The thermodynamics of spinel interphase formation at diffusion-bonded Ni/Al2O3 interfaces |
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| Affiliation: | 1. Materials Department, College of Engineering, University of California, Santa Barbara, CA 93106, U.S.A.;2. Max-Planck-Institut für Metallforschung, Institut für Werkstoffwissenschaft, Seestrasse 92, D-7000 Stuttgart 1, Deutschland;1. School of Materials Science and Engineering, Xi’an University of Technology, Shaanxi, Xi’an 710048, PR China;2. Faculty of Engineering and Environment, Northumbria University, Newcastle upon Tyne NE1 8ST, UK;1. Faculty of Materials Science and Engineering, Warsaw University of Technology, 141 Wołoska St., 02-507, Warsaw, Poland;2. Łukasiewicz Research Network - Institute of Microelectronics and Photonics, 133 Wólczyńska St., 01-919, Warsaw, Poland;3. Faculty of Civil Engineering and Geodesy, Military University of Technology, 2 Kaliskiego St., 00-908, Warsaw, Poland;4. National Center for Nuclear Research, Materials Research Lab, Świerk, Otwock 05-400, Poland;1. AMES Sintered Metallic Components, Cami Can Ubach 8, San Vicenç dels Horts, Barcelona, Spain;2. Institute of Chemical Technologies and Analytics, TU Wien, Vienna, Austria;3. Dpt. Materials Sci & Eng, IAAB, Universidad Carlos III de Madrid, Madrid, Spain;1. Faculty of Materials Science and Engineering, Warsaw University of Technology, 141 Wołoska str., 02-507 Warsaw, Poland;2. Łukasiewicz Research Network - Institute of Microelectronics and Photonics, 133 Wólczyńska str., 01-919 Warsaw, Poland |
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| Abstract: | Interface microstructural development during solid state diffusion bonding of Ni to single-crystal α-Al2O3 has been studied by electron microscopy. Nickel aluminate spinel (NiAl2O4) interphase layers ∼ 1 μm thick formed under high vacuum bonding conditions. Very high vacuum (VHV) annealing caused the spinel to disappear, indicating that its stability depends critically upon the oxygen activity. High vacuum diffusion bonding utilizing initially oxygen-free Ni and oxygen-containing Ni established that spinel formation requires a threshold oxygen activity, and furthermore, that the source of the required oxygen can be oxygen initially dissolved in the Ni. Thermodynamic calculations confirm that the threshold oxygen level necessary to stabilize the spinel increases from 0.006 at.% (60 at.ppm) at 1273 K to 0.025 at.% (250 at. ppm) at 1663 K. Further analysis indicates the spinel exhibits a maximum thickness determined by the difference between the initial and threshold oxygen concentrations and the Ni thickness. Considering the solubility limit of oxygen in solid Ni, the spinel thickness is limited to ∼0.005 times the Ni thickness. The reaction is explored further in the context of diffusion path concepts with a calculated NiAlO phase diagram. |
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