Preparation and properties of lanthanum zirconate and thermal barrier coatings

Thermal barrier coating is the most advanced high temperature alloy surface protective coating technology. It is widely used in aviation, aerospace, automobile and large thermal power generation industries. Especially with the gas turbine/aircraft engine towards the direction of high efficient development, on the performance of the ceramic material demand is higher and higher, traditional Y2O3 stable ZrO2 (YSZ) material is hard to meet the demand of high performance, study can replace YSZ used in high temperature thermal barrier coating material become the focus of research both at home and abroad. Lanthanum zirconium (La2Zr2O7, LZ) is considered as a new high temperature thermal barrier coating material with high melting point, stable phase structure and low thermal conductivity. In this paper, La2Zr2O7 base powder was prepared by different methods, and the new zirconium base thermal barrier coating was prepared by using the atmospheric plasma spraying (APS) technique. The thermal expansion coefficient, thermal shock resistance, thermal conductivity and strength of the coating were studied systematically. The main contents and conclusions are as follows:

The powder of La2Zr2O7 was prepared by means of co-precipitation spray granulation technology. Using molten salt method for the first time, the nanometer La2Zr2O7 powder was prepared. The effects of reaction time, reaction temperature and salt material on the phase and particle size of the product were studied. By changing the experimental conditions, the output is properly amplified. After the spray granulation, the fluidity and density of powder can meet the requirements of plasma spraying.

Diction using plasma spraying of two kinds of powder coating was prepared, based on comparing the performance of the two kinds of coating, found that compared with traditional micronstructured thermal barrier coatings, nanostructured ceramic thermal barrier coatings have higher thermal expansion coefficient, higher bonding strength, good thermal shock resistance, low thermal diffusion coefficient and better heat insulation performance.

In this paper, Dy was prepared by using molten salt method. The effects of Dy and Gd ions on the coating properties of La2Zr2O7 were studied. The results show that Dy, Gd doping can obviously improve the bonding strength, thermal shock, thermal expansion coefficient and thermal conductivity of La2Zr2O7 coating.

The effects of Ta ions on the properties of La2Zr2O7 coating were investigated. As the content of Ta increased, the bulk density of the powder was gradually increased. When x is less than or equal to 0.3, the thermal expansion coefficient of La2TaxZr2 – xO7 coating increases as the content of Ta increases, and the bonding strength of the coating increases gradually. As the content of Ta increased, the thermal shock resistance of the coating increased first and then decreased. When x = 0-3, doping Ta can significantly reduce the thermal conductivity of the coating.