Surface Property Modification of Alumina Sprayed Coatings Using Nd:YAG Laser

Alumina sprayed coating is an important surface processing technology for mechanical and structural components. However, alumina sprayed coating surfaces are normally very rough and have internal pores. In addition, plasma spraying causes a phase transformation from α-Al2O3 to γ-Al2O3 which leads to deterioration of corrosion resistance of the coating. In this study, a pulsed Nd:YAG laser was used to improve the surface properties of alumina sprayed coatings. Phase transformation, surface topography and microstructure of the coatings under various laser irradiation conditions were investigated. A reverse phase transformation from γ-Al2O3 to α-Al2O3 was achieved, and a pore-free surface was generated successfully. Under some laser irradiation conditions, cracks were induced, but they tended to be suppressed by slowing the laser scan speed. Laser-induced material densification was confirmed by cross sectional observation, and the densified region had a columnar microstructure. By increasing energy density or slowing scan speed of the laser, a very thick layer of columnar structure was obtained. The present research demonstrated that the Nd:YAG laser was effective for surface property improvement of alumina sprayed coatings.