Preparation And Properties Of Zirconium Based Powders For High Temperature Thermal Barrier Coatings

High-temperature thermal barrier coatings（TBCs）are a layer of ceramic material attached to the surface of high-temperature metal objects,which can effectively improve the working temperature,thermal efficiency,and service life of thermal power equipment.Zirconium based materials have become an important candidate material for TBCs due to their excellent insulation performance,high-temperature oxidation resistance,high-temperature corrosion resistance,and high strength.However,there are prominent problems in the preparation and application of zirconium based materials,such as the scarcity of rare earth raw materials such as yttrium oxide,the need to improve the usable temperature,the easy growth of powder grains,and the uneven distribution of components.In this paper,the improved assist sol-gel method was mainly used.First,the preparation of CaO-ZrO₂nanocomposite powder was studied in detail,and the preparation rule and reaction mechanism of zirconium based nanocomposite powder were revealed.Then,the preparation rules of CeO₂-ZrO₂,MgO-ZrO₂nanocomposite powders,and calcium zirconate powders under this method were explored.Finally,micro/nano composite powders prepared in different systems were selected to prepare high-temperature thermal barrier ceramics,with a focus on their sintering temperature,bending strength,bulk density,high-temperature oxidation resistance,and corrosion resistance.The results showed that:（1）The CaO-ZrO₂nanocomposite powders prepared with a CaO content of 10 wt%and PEG content of 80 wt%and calcined at 1100℃in vacuum were pure tetragonal zirconia,and had a small particle size and good dispersion,with an average particle size of about 50 nm.Compared to calcination in air,vacuum calcination could not only make the powder particles smaller and more uniform,but also promote the stability of zirconia tetragonal phase.The reason was that the carbon particles formed by pyrolysis of organic matter under vacuum conditions were uniformly distributed on the surface or between the nanoparticles,effectively inhibiting the rapid growth of nanoparticles at high temperatures,facilitating the formation of small particles with high surface energy,thereby promoting the stability of zirconia tetragonal phase under vacuum conditions.And these carbon particles could be effectively removed to ensure the quality of the powders.（2）The CeO₂-ZrO₂nanocomposite powders prepared with CeO₂content of 10 wt%,polyether P123as dispersant and calcined at 1100℃in vacuum were pure tetragonal phase,with uniform particle size distribution and good dispersion.The average size of the powder particles was about 100 nm.（3）The MgO-ZrO₂powders,which contained 5 wt%MgO and were calcined in vacuum,were partially stable tetragonal zirconia with small particle size and narrow particle size distribution.The average particle size of the powders was about 70 nm.（4）The calcium zirconate powders prepared by the assist sol-gel method were calcined at 1300℃in vacuum with the molar ratio of calcium to zirconium of 1:1.The calcium zirconate powders were pure calcium zirconate phase,with small grains and good dispersion.The average size of the powder particles was about 150 nm.（5）Zirconium based high-temperature thermal barrier ceramics were prepared from powders with different phase contents in the above prepared powder systems.Their bending strength,bulk density,high-temperature oxidation resistance,and calcium aluminosilicate（CMAS）corrosion resistance were tested and analyzed.The research showed that high-temperature thermal barrier ceramics such as CaO-ZrO₂,CeO₂-ZrO₂,MgO-ZrO₂,and zirconium based perovskite have high sintering temperatures（1300～1600℃）,excellent flexural strength（175～321 MPa）,and excellent high-temperature oxidation resistance（mass loss is only 1.3%～2.12%after 20 hours at1200℃,and phase change was not significant）.CaO-ZrO₂and MgO-ZrO₂high-temperature thermal barrier ceramics had excellent CMAS corrosion resistance,and there was a clear interface between the corrosion layer and the ceramic layer.Calcium zirconate high-temperature thermal barrier ceramics had good CMAS corrosion resistance,and the interface between the corrosion layer and the ceramic layer was relatively clear,with slight corrosion phenomenon.The CMAS corrosion resistance of CeO₂-ZrO₂high-temperature thermal barrier ceramics was poor,and the corrosion depth reaches half of the ceramic layer.