Laser processing of yttria stabilised zirconia/alumina coatings on Fecralloy substrates

Laser irradiation was used to produce 5 mol.% yttria stabilised zirconia/alumina (YSZ/Al2O3) composite coatings on Fecralloy substrates. Firstly, electrophoretic deposition was used to produce green ceramic coatings on Fecralloy substrates. Then both thermal sintering and laser melting were used to consolidate and densify the coating. Some coatings after thermal sintering were further treated by using a high power diode laser beam under various operation conditions. Finally, the microstructure and mechanical properties of coatings were examined using electron microscopy and indentation techniques. In addition, the residual stress in the coating was measured using fluorescence spectroscopy. The microstructure of the laser-processed coating has a columnar structure, which relieves some of the stress due to thermal mismatch between the coating and the metal substrate. The hardness of the coating is up to 1600 kg/mm2 with elastic modulus up to 255 GPa. The YSZ contains mainly cubic/tetragonal phases with some metastable tetragonal (t*) phase present. Such coatings have potential in being used as thermal barrier coatings on metal substrates.