Effects of TiO₂ Contents on Phase and Mechanical Properties of Plasma Sprayed Al₂O₃-TiO₂ Coatings

Four kinds of Al₂O₃-TiO₂ coatings with different TiO₂ contents were prepared on cast iron substrate by plasma spraying. X-ray diffraction (XRD) technique combined with the Rietveld whole pattern fitting method was used to determine the phase's content in different coatings. The effects of TiO₂ content on mechanical properties of the coatings were investigated by means of the microhardness measurement and tensile testing. The results indicate that there are a large amount of γ-Al₂O₃, α-Al₂O₃ and a small quantity of amorphous phase in Al₂O₃-3wt%TiO₂ coating; the maximum value of the amorphous content appears, and Al₂TiO₅ phase forms in Al₂O₃-13wt%TiO₂ coating. With the further increase of the TiO₂ content, the amount of the amorphous phase decreases, and Al₂TiO₅ phase's content increases in coatings. There are only α-Al₂O₃ and Al₂TiO₅ phases in the Al₂O₃-40wt%TiO₂ coating. The microhardness of the coatings decrease but the adhesion strength enhance with the increase of TiO₂ contents, this can be attributed to the formation of the Al₂TiO₅ phase.