base metal. The resultant joint efficiencies were near 100% compared to less than the approximately 50% of traditional welding technologies. Cycling tests show that the NiTi/brass impact welds exhibited very similar pseudoelastic responses as the NiTi base metal with less than 0.5% irrecoverable strains. Dissimilar impact welding of NiTi to brass provides stronger joining and more design flexibility compared to mechanical joining, positioning the technology to be a solution to producing high-strength actuators and sensors.