Fatigue resistant elastocaloric effect in TiNi via texture-precipitate synergy

Area of Science:

• Materials Science
• Solid-State Physics
• Thermodynamics

Background:

• Shape memory alloys (SMAs) are crucial for solid-state cooling due to their elastocaloric effect.
• Achieving both high elastocaloric performance and exceptional fatigue resistance remains a challenge for next-generation cooling technologies.

Purpose of the Study:

• To develop a textured TiNi SMA with engineered precipitates for enhanced elastocaloric effect and fatigue resistance.
• To investigate the microstructural and crystallographic factors contributing to the alloy's performance and durability.

Main Methods:

• Controlled directional solidification to fabricate textured TiNi alloy with Ti₄Ni₂O precipitates.
• Microstructural analysis using electron microscopy (TEM, HR-TEM).
• In-situ loading X-ray diffraction and digital image correlation for mechanical and transformation analysis.

Main Results:

• Achieved a large adiabatic temperature change (-15.9 K) with excellent fatigue resistance (10 million cycles).
• Observed columnar B2 grains, uniform Ti₄Ni₂O precipitates, and strong crystallographic texture enabling >6% transformation strain.
• Identified B2/Ti₄Ni₂O interfaces as nucleation sites for martensite, promoting directional growth and preserving functional reversibility.

Conclusions:

• The engineered texture-precipitate architecture in TiNi SMAs is key to achieving both high elastocaloric effect and ultrahigh fatigue life.
• This study provides a design strategy for fatigue-resistant SMAs for long-term elastocaloric cooling applications.