| Thermal Barrier Coatings?TBCs?are composed of a superalloy substrate,a bond-coat?BC?and a top-coat?TC?.The currently widely used thermal barrier coating ceramic material is 8 wt%yttria-stabilized zirconia?8YSZ?,which has a low thermal conductivity?0.69-2.4 W/?m·K??1273 K??,high strength and fracture toughness(1.33.2 MPa·m1/2).However,at temperatures above 1100?,higher oxygen diffusion rates in the ceramic layer results in accelerating oxidation of the metal bond coat and mismatching in the lattice parameters of the YSZ/thermally grown oxide?TGO?interface.In addition,When the corrosive environment is calcium magnesium aluminum silicon?CaO-MgO-Al2O3-SiO2,CMAS?above 1170?,the phase change due to the absence of yttria in the YSZ coating,which causes cracks and premature flaking.Its application in higher temperature and more complex environments were limited.In this study,La2Zr2O7?LZO?material was used for high temperature insulation,oxygen impermeability and reaction with CMAS to form apatite phase sealing layer slowing down the characteristics of molten salt penetration.The bond-coat was sprayed by D-Gun and LZO/8YSZ double ceramic thermal barrier coatings were prepared by APS.The double ceramic thermal barrier coatings of isothermal oxidation,thermal shock and CMAS corrosion properties were carefully studied.The LZO/8YSZ double ceramic TBCs'mechanism in slowing the oxidation of the bond-coat and effectively impeding the penetration of CMAS were revealed.It provided a data reference for designing long-life LZO/8YSZ double ceramic thermal barrier coatings.The oxidation properties of the LZO/8YSZ double ceramic TBCs were characterized by isothermal oxidation test at 1100?.The inhibition mechanism of the oxygen resistance of LZO on the oxidation of bond-coat was revealed.The results showed that there were no obvious phenomena such as strip oxides and voids in the bond-coat of the LZO/8YSZ double ceramic TBCs.The relative oxidation gain was2.82 mg/cm2,lower than that of the 8YSZ single ceramic TBCs'3.13 mg/cm2.There was no obvious stratification in TGO?the lower layer was Cr 2O3,NiO and?Ni,CO??Cr,Al?2O4 spinel oxides?and the growth rate was 5.79×10-2?m-2/h.And the thickness was 3.75-5.25?m.Lower than that of the 8YSZ single ceramic TBCs'the growth rate(6.26×10-2?m-2/h)and the thickness?5-5.5?m?.That is to say,the LZO/8YSZ double ceramic TBCs showed the characteristics of low growth rate of TGO,small thickness,less mixed oxides such as spinel,and slowy?phase transition rate in the bond-coat.Finally decreasing the oxidation rate of the bond-coat,and has the better oxidation resistance than the 8YSZ single ceramic TBCs.The thermal shock properties of the LZO/8YSZ double ceramic TBCs were characterized at 1100?thermal shock test.The failure number,failure position and failure mechanism of the double layer structure were studied.The results showed that the shock times of the LZO/8YSZ double ceramic TBCs in 1100?were 15 times,and the main failure modes were the layer separation at the center of LZO layer and shedding of the interface between 8YSZ and bond-coat near the 8YSZ side.Its shock times were less than 27 times of the 8YSZ single ceramic TBCs,which is mainly caused by the stress concentration leading the mismatch of thermal expansion coefficient under LZO alternation and the low brittleness of LZO material itself.The corrosion properties of LZO/8YSZ double ceramic TBCs were characterized by 1250?CMAS corrosion test.The reasons for LZO sealing protection were clarified.The results showed that the phase of LZO/8YSZ TBCs reaction layer was dominated by spherical ZrO2 and rod-like Ca2La8?SiO4?6O2,with a small amount of CaAl2Si2O8 and MgAl2O4.The corrosion depth was about 55?m,accounting for 50%of the entire LZO layer.The 8YSZ TBCs became a loose structure mainly composed of spherical m-ZrO2,and the corrosion depth was about 300?m?the entire 8YSZ layer?.The hardness of the 8YSZ and LZO reaction layers increased after corrosion,but the increased in-plane stiffness did not cause delamination cracking at the corrosion interface.As a sacrificial protective layer of double ceramic TBCs,LZO ceramic layer relied on the reaction of La with CMAS to form a dense apatite?Ca2La8?SiO4?6O2?,which effectively reduced the infiltration of CMAS and inhibited the instability of internal 8YSZ. |
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