Unlocking the Thermal Secrets of Shape Memory Alloys with Infrared Imaging
Nickel-titanium (NiTi) shape memory alloys (SMAs) are remarkable materials: when cooled, they can be bent or stretched into new shapes, only to snap back to their original form when heated. This unique property has enabled innovations ranging from surgical implants to anti-scald valves and compact actuators. But to harness their full potential in next-generation technologies, such as solid-state cooling, scientists need to better understand how these alloys behave under stress.
The Challenge of Non-Uniform Thermal Behavior
NiTi SMAs are among the leading candidates for solid-state refrigeration systems due to their exceptional elastocaloric effect (eCE) and superelasticity. However, characterizing their thermal response under mechanical loading is notoriously complex.
“It is well established that the temperature of certain shape memory alloys varies when stress is applied,” explains Dr. Ruien Hu, Scientific Officer at The Hong Kong Polytechnic University (PolyU). “We previously relied on thermocouples, but their single-point measurements could not capture the non-uniform temperature fields across specimens—especially given the inherent heterogeneity of NiTi alloys.”
Turning to High-Speed, Full-Field Infrared Imaging
To overcome this limitation, Dr. Hu’s team adopted a research-grade infrared solution: the FLIR X8583 high-speed thermal camera. The midwave camera offers 1280 × 1024 resolution and advanced optics capable of capturing rapid thermal changes across the entire specimen surface during tensile and compression testing.
“Our setup integrates a tensile testing machine with the FLIR system,” notes Dr. Hu. “While the alloys are stressed, the camera provides real-time thermal mapping, which is vital for studying elastocaloric responses that can’t be resolved by traditional sensors.”
Revealing Hidden Microstructural Influences
Using samples fabricated via Laser Powder Bed Fusion (LPBF), the PolyU researchers uncovered a striking discovery: up to 4.2 K variation in surface temperature within a single specimen.
“Infrared imaging revealed striped thermal patterns during compression-induced elastocaloric effects,” says Dr. Hu. “These inhomogeneities stem from variations in microstructure, grain size, dislocation density, and precipitate distribution, directly influencing functional performance.”
By capturing full-field thermal dynamics, the FLIR X8583 enabled correlations that would have been invisible with point-based measurements.
The FLIR system provided key advantages:
- Precise high-resolution imaging of small samples
- Exceptional frame rates to capture rapid temperature shifts
- Full-field visualization of thermal gradients under stress
With these capabilities, the team was able to:
- Identify the role of microstructural inhomogeneity in SMA performance
- Gain new insights into superelasticity and functional fatigue
- Demonstrate 96.1% recovery after the first test cycle, highlighting excellent durability
“The high resolution and speed of the FLIR camera have transformed our ability to study NiTi alloys,” says Dr. Hu. “It has allowed us to uncover intrinsic thermal behaviors in far greater detail than was previously possible.”
The research is feeding into broader efforts to develop solid-state cooling technologies and adaptive materials. PolyU also credits FLIR’s technical support as instrumental to the project.
“We greatly benefited from the expertise of FLIR’s representative, Mr. Liu Yongbo, who helped us overcome technical challenges. We look forward to continued collaboration and opportunities to share our findings with the wider research community,” adds Dr. Hu.
Detecting the Undetectable
By enabling high-speed, full-field visualization, the FLIR X8583 has become a cornerstone tool in advanced materials research at PolyU. More than just recording temperature, the system reveals the hidden thermal dynamics that dictate material performance- insights essential for accelerating innovation in shape memory alloys and solid-state cooling technologies.
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