Research On The Synthesis And Plasma Spraying Of Thermal Barrier Coating Material Lanthanum Zirconate

This study reported how to fabricate pyrochlore La2Zr2O7(LZO) powder for plasma spraying application through sol-gel self-propagating combustion method, involving main experimental parameters, grain size and purity of the powder. And make the first attempt to get LZO powder through laser+ self-propagating method. Another part is about atmospheric plasma spraying of the mixed feedstock to get qualified thermal barrier coatings with good heat insulation and mechanical properties, the mixed feedstock is a mixture of granulation LZO and purchased YSZ. These works lay foundations for the practical production and application of LZO.The main parameters involved in the sol-gel self-propagating combustion process are temperature of the water bath, the initial PH of the solution, heating temperature and time, etc. The law of the parameters and reaction mechanism was studied by XRD, DSC, TGA_DTA, and SEM. The results of the study show that the sol-gel process is main about complexing reaction of citric acid and metal ion. The LZO precursor can be obtained through the self-propagating of dry sol-gel at 400℃. Through high temperature sintering process at 900℃ nanometer LZO with complete pyrochlore structure is obtained. The increase of the sintering temperature and time are beneficial to grain growth, ZrO2 phase will be found when sintering at 1100℃. The purity of the obtained powder is influenced by sintering temperature, La/Zr, etc. 98% pyrochlore LZO can be collected with appropriate parameter. Optimized preparation process ensured proper feedstock, exhibiting a nanoscale grain size about 54.82 nm, BET specific surface area of 5.6745 m2/g, Linear change of the thermal expansion rate (DL/Lo) with temperature, and high temperature stability.Laser sintering+self-propagating is a new attempt Which merge self-propagating combustion and roasting process into one, and it greatly improve the efficiency of the synthesis of LZO. The synthesis of LZO powder main received the influence of laser power and the number of scanning, which two determined the phase composition of the powder proved by XRD results. The increase of number of laser scanning is conducive to the formation and growth of LZO grain. The laser power is also positive to the growth of LZO grain, but is negative to the formation of other impurity phases and lattice distortion.Different proportions of granulation LZO mixed with purchased YSZ feedstock are used to prepare films through atmospheric plasma spraying and the films show different structures, mechanical and thermal properties. The top ceramic layer is composed of LZO and YSZ phases analysised by XRD. SEM results show small clusters consist of the columnar crystals and equiaxial crystals come from the nucleation, crystallization and grow up of melted nanoparticles and a number of unmelted nanoparticles. What’s more, the average porosity of the coatings increase with the adding of LZO. The reduce of grain size and increase of the content of LZO in the mixture are effective measures to increase the content of LZO phase in the coatings. The areas between different layers are more fragile and fracture first during the tensile test. The adding of LZO is negative to the hardness but positive to the heat insulation performance. The top coatings present evenly distributed small voids when the adding of LZO proportional within 20%. In this work, the heat-insulating capability of the films prepared by 30%LZO feedstock improve obviously. During the thermal shock test, coatings prepared by 30%LZO or 20%LZO feedstock have good thermal shock resistance. The failure principle of thermal shock test is about the extension of small crack step by step because of the variation of stresses.