Laser remelting of plasma sprayed Al 2O 3 ceramic coatings and subsequent wear resistance

Abstract

This paper deals with the laser melting of Al 2O 3 and Al 2O 3+13wt.%TiO 2 ceramic coatings deposited by atmospheric plasma spraying. After laser melting, metastable phase γ-Al 2O 3 transforms into stable phase α-Al 2O 3 in Al 2O 3 coatings, whereas in Al 2O 3+13wt.%TiO 2 coatings besides this phase transformation, TiO 2 may react with Al 2O 3 and transform into TiAl 2O 5. The melting layer becomes much denser and, hence, its hardness has been greatly developed despite the existence of some cracks. Furthermore, the increase in hardness of the melting layers is almost independent of coating type and generally increases with the laser energy density. However, the coating type has a strong influence on the thickness of the laser melting layers. As to the coatings with the same coating type, the depth of laser melting roughly increases with the laser energy density. Finally, it has been found that the introduction of TiO 2 can improve the wear resistance of ceramic coatings, particularly, of the melting layers, although TiO 2 reduces the hardness of these ceramic coatings.