| As an advanced high temperature protective coating,thermal barrier coatings(TBCs)technology is of great importance to high performance aero-engines and gas turbine engines.Nanostructure and rare earth zirconate TBCs are the vital development direction of high performance ultra-high temperature thermal barrier coatings in the future.In this paper,two kinds of nanostructured feedstocks for plasma spraying whose raw materials are zirconia stabilized by 8wt%Y2O3(8YSZ)and La2(Zr0.75Ce0.25)2O7(LCZ)nanopowders were successfully prepared using the nanopowder granulation method.Nanostructured LCZ/8YSZ double-ceramic-layer TBCs,conventional and nanostructured 8YSZ TBCs were designed and fabricated by atmospheric plasma spraying.The formation mechanism,mechanical properties,thermal properties and high temperature CaO-MgO-Al2O3-SiO2(CMAS)corrosion performance of nanostructured TBCs were systematically investigated.As-prepared 8YSZ and LCZ feedstocks are spherical in the shape with smooth surface and dense interior.The feedstocks are in the free flowing state and their particle size meets the requirements of plasma spraying.The grain size of the two kinds of feedstocks remain the nanostructure.The phase structure of nanostructured 8YSZ feedstocks is non-transformable tetragonal phase(t'-8YSZ),and the phase structure of nanostructured LCZ feedstocks is pyrochlore phase(P phase).Three kinds of TBCs were deposited onto K417G superalloy substrate by atmospheric plasma spraying.The microstructure and phase composition of as-sprayed nanostructured TBCs were analysed.Results show that the microstructure of nanostructured 8YSZ coatings and nanostructured LCZ coatings presents bimodal distribution.The growth orientation of columnar nanocrystals in the "splat" of nanostructured 8YSZ coatings is[101]direction.The t' phase in nanostructured 8YSZ coatings is mainly composed of two parts,one is unmelted nanostructured feedstocks,the other is melted t' phase feedstocks experiencing rapid solidification.The growth orientation of "splat" columnar nanocrystals of LCZ coatings is[111]direction.The phase of nanostructured LCZ coatings is fluorite phase(F-LCZ)with a small amount of t-ZrO2,which reveals the in-situ self toughening mechanism of plasma sprayed nanostructured LCZ coatings.The formation process models of two kinds of nanostructured TBCs were constructed.The mechanical properties of TBCs were analyzed by nano indentation technology and tensile strength test.Results show that the elastic modulus and nano hardness of the nanostructured 8YSZ coatings are sensitive to the melted zone,while the elastic modulus and nano hardness of nanostructured LCZ coatings are sensitive to the unmelted zone.The plastic indentation work of conventional and nano structured TBCs is sensitive to microstructure.The ratio of plastic indentation work to total indentation work(MDP)of conventional 8YSZ coatings is 0.58±0.04,MDP value of nano structured 8YSZ coatings is 0.62±0.05,and MDP value of nanostructured LCZ coatings is 0.67±0.04.The bonding strength of nanostructured 8YSZ TBCs and LCZ/8YSZ TBCs are higher than that of conventional 8YSZ TBCs.The bonding strength of nanostructured LCZ/8YSZ TBCs is slightly lower than that of nanostructured 8YSZ TBCs.The strengthening and toughening mechanism of nanostructured TBCs were analyzed.The thermal and CMAS corrosion properties of TBCs were analyzed.Results show that the thermal expansion coefficient of nanostructured 8YSZ coatings is higher than that of conventional 8YSZ coatings,and the thermal expansion coefficient of nanostructured LCZ coatings is lower than that of nanostructured 8YSZ coatings.The thermal conductivity of three kinds of coatings decreases with the increase of the test temperature(from room temperature to 1473K),and the thermal conductivity of conventional 8YSZ coatings is the largest,and the thermal conductivity of nanostructured LCZ coatings is the smallest.The thermal insulation effect of three kinds of TBCs enhances with the increase of test temperature,and the thermal insulation effect of nanostructured LCZ/8YSZ TBCs is better than that of nanostructured 8YSZ TBCs,and the thermal insulation effect of nanostructured 8YSZ TBCs is better than that of conventional 8YSZ TBCs.At 1200?,the thermal insulation temperature is 145K for nanostructured LCZ/8YSZ TBCs,120K for nanostructured 8YSZ TBCs and 90K for conventional 8YSZ TBCs.Nanostructured LCZ/8YSZ TBCs can prevent high temperature CMAS silicate corrosion to a certain extent.However,nanostructured and conventioanl 8YSZ TBCs cannot resist CMAS corrosion,and nanostructure can delay the corrosion rate of CMAS.In the process of high temperature CMAS corrosion,the top layer of LCZ reacts with CMAS to form dense apatite,anorthite and cubic zirconia,which further inhibits the penetration of CMAS,thus prolonging the service life of TBCs.The failure mechanism of conventional and nanostructured 8YSZ TBCs is mainly due to the thermal stress effect of high-temperature CMAS in the penetration process. |
PDF Full Text Request