Preparation And Properties Of Lanthanum Zirconate Series Thermal Barrier Coatings

The protection of components in hot end of aero engines and gas turbines has become the core technology of aircraft powerplants,which determines the performance and level of engines to a large extent.Driven by the rapid development of aviation industry in recent years,the upgrading of aero engines is imminent,especially the hot end components that decide the performance of engines.The practical application of the multi-generation engine shows that thermal barrier coating?TBCs?is the most effective way to protect the engine blades from being damaged by high temperature,so we need to develop new thermal barrier coating materials to meet the higher use temperature and the better thermal insulation effect.Lanthanum zirconate in pyrochlore structure?La₂Zr₂O₇,LZ?ceramic material is recognized as one of the candidates for a new generation of thermal barrier.But the LZ thermal barrier coatings has poor thermal shock resistance,studies shows that rare earth doping is an effective measure to improve LZ thermal conductivity and thermal expansion property.In this paper,La and Zr sites co-doped lanthanum zirconate powder were prepared by rare earth doping modification method.A novel granulation process of the lanthanum zirconate powder was studied.The effects of atmospheric plasma spraying parameters on the properties of coatings were studied by orthogonal method.And systematically studied the influence of rare earth doping on various performance index of lanthanum zirconate ceramics from the study on coating properties,thermal insulation,thermal shock resistance,corrosion resistance and so on.The main conclusions are as follows:1.The La_2-xSm_x(Zr_0.7Ce_0.3)₂O₇ and La_2-2xCe_xCa_x(Zr_0.7Ce_0.3)₂O₇ were synthesizedby co-precipitation method,with the single pyrochlore structure and about 100 nm of the grain size.Compared with yttrium stabilized zirconium,lanthanum zirconate base powder had better high temperature phase stability.Comparing the thermal properties of different doping ratio of Sm in La_2-xSm_x(Zr_0.7Ce_0.3)₂O₇,the thermal expansion coefficient?TEC?La_1.6Sm_0.4(Zr_0.7Ce_0.3)₂O₇?LSZC?was the highest,about 10.46×10^–6 K^-1 at 1450°C,the thermal conductivity was 0.781 W·m^-1·K^-1,which was the best value of of all the previous studies.The thermal expansion property of La_1.2Ce_0.4Ca_0.4(Zr_0.7Ce_0.3)₂O₇?LCCZC?was best through theoretical analysis,which was 12.34×10^–6 K^-1 at 1450°C,which was the best value of of all the previous studies.The thermal conductivity of LCCZC was 1.165W·m^-1·K^-1.2.Three kinds of spray granulation method for LZ spraying powders were researched by particle size test,morphology characterization,fluidity test and loose density detection.The results indicated the powders prepared by new gel spray granulation had the best properties.This method removed the plasma spherification process compaired with the traditional nano powder spray granulation,and enhanced the density and mobility of the powders compaired with the dry gel with ball milling spray granulation.The LZ series spraying powders prepared by gel spray granulation keep the single pyrochlore structure,with the spherical particle size of 60?m,grain size of 100²00 nm,density of 2.2 g/cm³and mobility of 35 s/50g.3.The technological parameters of the Air Plasma Spraying?APS?for the NiCoCrAlY bond layer and top layer was explored by the orthogonal experiment.The best technological parameters of the bond layer was the spraying power of 40 kW,spraying distance of 120 mm,spraying speed of 100 mm·min^-1 and spraying times of 1;The best technological parameters of the top layer was the spraying power of 48 kW,feeding voltage of 9 V,spraying distance of 120 mm and spraying speed of 200 mm·min^-1.Three kinds of lanthanum zirconate based TBCs was prepared by the optimum parameters,with the thickness of about 270?m.The phase kept the pyrochlore structure and had high temperature phase stability from XRD and TG results.The bonding strength of LZ,LSZC and LCCZC TBCs prepared by the best technological parameters were48.29 MPa,50.41 MPa and 48.28 MPa respectively,all of them meeting the current requirements for the bonding strength of TBCs.4.The thermal insulation property of different TBCs was tested by using the self-designed thermal insulation test equipment.The thermal insulation property of doped LZ was obviously improved,where the thermal insulation property of LSZC was the best,the thermal insulation temperature about 250°C.The thermal shock resistance property of different TBCs was researched according to industry standards.The thermal shock resistance property of doped LZ was obviously improved,where the number of thermal shock failure of LCCZC was 115,about 2.5 times of LZ's thermal shock failure number.Microcrack propagation and TGO growth are the root causes of thermal shock failure.5.The CMAS corrosion resistance of different coatings was investigated by simulating the corrosive environment in practical applications.The LZ series TBCs could resist the CMAS corrosion for the formation of the Apatite structure.The CMAS corrosion resistance of LSZC and LCCZC were better than that of LZ,where the corrosion depth were 9?m,10?m and 14?m for them respectively in 1250°C for 4 h.It is mainly because the smaller ion radius of lanthanide is more likely to react with CMAS corrosion.When the temperatue was 1300°C,the corrosion depth become larger,which suggested the temperatue was an important factor for CMAS corrosion.The corrosion failure of the lanthanum zirconate based TBCs was studied.The molten CMAS reacted with the TBCs materials in the surface or the crack of the TBCs,and then the TBCs materials decomposed and the corrosion depth become larger,where the strain tolerance was reduced and causing the destruction of TBCs.