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.
N1 - Funding Information:
This work was funded by the National Science Foundation under award number DMR-16-11308 . This work made use of the EPIC facility (NUANCE Center-Northwestern University), which has received support from the MRSEC program ( NSF DMR-1720139 ) at the Materials Research Center, and the Nanoscale Science and Engineering Center ( EEC-0118025/003 ), both programs of the National Science Foundation; the State of Illinois ; and Northwestern University . This work also made use of the MatCI Facility which receives support from the MRSEC Program ( NSF DMR-1720139 ) of the Materials Research Center at Northwestern University .
Publisher Copyright:
© 2018 Elsevier Ltd
PY - 2019/1
Y1 - 2019/1
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
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U2 - 10.1016/j.intermet.2018.10.020
DO - 10.1016/j.intermet.2018.10.020
M3 - Article
AN - SCOPUS:85056547841
SN - 0966-9795
VL - 104
SP - 124
EP - 132
JO - Intermetallics
JF - Intermetallics
ER -