TY - JOUR
T1 - Kirkendall pore evolution during interdiffusion and homogenization of titanium-coated nickel microwires
AU - Bhattacharjee, Arun J.
AU - Yost, Aaron R.
AU - Erdeniz, Dinc
AU - Dunand, David C.
AU - Paz y Puente, Ashley E.
N1 - Funding Information:
This research was supported by the National Science Foundation under award number DMR-1611308 (Dr. Judith Yang, program manager). The authors thank Mr. Ajith Achuthankutty (University of Cincinnati) for experimental assistance at the Advanced Photon Source, Prof. Ashwin Shahani (University of Michigan, Ann Arbor) for assistance with the MATLAB script for 3D visualization and measurement of pore volume fraction and Dr. Xianghui Xiao (currently staff scientist at Brookhaven National Laboratory) for assistance with operating the 2-BM beamline at the Advanced Photon Source.
Funding Information:
This research was supported by the National Science Foundation under award number DMR-1611308 (Dr. Judith Yang, program manager). The authors thank Mr. Ajith Achuthankutty (University of Cincinnati) for experimental assistance at the Advanced Photon Source, Prof. Ashwin Shahani (University of Michigan, Ann Arbor) for assistance with the MATLAB script for 3D visualization and measurement of pore volume fraction and Dr. Xianghui Xiao (currently staff scientist at Brookhaven National Laboratory) for assistance with operating the 2-BM beamline at the Advanced Photon Source.
Publisher Copyright:
© 2021 Elsevier Ltd
PY - 2021/7
Y1 - 2021/7
N2 - In-situ and ex-situ X-ray 3D-tomography is used to characterize the microstructure of Ni microwires, with wire diameters spanning 25–100 μm, (i) after vapor-phase deposition of Ti onto their surface and (ii) after subsequent homogenization to achieve the near-equiatomic NiTi composition desired for shape-memory or superelastic behavior. After Ti deposition at 925 °C, wires are partially homogenized, exhibiting a pure Ni core surrounded by concentric shells of Ni3Ti, NiTi and NiTi2 intermetallic phases. Because of the imbalanced Ni and Ti diffusive fluxes, Kirkendall porosity is formed near the center of the wire, which often merges into a single pore in cross-sections, due to spatial confinement of the wire geometry. During subsequent homogenization at 925 °C, these Kirkendall pores grow due to further Ni-Ti interdiffusion, and they coalesce into a single, hollow channel near the central axis of the wire, thus forming a NiTi microtube. In some cases, off-center pores form in addition to the central pore, but these off-center pores do not form continuous channels.
AB - In-situ and ex-situ X-ray 3D-tomography is used to characterize the microstructure of Ni microwires, with wire diameters spanning 25–100 μm, (i) after vapor-phase deposition of Ti onto their surface and (ii) after subsequent homogenization to achieve the near-equiatomic NiTi composition desired for shape-memory or superelastic behavior. After Ti deposition at 925 °C, wires are partially homogenized, exhibiting a pure Ni core surrounded by concentric shells of Ni3Ti, NiTi and NiTi2 intermetallic phases. Because of the imbalanced Ni and Ti diffusive fluxes, Kirkendall porosity is formed near the center of the wire, which often merges into a single pore in cross-sections, due to spatial confinement of the wire geometry. During subsequent homogenization at 925 °C, these Kirkendall pores grow due to further Ni-Ti interdiffusion, and they coalesce into a single, hollow channel near the central axis of the wire, thus forming a NiTi microtube. In some cases, off-center pores form in addition to the central pore, but these off-center pores do not form continuous channels.
KW - A. shape memory alloys
KW - B. diffusion
KW - C. coatings
KW - D. point defect
KW - F. x-ray tomography
KW - in situ
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U2 - 10.1016/j.intermet.2021.107199
DO - 10.1016/j.intermet.2021.107199
M3 - Article
AN - SCOPUS:85103696304
SN - 0966-9795
VL - 134
JO - Intermetallics
JF - Intermetallics
M1 - 107199
ER -