Research Of Sm₂Zr₂O₇-NiCr₂O₄Thermal Barrier Coatings With High Emissivity

With the increase of the operating temperatures in the turbine engine, the temperatureof TBCs (thermal barrier coatings) is also rising, which makes the thermal radiation effectsbecause more and more obvious. The rare earth ziconates, which has an excellentapplication prospects in the term of thermal barrier coatings, has a relatively low emissivity,which leads to a little radiation effect. Meanwhile, Because of the infrared transparentcharacterstics of the zirconates at high temperature, the transfer of radiation in the TBCscan not be prevented effectively, that results a reduction of its thermal barrier capabilities.To solve this problem, the conception of radiation heat protection was introducedinto TBCs. Sm2Zr2O7-NiCr2O4composite material with relatively high emissivity wasdesigned and prepared. The tempratuer distribution in the high emissivity TBCs waspredicted by numerical simulation. The TBCs, of which structure was designed andoptimized, was praperd, and its properties were also analyzed.Based on the theoretical of the heat radiation and its interaction with the solid medium,the high meissvity material with spenal structure was introduced to TBCs to enhance itsability of heat dissipation by radition and to ruduce the adverse effect of thermal barrierproperty due to radiation heat transfer. NiCr2O4powder material was synthesis byco-preciptiation method, which was controllable for the phase and grain size. In theco-precipitation process, the PH value was controlled between10and11.5, and theproportion of Ni2+and Cr3+in the mixed solution of metal cations was1.1:2. Thecomposites material of Sm2Zr2O7-NiCr2O4was fabricated by hot-pressing sintering, thereaction at the interface of the two phases was inhibited, and the relative density of thecomposite materials wer above97%. The Infrared emissivity and thermal conductivitsof Sm2Zr2O7-NiCr2O4composite materials were tested by Wears full radiationemission rate calibration verification system and laser pulse method respectively.The results shows that phenomenon of the recovery of thermal conductivities athigh temperature was suppressed or even disappeared by the content of NiCr2O4inthe composits reached to15%, while the infrared emissivity of the composites was0.35. In this condition, the infrared radiation was impeded in the material.The prediction of the temperature distribution in the coating surfaces wasobtained through numerical simulation method. When the temperature of the fluegas reached1900K, the radiation heat flux in the coating became a third of the total heat flux. Through the analysis of the temperature distribution in the coatingsurfaces obtained by the numerical simulation method and the factors whichaffected the heat insulation performance of the coating, three layer structurethermal barrier coatings contained the reflecting layer, the emission layer and theinsulating layer was designed. The surface temperature of the substrate was reduced.The optimized structure of the thermal barrier coating contained the reflector layerwhich was0.05mm thickness of Sm2Zr2O7, the middle layer which was0.05mmthickness of Sm2Zr2O7-15%NiCr2O4composites, and the underlying Sm2Zr2O7layer heat insulation layer of which the thickness was0.15mm. The temperaturereduced158.5K compared with before thermal barrier coating. The singleSm2Zr2O7thermal barrier coating reduced the temperature of substrate by142K.Compared with single Sm2Zr2O7thermal barrier coating, the reduced substratetemperature caused by the three layer thermal barrier coating increased by11.2%.Through the analysis of the various factors affecting the heat insulationperformance of the three-layered thermal barrier coating, the reasons of improvingthe heat insulation performance by the optimization structure was explained and theresearch could provides a theoretical basis and data support for the coatingstructure and component design.The Sm2Zr2O7-NiCr2O4mixture powders were prepared by spray dryinggranulation method. the high emissivity thermal barrier coatings were prepared byatmospheric plasma spraying method. No phase transition and reactions weredetected according to the phase structure of powders and coatings, which meantexcellent chemical compatibility between Sm2Zr2O7and NiCr2O4.Sm2Zr2O7-NiCr2O4composites exhibited good adaptability to spraying process. The insulationresults revealed that the coatings with tripple layers microstructure were superior tothat of the tranditional single layer.The accuracy of the numerical simulation wasverified. At the same time, the tensile strength of the coatings was higher than12MPa, which was similar to the tranditionla coatings.