Porous NiTi by creep expansion of argon-filled pores

Scott M. Oppenheimer, David C. Dunand*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

24 Scopus citations

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 languageEnglish (US)
Pages (from-to)70-76
Number of pages7
JournalMaterials Science and Engineering A
Volume523
Issue number1-2
DOIs
StatePublished - Oct 15 2009

Keywords

  • Cellular materials
  • Hot isostatic pressing
  • Metallic foams
  • Microstructure
  • Nitinol
  • Powder metallurgy
  • Stiffness

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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