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 converts thermal energy into mechanical work. However, the alloy processing and engine design still require optimization to improve the performance and durability. This study investigated the influence of oxide films on the TiNiCu SMAs in terms of surface and structural properties, recovery forces, and corrosion resistance, to discuss their potential as heat engine actuator. The results show that the surfaces of the etched samples were relatively coarser than unetched with lower oxygen content. With the presence of oxide film, the Af temperature of the unetched SMAs was lower with R-phase transformation and also provided higher recovery force at above Af temperature (as high as 8.3 N at 70-mm displacement). Furthermore, corrosion resistance of the unetched SMAs were 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 using as an actuator for heat engine, although it may require further study to investigate its impact on fatigue behavior of the alloys.