Microstructural characterization of Al2O3-13Â wt.% TiO2 ceramic coatings prepared by squash presetting laser cladding on GH4169 superalloy

In this study, Al2O3-13 wt.% TiO2 ceramic powders were precoated on the surface of GH4169 substrate by the squash presetting method. As-preset coatings were clad by a fiber laser. The microstructure, element distribution and phase composition of the clad coatings were investigated by using scanning electron microscopy, energy dispersive spectroscopy and X-ray diffractometry. Results show that the crack formation of the clad ceramic coating can be restrained by substrate preheating and that the pores can be eliminated by reducing the laser beam moving velocity. The clad ceramic coatings characterized by a dense structure, no cracks, low dilution and good metallurgical bonding to substrate were obtained under optimum processing parameters. The cross-section of the clad coating shows three different microstructural regions that consist of fine equiaxed crystals at the upper region, columnar crystals in the middle region and very fine equiaxed crystals at the bottom region. Metastable γ-Al2O3 phase transforms to α-Al2O3 and a new high-temperature phase Al2TiO5 forms after laser cladding.