This paper presents the results of corrosion investigations performed on thermal spray coatings with different compositions in the Al 2 O 3 -TiO 2 system. The coatings were deposited on stainless steel via APS and HVOF spraying and metallographically prepared cross sections and surfaces were characterized before and after corrosion testing in NaOH and H 2 SO 4 solutions at various temperatures. Opposite of expectations, APS coatings were found to be more corrosion resistant than the denser HVOF-sprayed layers.

Corrosion protection has long been a challenge to thermally sprayed coatings. Alumina is known for its good corrosion properties, although especially thermally sprayed alumina-based coatings corrode if exposed to certain environments. The coating therefore becomes the limiting part for the component lifetime. Besides the corrosion of the coatings themselves, corrosion of the substrate can result from the existing porosity in the coatings. This work shows the influence of corrosion on alumina-based coatings as a function of the TiO 2 content and the coating process used. The effects of corrosion are quantified to enable lifetime prediction and tailoring of protective coatings. The coatings were analyzed using electrochemical methods and were exposed for long periods to acids and bases at 85 °C. Corrosion properties of the coatings were compared with those of bulk parts, prepared by hot-pressing. An electrochemical method was developed to estimate interconnected of porosity as an alternative to long-term corrosion experiments.