Characterization of powder-precursor HVOF-sprayed Al2O3-ZrO2 coatings

Enhancing mechanical and chemical properties of ceramic coatings is a perpetual objective in the thermal spraying community. Introducing either novel feedstock or thermal spray processes are the most plausible ways to achieve the improvements, such as improved corrosion resistance or damage tolerance. Properties such as quasi-plasticity and ultra-high yield strength of ceramics can be obtained by increasing the number of nanoscale features in the as-sprayed ceramic coating. Currently, thermal spraying using liquid feedstock can produce coatings with very fine microstructures either by utilizing submicron particles in the form of a suspension or through in-situ synthesis. The focus of this work was to obtain bimodal microstructure by using simultaneous powder-precursor HVOF spraying. Nanostructure was achieved from YSZ and ZrO2 solution-precursor and structure with microscale features from conventional Al2O3 spray powder. The microstructure, phase composition and cavitation erosion resistance of the coatings were compared to the conventional HVOF-sprayed Al2O3-coating.