The Study of Nitinol Welds for Electric Generator and Design of SEM Strain Stage for In-Situ Nitinol Stress Testing

Abstract

Laser welded NiTi wires were analyzed using Scanning Electron Microscopy (SEM) for use in an electric generator that is being developed by Kellogg’s Research Labs. The welds between the NiTi shape memory alloy and its mounting rings must be strong enough to withstand loading and thermal cycling. Microstructure in the weld revealed dendrites that look like Ti2Ni, which could be good reason for weld fatigue due to Ti2Ni’s brittle structure. Some cracking was observed, most likely due to the Ti2Ni inelastic composition. Ti2Ni can affect the shape memory properties of these wires. A temperature-controlled strain stage has been designed for in-situ imaging to observe these structures as they are being stressed physically and thermally.