About this Abstract |
| Meeting |
2026 TMS Annual Meeting & Exhibition
|
| Symposium
|
Fatigue in Materials: Fundamentals, Multiscale Characterizations and Computational Modeling
|
| Presentation Title |
Understanding the Poor Structural Fatigue Life in Precipitate-Free NiTiHf High-Temperature Shape Memory Alloy Under Constant Force Thermal Cycling |
| Author(s) |
Jiaqi Dong, Alexander Demblon, Roberto Orrostieta, Gianna M. Valentino, Ibrahim Karaman, Kelvin Xie |
| On-Site Speaker (Planned) |
Jiaqi Dong |
| Abstract Scope |
This study investigates the constant force thermal cycling fatigue behavior of Ni₅₀.₃Ti₂₉.₇Hf₂₀ high-temperature shape memory alloys, focusing on why precipitate-free alloys exhibit poorer structural fatigue life than their precipitate-bearing counterparts. Three samples were examined: as-extruded (AE, precipitate-free), peak-aged (PA), and overaged (OA). The AE sample showed the lowest structural fatigue life, failing after 580 thermal cycles. Microstructural characterization after 580 cycles revealed the highest crack density in the AE sample, attributed to strain incompatibility from its largest actuation strain and abundant dislocations that likely caused stress concentrations via pile-up at austenite grain boundaries. In contrast, the PA and OA samples exhibited lower actuation strains, reducing strain incompatibility. Their precipitates also likely pinned dislocations. Together, these effects limited crack formation and delayed structural failure. These findings underscore the critical interplay among actuation strain, dislocation activity, and cracking in governing the structural fatigue behavior of shape memory alloys. |
| Proceedings Inclusion? |
Planned: |
| Keywords |
Characterization, Phase Transformations, |