The Effect Of Prepar Ation And Treatment Process Of Bonding Layer On Thermal Barrier Coating Oxidation Behavior

Thermal barrier coatings(TBCs)are widely used in high-temperature hot-end parts of aero-engines and gas turbines to protect them from high-temperature gas,thus protecting the alloy matrix.Thermal barrier coatings are typically bonded by Bond Coat(BC),a thermal insulation layer(Top Coat,TC),and heat generated on the surface of the bonding layer during high temperature service.It is composed of a grown oxide layer(TGO).The composition and thickness of TGO layer determine the size and distribution of stress at the interface of TC/BC,and the preparation and treatment process of bonding layer can significantly affect the structure of TGO layer and determine the growth characteristics of TGO.Air plasma spraying(APS)is widely used because of its advantages such as low cost,high working efficiency and wide adjustable thickness range.On the other hand,it is easy to oxidize the powder during flight due to the high porosity of plasma sprayed coating.It also prompted researchers to look for better spraying technology to replace it.In the process of Detonation-gun spraying(DS),the metal particle temperature is low,the coating is dense and the adhesion is strong,so it has a good potential in the field of thermal barrier coatings preparation.The aim of this theme is to optimize the process parameters of DS NiCoCrAlY bongding layer and determine the optimum oxygen-fuel ratio.Then the NiCoCrAlY bonding layer is prepared by DS and APS,and the YSZ ceramic insulation layer is prepared on it.The high temperature oxidation resistance of thermal barrier coatings under two kinds of bonding layer structures was analyzed.The phase,microstructure and composition of the coating were analyzed by XRD,SEM and EDS.The bonding state of the coating with the substrate and the oxidation resistance at high temperature were also studied.Finally,the vacuum pre-oxidation process of DS NiCoCrAlY coating is optimized to determine the optimal pre-oxidation time,which provides a reference experiment and theoretical basis for improving the high-temperature oxidation resistance of thermal barrier coatings and prolonging its service life.1.The research in the effect of oxygen-fule ratio of explosive spray on the properties of NiCoCrAlY bonding layer.When the oxygen-fule ratio is relatively low,the NiCoCrAlY powder is not sufficiently melted.There is a large amount of pores at the interface with the matrix.With the increase of the oxygen-fule ratio,the porosity of the bonding layer is continuously decreased,and the hardness and bonding strength are obviously improved;when the oxygen-fule ratio is 1.2.The Vickers microhardness HV0.1 of the bonding layer is 936.4 kg/mm2,the porosity is 1.39%,and the bonding strength between the bonding layer and the substrate reaches 62.5 MPa.The oxygen-fule ratio is continuously improved and the mechanical properties of the bonding layer decrease.2.The effect of bonding layer structure on oxidation resistance of thermal barrier coatings was studied.The inner structure of the bonding layer prepared by DS is dense,the defects are few,and the pores in the bonding layer with the matrix are few;while the lamellar characteristics in the bonding layer of APS are obvious,the pores are more,and the surface roughness is lower.A dense oxide film rich in Al2O3 was formed on the surface of the bond layer after 5 h oxidation prepared by DS,while the oxide layer rich in NiO,CoO,Cr2O3 and Ni(Cr,Al)2O4 was formed on the surface of the bond layer deposited by APS,and there are many microcracks and lamellar oxides in it.The oxidation weight gain rate of DS thermal barrier coating samples was higher than that of APS thermal barrier coating samples in the first 5 hours,and then became smooth,while the oxidation rate of APS thermal barrier coating samples was still higher than that of DS thermal barrier coating samples.The thermal growth oxide layer of DS thermal barrier coating is continuous after 50 h oxidation,the thickness is uniform,and the oxide defect in bond layer is less.The microstructure of DS bonding layer is uniform and dense.The powder oxidation and internal oxidation of bonding layer at high temperature are less during spraying,which makes enough A1 to form dense Ak2O3,on the surface of bond coat quickly.The Al2O3 layer with a certain thickness on the surface inhibits the phase diffusion reaction between oxygen and other metal atoms and improves the oxidation resistance of the thermal barrier coating at high temperature.3.Study the effect of vacuum pre-oxidation process of explosive sprayed NiCoCrAlY bonding layer on the oxidation resistance of thermal barrier coatings.After vacuum pre-oxidation,the surface oxidation product of the NiCoCrAlY bonding layer was ?-Al2O3,and its content increased with the increase of pre-oxidation time.When vacuum pre-oxidation for 1 Oh,?-Al2O3 continuously formed on the surface of the bonding layer.Under the same oxidation condition,the weight gain rate of thermal barrier coating after vacuum pre-oxidation for 10 h is lower than that of DS-APS spraying thermal barrier coating.The ?-Al2O3 layer formed by vacuum pre-oxidation has a good high temperature protection effect on the coating.