Evaluating the toughness of APS and HVOF-sprayed Al2O3-ZrO2-coatings by in-situ- and macroscopic bending

Abstract Thermally-sprayed ceramic coatings are commonly used in applications where high wear and corrosion resistance are essential. However, their inherently low toughness and resistance to impacts often limit their use. In bulk ceramics, the toughening effect of ZrO 2 has been successfully implemented in different compositions of Al 2 O 3 -ZrO 2 . Successful toughening leads to increased wear resistance and higher reliability. In this study, APS- and HVOF-sprayed Al 2 O 3 -40ZrO 2 coatings were characterized with SEM and XRD techniques. The toughness of the coatings was evaluated by measuring their strain tolerance with in-situ (SEM) three-point-bending and macroscopic four-point bending with acoustic emission instrumentation. The APS-coatings had a higher strain-to-fracture but failed abruptly. In HVOF-coatings, the cracking commenced earlier but proceeded slower with more crack deflections. The observed behaviour is likely to derive from the coarser microstructure of the APS-coatings, which allows strain distribution in a larger area unlike the finer structure with a lesser melting degree of the HVOF-coatings.