Microstructural characterization of Al_2O_3-13 wt.% TiO_2 ceramic coatings prepared by squash presetting laser cladding on GH4169 superalloy

摘要

In this study, Al_2O_3-13 wt.% TiO_2 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 coatingswere investigated by using scanning electron microscopy, energy dispersive spectroscopy and X-ray diffractometry. Results showthat 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 crosssection 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 bottomregion. Metastable γ-Al_2O_3 phase transforms to α-Al_2O_3 and a new high-temperature phase Al_2TiO_5 forms after laser cladding.