Influence of preheating processes on the microstructure of laser glazed YSZ coatings

Laser glazing is considered to be a promising surface sealing technique for thermal barrier coating. The dense top layer with reduced surface roughness and the segment cracks perpendicular to the surface are considered to be suitable for improving the thermal cycling and hot corrosion resistance of these kind of coatings. In present study, yttria stabilized zirconia ceramic coatings were manufactured by atmospheric plasma spraying and then subjected to a Nd-YAG pulsed laser source. During the laser glazing process, coatings were preheated to 600 degrees C and 800 degrees C in order to obtain different microstructure of the laser glazed coatings. The surface morphologies and cross-sections of the coatings were examined by scanning electron microscopy and microhardness measurements of coatings were carried out. The results indicate that preheating process induces a reduction of the grain size of laser glazed coatings in conjunction with an increasing of microhardness and toughness. In addition, preheating also decreases the substrate-coating interface tensile stress which leads to a reduction of crack surface density.