Corrosion of nickel-titanium, C110, and Al6061 in gallium-based liquid metal alloys

Abstract

Nickel-titanium is one of the most common shape memory alloys (SMAs). These alloys provide the highest actuation density of all active materials. SMA-based actuators are thermally induced and thus are limited in their actuation response frequency, specifically with regard to their slow speed of cooling. Polyalphaolefin and water have been investigated as fluids for active cooling mechanisms. However, a liquid metal may act as a more effective coolant due to its high thermal conductivity. To date, there has been no research on the liquid metal corrosion effects on nickel-titanium, which is crucial to understanding the viability of using liquid metal as an active coolant for SMA-based actuators. In this work, specimens of nickel-titanium alloys were placed in liquid metal-filled crucibles at 220 ◦C for 300 h. The responses of these specimens were compared to that of others composed of elemental Ni and Ti, as well as the common aerospace aluminum alloy Al6061. For the purposes of understanding liquid metal electronics challenges, copper alloy C110 was also investigated. Liquid metals investigated included gallium and gallium-indium-tin eutectic. Specimens were characterized using scanning electron microscopy and energy-dispersive spectroscopy to investigate the surface effects, penetration of liquid metal, and reaction layer chemistry associated with prolonged exposure to the liquid metals.