Laser remelting of plasma sprayed Al2O3 ceramic coatings and subsequent wear resistance

This paper deals with the laser melting of Al2O3 and Al2O3+13wt.%TiO2 ceramic coatings deposited by atmospheric plasma spraying. After laser melting, metastable phase γ-Al2O3 transforms into stable phase α-Al2O3 in Al2O3 coatings, whereas in Al2O3+13wt.%TiO2 coatings besides this phase transformation, TiO2 may react with Al2O3 and transform into TiAl2O5. 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 TiO2 can improve the wear resistance of ceramic coatings, particularly, of the melting layers, although TiO2 reduces the hardness of these ceramic coatings.