| The 8YSZ thermal barrier coating(TBCs)has the advantages of high temperature,low thermal conductivity,excellent corrosion resistance and oxidation resistance,but the volume expansion caused by the phase change of 1200 ? is not used in higher temperature conditions,and the new TBCs material are in need of higher and non-phase transition.In this paper,the LMA thick ceramic coating was prepared by using the atmospheric plasma spraying(APS),and the influence factors of the mechanical parameters of LMA coating and their changes were studied,and the relationship between the mechanical parameters and the resistance to thermal shock was studied,and the theoretical basis was provided for the analysis of the failure analysis of the thickness coating thermal shock.Spheric LMA powders with good fluidity and particle size of 25?106?m were prepared by combining high temperature solid phase synthesis and centrifugal spray drying process.LMA coatings with different thickness were prepared by APS process.The 797?m thick LMA coatings were prepared by means of different CPSP(Critical Plasma Spraying Parameter)process parameters,and the phase composition and microstructure of the coating were characterized.The results show that the phase structure of the coating is stable,the interface bonding state of each layer is good,and there is no obvious delamination and peeling.However,with the decrease of CPSP from 1.20 to 0.86,the porosity of the coating increased from 12.14% to 24.88%,which was mainly due to the effect of the decrease of APS spraying power on the melting state of LMA powder.Combined with the mechanical parameter model,the influence rule of mechanical parameters of LMA thick coating was studied,and the thermal shock failure reason of coating was analyzed.With the increase of coating thickness from380?m to 1162?m,the bonding strength decreases from 23.40±3.42 MPa to21.38±2.26 MPa.Based on the model calculation,the residual compressive stress on the coating surface varies from-107.24± 2.74 MPa to-161.18± 2.64 MPa,and the residual compressive stress on the section varies from-64.52± 2.07 MPa to-121.62±6.06 MPa.Under the larger residual compressive stress,the fracture toughness of the coating section is smaller than that of the surface,which reduces the fracture toughness of the coating at the TC/BC interface.The results show that the influence of thickness variation on the coating stress is relatively great.By contrast,with the decrease of CPSP from 1.20 to 0.86,the bonding strength of the coating decreased from 15.98±0.36 MPa to 4.87±0.7 MPa,and the residual compressive stress on the coating decreased from-162.10±12.13 MPa to-93.49±3.28 MPa.The residual compressive stress of the section decreases from-116.02±5.92 MPa to-70.68±3.99 MPa.The thermal shock resistance life of the LMA thick coating at 900? increased with the decrease of CPSP,which was mainly attributed to the decrease of residual stress in the coating.Thus,the thermal cycle life of the LMA thick coating at 900? increased from 2571±245 times to 3394±78 times.In addition,due to the presence of a certain amount of amorphous phase in the LMA coating,the volume shrinkage of the coating is obvious in the range of 800??900? and1100??1200?.Therefore,the volume shrinkage caused by the recrystallization of the amorphous phase of the coating in the process of high temperature thermal shock resistance is also an important factor for the failure of the coating. |
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