Abstract
Two main challenges in the design of reliable shape memory alloys for medical devices are improving fatigue life and addressing biocompatibility issues such as Ni hypersensitivity. This study presents the optimized design of a low-Ni (Pd, Ni)50(Ti, Al)50 alloy and the characterization of a peak-strengthened Ni-free (Pd, Fe)50(Ti, Al)50 superelastic alloy. Precipitate size, phase fraction, and phase composition are measured using Atom Probe Tomography (APT). From this data, thermodynamic and kinetic descriptions of the 2-phase field containing coherent L21 Heusler precipitates in a B2 matrix are developed. The optimum radius for precipitation strengthening in these systems is determined via experimentally calibrated strengthening models to be 2.3nm. Enhanced fatigue resistance of a peak-strengthened Ni-free alloy design is validated via thermal and mechanical cycling.
| Original language | English (US) |
|---|---|
| Pages (from-to) | S801-S804 |
| Journal | Materials Today: Proceedings |
| Volume | 2 |
| DOIs | |
| State | Published - 2015 |
Funding
This material is based upon work supported by the Nat. Sci. Found. Grad. Res. Fellow. under Grant No. DGE-1324585. The work on low-Ni alloy development was made possible by funding from General Motors R&D center. LEAP measurements were performed at the Northwestern University Center for Atom Probe Tomography (NUCAPT). Funding from NSF-MRI (DMR-0420532) and ONR-DURIP (N00014-0400798, N00014-0610539, N00014-0910781) grants is also acknowledged. NUCAPT received support through the Initiative for Sustainability and Energy at Northwestern and the NSF’s MRSEC program (DMR-0520513 and 1121262).
Keywords
- Fatigue
- Heusler phase
- Medical devices
- PdTi
- Shape memory
- Superelasticity
- Systems design
ASJC Scopus subject areas
- General Materials Science