The objective of this research is to develop a novel injection technology that will allow quick and inexpensive fabrication of coatings comprised of nanoscale features. Virtually any material that can be dispersed in a solvent and that melts can be manufactured using this process. The approach is to disperse nanosized powders in a solvent to form a colloidal slurry, then spray the slurry into a plasma or a high velocity oxygen fuel (HVOF) generated plume to evaporate the solvent and melt the powder. The forward motion of the powders in the flame causes them to strike the substrate and flatten, forming nanosized "lamellae," which quickly solidify. The processing variables that control lamellae morphology and grain size, include slurry characteristics (powder size and powder loading in the solvent), injection nozzle style, plume type, and substrate temperature and type will be investigated. The resulting microstructure will be studied using X-ray diffraction, transmission electron microscopy, atomic force microscopy, and scanning electron microscopy. Modeling of the impact and solidification behavior of these nanoscale droplets will be performed to compliment the experimental work.
Thermal barrier coatings (TBCs), which protect the metallic structure in a gas turbine engine from temperature extremes, play an important role in the transportation (commercial aircraft) and energy (electricity generation) sectors of the U.S. economy. The use of TBCs allows gas turbines to be operated at higher, more fuel-efficient temperatures. By using the novel injection technology to prepare TBCs with nanocrystalline features it will be demonstrated that thermal conductivity can be significantly reduced as grain sizes approach phonon wavelengths. This will further increase the effectiveness of TBCs to protect the metallic structure of gas turbines. In conjunction with a special undergraduate research program established at the university, this proposal will provide engaging research opportunities for undergraduates.
