Session: 01-06: Shape Memory Alloy

Paper Number: 111572

111572 - Thermomechanical Processing of NiTiCu Shape Memory Alloy From Button to Wire 

NiTiCu shape memory alloy (SMA) buttons were thermomechanically-processed using conventional methods such as rolling and drawing to produce wire. Substituting Ni for Cu in the NiTi SMA system compositionally creates an SMA with a narrower hysteresis and greater thermomechanical stability in comparison to the commercially available binary NiTi SMA. An SMA with these characteristics processed into a fine diameter wire would ease integration into novel actuation designs aimed to improve control of the thermomechanical response and to reduce energy usage, weight, and mechanical complexity of the system. SMAs are a lightweight and compact alternative option for actuators due to their high energy density capacity allowing the system weight to be reduced by a fraction of conventional actuators. The high work-output associated with SMAs typically exhibits 5-8% actuation strain as a result of a thermally-induced phase transformation while under an applied stress. In this study, we examined a set of (Ni, Cu)-rich and (Ni, Cu)-lean NiTiCu SMA compositions to determine processing parameters for creating wire by using hot and cold working techniques. Hot rolling sections of a 30g button to 1.5 mm diameter wires with an area reduction of ~85 - 90%. The wire diameter was further reduced by cold drawing and intermediate annealing to 1 mm. Electropolishing was performed to remove the remaining oxidation caused by high temperature annealing and to reduce the wire diameter to 0.5 mm. Every processing step was characterized to monitor the evolution of microstructure and thermomechanical properties by using the following techniques: scanning electron microscopy equipped with energy dispersive spectroscopy, differential scanning calorimetry, and synchrotron-radiation x-ray diffraction. The 0.5 mm diameter NiTiCu wires were shape-set using a custom-made device to form small springs. The same shape-setting procedures were used to create NiTi springs from commercially available Flexinol® actuator wire made by Dynalloy. The NiTiCu and NiTi were thermomechanical cycled 50 times to compare the thermoelastic properties and actuation response.

Presenting Author: Faith Gantz University of North Texas

Presenting Author Biography: Faith Gantz is a Ph.D. student of Materials Science and Engineering at the University of North Texas. Ms. Gantz’s research is focused on processing and characterization of shape memory alloys with the goal of improving actuation fatigue life. Ms. Gantz’s previous projects include collaborating with the Dallas Museum of Art Ceramic on their Metal Work Collection and with the Forging Foundation on high-entropy alloy (HEAs) research while working in Dr. Marcus L. Young’s research group. The research produced by laser coating HEAs onto forging die heads earned her the Charles W. Finkl Scholarship sponsored by the Forging Industry Educational and Research Foundation. She was introduced to working with shape memory alloys junior year and has continued working with these unique alloys for her master’s thesis and Ph.D. with the support of the NASA ULI program. As an undergraduate, Ms. Gantz had the opportunity to present her research on the effects of Ni in NiTiHf SMAs during thermo-mechanical processing at SMST 2019 where she won 2nd place in the poster competition. An internship at NASA Glenn Research Center (GRC) came shortly after where she worked primarily on the shape memory alloys database. The internships provided new experiences with failure analysis on fractured thermomechanical samples. After achieving her master’s, Ms. Gantz received another internship at GRC for two terms focused on studying the mechanism behind the hysteresis in shape memory alloys. Her plans include specializing in characterization and thermomechanical processing of shape memory alloys to understand the effects conventional mechanical processing has on precipitation alignment, fatigue life, and overall thermomechanical properties. Through these experiences, Ms. Gantz’s long-term goals are aimed towards improving quality control and failure analysis in the industry or at a national laboratory.