Complexity, wide size ranges, and often anisotropy are attributes that can describe porous microstructures of thermally sprayed deposits, which present especially difficult challenges for characterization techniques. A number of different methods have been employed over the years found to be both useful and having significant limitations. Currently, a wide range of techniques is available to scientists and engineers, but rarely are their advantages, limitations, and disadvantages fully understood. This review will attempt to present a wide range of characterization tools – from frequently employed optical and scanning-electron imaging techniques, through intrusion porosimetry, to lesser-used X-ray and neutron imaging and scattering techniques.  For each technique its main principle, advantages, and disadvantages will be discussed. It will be shown that, while no technique in itself is sufficient for these challenging materials, in combination it is possible to have a sufficiently complex characterization protocol available. A really powerful and capable characterization protocol may need to combine fast and accessible (“in-house”) tools with sparingly applied advanced scattering and imaging techniques. Such a combination of techniques can then be utilized in studies, where development of a detailed understanding of the processing-microstructure-properties relationships is needed in order to provide sufficient data for development of successful models in the future.
Work supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under contract No. DE-AC02-06CH11357.