Investigation into microstructure and mechanical properties effects on sliding wear and cavitation erosion of Al2O3-TiO2 coatings sprayed by APS, SPS and S-HVOF

In this work, different Al2O3-TiO2 coatings, i.e., Al2O3, Al2O3-13 wt% TiO2 and Al2O3-40 wt% TiO2, produced by various thermal spray processes, namely: (i) atmospheric plasma spraying (APS), (ii) suspension plasma spraying (SPS), and (iii) suspension high-velocity oxy fuel spraying (S-HVOF), were investigated. For spray purposes, micrometer-sized powders and water-based suspensions of fine submicrometer-sized powders were used. The study aimed to investigate the influence of spray technology and spray feedstock characteristics, mainly chemical composition, i.e., TiO2 content, on the properties of the resulting coating. The sprayed coatings were characterised in terms of selected mechanical and wear properties, including fracture toughness, Vickers and instrumental hardness, Young's modulus, sliding wear resistance, and cavitation erosion resistance. The study showed that the sliding wear rate decreased with the increasing hardness, Young's modulus, and the content of the α-Al2O3 phase in the coating. The dominant wear mechanism was fatigue-induced brittle delamination, followed by the adhesive smearing of the wear debris. The dense microstructures characterised by a high hardness and an increased content of α-Al2O3 favored the resistance of coatings to cavitation erosion. Cavitation erosion was initiated at the microstructural discontinuities like pores or microcracks, resulting in damage by brittle failure with cracking and spallation, which ended up forming large cavitation craters.