Joining of Shape Memory NiTi to Structural Materials Using Ultrasonic Soldering

Shape memory nickel-titanium (NiTi) alloys can recover up to 8% of induced strain allowing such alloys to be used in the creation of solid-state actuators. Despite the unique properties of NiTi alloys, their implementation in structural applications is expensive, complex, and in some cases unfeasible due to limitations of traditional joining techniques. This research investigates the joining of NiTi to itself, aluminum 2024, O1 tool steel, and 304 stainless steel by Ultrasonic Soldering (USS), a process that can solder difficult to wet materials without the use of flux. The USS joints were evaluated through strength testing, optical microscopy, and maximum calculated von Mises equivalent stresses developed during testing. Lap shear tests show NiTi/NiTi, NiTi/aluminum 2024, NiTi/O1 tool steel, and NiTi/304 stainless steel USS joints have average ultimate shear strengths of 30.9 MPa, 53.8 MPa, 37.2 MPa, and 40.6 MPa, respectively.