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.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 124-132 |
| Number of pages | 9 |
| Journal | Intermetallics |
| Volume | 104 |
| DOIs | |
| State | Published - Jan 1 2019 |
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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
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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 journal › Article
TY - JOUR
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
PY - 2019/1/1
Y1 - 2019/1/1
N2 - 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.
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.
KW - Diffusion
KW - Microstructure
KW - Phase transformation
KW - Powder metallurgy
KW - Shape-memory alloys
UR - http://www.scopus.com/inward/record.url?scp=85056547841&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85056547841&partnerID=8YFLogxK
U2 - 10.1016/j.intermet.2018.10.020
DO - 10.1016/j.intermet.2018.10.020
M3 - Article
VL - 104
SP - 124
EP - 132
JO - Intermetallics
JF - Intermetallics
SN - 0966-9795
ER -