Evaluation of the densification mechanism during realisation of dense ceramic layers at room temperature via the Aerosol Deposition Method
Synthesis and Properties of Functional Materials
Final Report Abstract
In this project, the deposition mechanism of aerosol deposition was investigated using numerous experimental techniques. For this purpose, various ceramics, glass, and metal powder were successfully deposited on metal, ceramic, glass, and polymer substrates, demonstrating the viability of the AD process for various technologies. Of particular importance was the characterization of the internal residual stress state, which was done with various experimental techniques. Initial studies used BaTiO3 films, where the internal stresses were characterized with FIB-DIC as well as synchrotron x-ray microdiffraction. These measurements showed the large biaxial stress state through the thickness of the film, which had never been shown before. Thermal annealing was also found to reduce the internal stresses considerably, but not eliminate them. In order to determine the local pressures present during deposition, glass was deposited. Raman spectroscopy studies revealed significant densification of the glass structure, indicating local pressures on the order of -10 GPa during deposition. Local crystallization of the glass, which would also give information on local temperature elevations, was not observed, although these studies remain ongoing. A novel technique was developed to directly observe the film/substrate interface after AD deposition. This was accomplished by depositing a film material, in this case NaCl, which was removable with a polar solvent; here we used distilled water. NaCl films were deposited on steel, glass, and ceramic (sapphire) substrates to observe the effect of substrate elastic modulus. Here, it was observed that continuous films were not readily possible on glass or ceramic substrates, whereas films could be deposited on steel substrates. After film removal, XRD on a tilting stage was done in collaboration with Dr. Hall (UK) to determine the residual stresses on the substrate. Interestingly, the AD process resulted in residual stresses of approximately –500 MPa. This is expected to be largely due to the deposition process, where an effect similar to shot peening is present. In conjunction with this work, a DAAD proposal was successfully submitted, facilitating the collaboration with Prof. Ursic and Rojac (Slovenia) on the piezoresponse force microscopy imaging of domains in AD films. Here, this technique was used on an important lead-free ferroelectric material, which undergoes a relaxor-to-ferroelectric transition during mechanical loading. This was used to help determine the internal residual stress distribution in the substrate material through local observations of the resulting domain structure. Finally, various research topics were addressed relating to composite films, such as porous films and multilayered structures. The porous films were realized through the codeposition of NaCl with a ceramic powder, although other film materials, such as glasses and metals, are also feasible. This is a novel technique that has potential wide applications in gas sensors and fuel cells. Development of multilayered AD films is also ongoing, although initial investigations show promising enhancements in the ferroelectric properties and energy storage capabilities.
Publications
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“Contrasting strain mechanisms in lead-free electroceramics” 2nd Seminar on Ferroic Functional Materials & 12th Piezoworkshop, Erlangen (2016)
N.H. Khansur, J.E. Daniels, K.G. Webber
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“Electromechanical response of multilayer ceramic composites made with aerosol deposition” International Union of Theoretical and Applied Mechanics (IUTAM) Symposium on Mechanics of electro/magneto-active materials and structures, Beijing, China (2018)
N.H. Khansur and K.G. Webber
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“Processing of functional ceramic thick films by aerosol deposition” 2018 ISAF-FMA-AMF-AMEC-PFM Joint Conference (IFAAP 2018) Hiroshima, Japan (2018)
N.H. Khansur, K.G. Webber
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“Room temperature deposition of functional ceramic films on low-cost metal substrate”, Ceramics International, 44(14), 16295-16301, (2018)
N. H. Khansur, U. Eckstein, L. Benker, U. Deisinger, B. Merle, K. G. Webber
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“Synchrotron x-ray microdiffraction study of residual stresses in BaTiO3 films deposited at room temperature by aerosol deposition”, Scripta Materialia, 157, 86-89, (2018)
N. H. Khansur, U. Eckstein, K. Riess, A. Martin, J. Drnec, U. Deisinger, K. G. Webber
