High Strength and Fatigue Resistant Welds in NiTi and Brass by Impact Welding

Vaporizing foil actuator welding (VFAW) was used to create high strength and fatigue resistant dissimilar welds between NiTi 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. Advanced techniques were used to characterize the structure, mechanical and functional properties of these impact welds. The results show that NiTi/brass welds had solid-state wavy interfaces with no thermally induced defects. The adjoining area of the interfaces were strengthened compared to the base metals. Martensitic transformation temperature ranges were widened in these dissimilar impact welds. Lap shear tests show that the dissimilar NiTi impact welds exhibited a similar pseudoelastic plateau and maximum stress as the NiTi base metal. The resultant joint efficiencies were near 100 % compared to less than 50 % in 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 crimping, positioning the technology to be a solution to producing high strength actuators and sensors.