Influence of the Oxide Film on the Performance and Corrosion Resistance of TiNiCu Shape Memory Alloys as the Heat Engine Actuator

Abstract

Shape memory alloys (SMAs) are utilized as an actuator for the heat engine to harvest energy from low-temperature geothermal sources, such as hot springs, which convert thermal energy into mechanical work. However, the alloy processing and engine design still require optimization to improve performance and durability. To discuss their potential as heat engine actuator, this study investigated the influence of oxide films on the TiNiCu SMAs in terms of surface and structural properties, recovery forces, and corrosion resistance. The results show that the surfaces of the etched samples were relatively coarser than those unetched with lower oxygen content. With the presence of oxide film, the Austenite Finish Temperature (Af) temperature of the unetched SMAs was lower with R-phase transformation. Also, it provided higher recovery force at above Af temperature (as high as 8.3 N at 70-mm displacement). Furthermore, the corrosion resistance of the unetched SMAs was higher than the etched samples, as analyzed by open-circuit potential and linear polarization in natural spring water at 70°C. These findings imply that the presence of oxide film could be beneficial for the SMAs when used as an actuator for heat engines, although it may require further study to investigate its impact on the fatigue behavior of the alloys.