Investigating the effects of thermal barrier and anti-corrosion coatings on Ni–Ti SMAs’ transformation enthalpy and recovery capabilities through ambient actuation

Shape memory alloys (SMAs), such as Ni–Ti, are valuable in structural and aerospace applications for their shape memory and superelastic properties. However, their performance can be degraded by corrosive and high-temperature environments. Although surface coatings such as thermal barrier coatings (TBCs) and anti-corrosion coatings (ACCs) are used for protection, their effects on the phase transformations of SMAs are not well understood. This study evaluates the impact of commercial polymer-based TBC and ACC coatings on the behavior of Ni–Ti SMAs through thermal, mechanical, and microstructural analysis. Results indicate that both coatings maintain the SMA’s phase transformation temperatures. However, the transformation enthalpy decreased for ACC-coated samples and increased for TBC-coated samples compared to uncoated ones. In thermal recovery tests, uncoated samples showed the highest shape recovery, followed by ACC-coated and TBC-coated samples, suggesting a compromise between protection and transformation efficiency. After 100 cycles, ACC coatings deteriorated significantly, while TBC coatings showed only minor cracking. Electrochemical tests confirmed the anti-corrosion effectiveness of the ACC, and thermal analysis verified the insulating property of the TBC. These findings demonstrate the trade-offs between coating functionality and SMA performance, offering practical insights for selecting coatings in SMA systems under thermal cycling conditions.