Abstract
NiTi powders are densified in the presence of argon gas, whose initial pressure is varied between 1 and 33 atm, to create NiTi billets containing isolated Ar-filled pores. Upon vacuum annealing, the pressurized pores expand by creep of the surrounding NiTi matrix at rates which are in agreement with a simple analytical model up to 16% porosity. Beyond this porosity, foaming becomes very slow, as pores connect with each other and with the specimen surface where the gas escapes. This is due to failure of previous NiTi powder boundaries weakened by oxides insoluble in NiTi; this mechanism does not occur in Ti foams which dissolve their oxides at high temperature, allowing higher levels of pore expansion and foam porosity. NiTi with 10-16% porosity exhibits Young's moduli of 48-57 GPa, and may be useful for high-strength, low stiffness biomedical implants with superelastic or shape-memory properties.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 70-76 |
| Number of pages | 7 |
| Journal | Materials Science and Engineering: A |
| Volume | 523 |
| Issue number | 1-2 |
| DOIs | |
| State | Published - Oct 15 2009 |
Funding
This research was supported by U.S. National Science Foundation through Grant DMR-0505772. S.M.O. also acknowledges the U.S. Department of Defense for a NDSEG Fellowship. The authors thank Dr. Jan Frenzel from the Ruhr-Universität Bochum (Germany) for performing chemical analysis of the NiTi samples.
Keywords
- Cellular materials
- Hot isostatic pressing
- Metallic foams
- Microstructure
- Nitinol
- Powder metallurgy
- Stiffness
ASJC Scopus subject areas
- General Materials Science
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering