Effect of diffusion distance on evolution of Kirkendall pores in titanium-coated nickel wires

Aaron R. Yost, Dinc Erdeniz, Ashley E. Paz y Puente, David C Dunand

Research output: Contribution to journalArticle

Abstract

Microtubes of near-equiatomic nickel-titanium (NiTi) alloys can be created via the Kirkendall effect during Ni–Ti interdiffusion, when nickel wires are surface-coated with titanium via pack cementation and subsequently homogenized. This study explores the effect of diffusion distance upon Kirkendall microtube formation in NiTi by considering a range of Ni wire diameters. For Ni wire diameters of 25, 50 and 100 μm, titanized at 925 °C for 0.5, 2, and 8 h to achieve average NiTi composition, partial interdiffusion occurs concurrently with Ti surface deposition, resulting in concentric shells of NiTi2, NiTi and Ni3Ti around a Ni core, with some Kirkendall porosity created within the wires. Upon subsequent homogenization at 925 °C, near-single-phase NiTi wires are created and the Kirkendall porosity increases, leading to a variety of pore/channel structures: (i) for 25 μm Ni wires where diffusion distances and times are short, a high volume fraction of micropores is created near the final NiTi wire surface, with 1–2 larger pores near its core; (ii) for 50 μm Ni wires, a single, ∼20 μm diameter pore is created near the NiTi wire center, transforming the wires into microtubes, and; (iii) for 100 μm Ni wires, a ∼50 μm diameter irregular pore is formed near the NiTi wire center, along with an eccentric crescent-shaped pore of similar cross-section, resulting from interruption of a single diffusion path, due to the longer diffusion distances and times.

LanguageEnglish (US)
Pages124-132
Number of pages9
JournalIntermetallics
Volume104
DOIs
StatePublished - Jan 1 2019

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Metal coatings
Binary alloys
Powder metallurgy
Titanium
Nickel
Shape memory effect
Titanium alloys
Porosity
Phase transitions
Wire
Microstructure
Cable cores
nitinol
Nickel alloys
Volume fraction

Keywords

  • Diffusion
  • Microstructure
  • Phase transformation
  • Powder metallurgy
  • Shape-memory alloys

ASJC Scopus subject areas

  • Chemistry(all)
  • Mechanics of Materials
  • Mechanical Engineering
  • Metals and Alloys
  • Materials Chemistry

Cite this

Yost, Aaron R. ; Erdeniz, Dinc ; Paz y Puente, Ashley E. ; Dunand, David C. / Effect of diffusion distance on evolution of Kirkendall pores in titanium-coated nickel wires. In: Intermetallics. 2019 ; Vol. 104. pp. 124-132.
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Effect of diffusion distance on evolution of Kirkendall pores in titanium-coated nickel wires. / Yost, Aaron R.; Erdeniz, Dinc; Paz y Puente, Ashley E.; Dunand, David C.

In: Intermetallics, Vol. 104, 01.01.2019, p. 124-132.

Research output: Contribution to journalArticle

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T1 - Effect of diffusion distance on evolution of Kirkendall pores in titanium-coated nickel wires

AU - Yost, Aaron R.

AU - Erdeniz, Dinc

AU - Paz y Puente, Ashley E.

AU - Dunand, David C

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AB - Microtubes of near-equiatomic nickel-titanium (NiTi) alloys can be created via the Kirkendall effect during Ni–Ti interdiffusion, when nickel wires are surface-coated with titanium via pack cementation and subsequently homogenized. This study explores the effect of diffusion distance upon Kirkendall microtube formation in NiTi by considering a range of Ni wire diameters. For Ni wire diameters of 25, 50 and 100 μm, titanized at 925 °C for 0.5, 2, and 8 h to achieve average NiTi composition, partial interdiffusion occurs concurrently with Ti surface deposition, resulting in concentric shells of NiTi2, NiTi and Ni3Ti around a Ni core, with some Kirkendall porosity created within the wires. Upon subsequent homogenization at 925 °C, near-single-phase NiTi wires are created and the Kirkendall porosity increases, leading to a variety of pore/channel structures: (i) for 25 μm Ni wires where diffusion distances and times are short, a high volume fraction of micropores is created near the final NiTi wire surface, with 1–2 larger pores near its core; (ii) for 50 μm Ni wires, a single, ∼20 μm diameter pore is created near the NiTi wire center, transforming the wires into microtubes, and; (iii) for 100 μm Ni wires, a ∼50 μm diameter irregular pore is formed near the NiTi wire center, along with an eccentric crescent-shaped pore of similar cross-section, resulting from interruption of a single diffusion path, due to the longer diffusion distances and times.

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