Microstructure And High-temperature Oxidation Properties Of NiCoCrAlYSiHf Coating By Arc Ion Plating Under High Current Pulsed Electron Beam

Thermal barrier coatings（TBCs）technology,which has been extensively applied in advanced aviation,navigation,and ground engines,is one of the most high-end technologies.Increasing of service temperatures of aerospace engine puts forward higher requirements on the preparation and performance of TBCs.High-temperature oxidation performance is one of the important bases for judging the service life of TBCs,and it is also an indicator for testing the basic properties of coatings.The MCrAlYX coating is often used as a bond coat layer of thermal barrier coatings,because of its good resistance of high temperature oxidation and hot corrosion.In the high temperature environment,a layer of thermally growth oxide（TGO）is formed on the surface of the MCrAlYX.The uncontrollable growth of TGO is a key factor for the failure of the TBCs system.The growth and evolution behavior of TGO is closely related to the microstructure,phase structure and grain size of MCrAlYX coating.In this paper,the surface microstructure NiCoCrAlYSiHf coating prepared by arc ion plating（AIP）method was irradiated by high-current pulsed electron beam（HCPEB）,in order to realize the control of growth and evolution behavior of TGO,and improve the high temperature oxidation resistance of TBCs.The X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）and three-dimensional laser scanning microscopy（3D-LSM）were used to characterize the microstructure,phase structure and surface topography evolution of the coating.In order to develop a new method to prepare TBCs with improved high-temperature oxidation resistance,the relationship among the surface microstructure of the irradiated NiCoCrAlYSiHf,controlled grown of TGO,and high temperature service performance was established.This research provides a reliable technical route for improving the stability and predictability of MCrAlYX and TBCs coatings.Microstructure analysis showed that the AIP deposited NiCoCrAlYSiHf coating was featured by a large number of stacking particles with different sizes.The surface of the coating was rough and uneven,and a large number of island clusters were distributed.The coating was composed of equiaxed crystals with unequal size,and its phase composition was composed ofγ/γ’,β-NiAl,and NiCoCr phases.After HCPEB irradiation,the surface of AIP-NiCoCrAlYSiHf coating became smooth and dense under the effect of remelting.The surface of the coating was purified,and the uniformity of the composition was improved.The thickness of the remelted layer was gradually increased with the increasing number of irradiation.After 30-pulsed irradiation,the remelted layer was composed of columnar crystals,and a large number of Y₂Al nano-particles and high density of dislocations were formed on the surface of the remelted layer.The high-temperature of oxidation at 1050^oC revealed that after 2h high temperature oxidation,theβ-NiAl phase in the AIP-NiCoCrAlYSiHf coating was reduced.A very thin TGO layer with uneven thickness was formed,which mainly composed ofα-Al₂O₃ and a small amount of mixed oxides.The internal oxidation occurred in large particle regions.After 20h oxidation,theβ-NiAl phase disappeared.The thickness of TGO was increased,and steady-state and metastable Al₂O₃ were present on the TGO surface.After 50h high temperature oxidation,the TGO was porous and with complex constituent.The cracks appeared around the protrusion region,and some regions began to peel off.After 100 hours of oxidation,parts of TGO protrusions were spalled,and the internal oxidation was exacerbated and spreaded into the interior of the coating.After high-temperature oxidation for 200h,the phenomenon of large exfoliation occurred on the surface of TGO and left some pits.The TGO was very loose and composed of mixed oxide.Severe internal oxidation occurred,and the coating was completely ineffective.The high temperature oxidation process of the coating can be roughly divided into three stages:the first stage:the rapid oxidation stage,in which the oxide film was thickened significantly,and the oxidation weight gain rate of the coating was large.The second stage:the oxidation slowing stage,the oxidation weight gain rate of the coating was slowed down.The third stage:the complex oxidation stage,the oxidation weight gain rate of coating increased faster,and the oxidation kinetic curve showed an accelerated upward trend.In contrast,after the NiCoCrAlYSiHf coating irradiated by 30 pulses irradiation,a very thin oxide film which was mainly composed of Al₂O₃ on the remelted layer was formed after 2 hours oxidation.With the extension of oxidation time,the mono-layered Al₂O₃ became more continuous and dense.The thickness of TGO was gradually increased,but its growth rate was rather slowly.Until oxidation for 200hours,the TGO of irradiated coating was still composed of single Al₂O₃.At this moment,the thickness of TGO was only 3μm.Besides,there is no any traces of internal oxidation appeared.The kinetic curve of oxidation of AIP-NiCoCrAlYSiHf coating after HCPEB treatment was approximately parabolic.The irradiation effect induced by HCPEB was beneficial to the rapid formation of oxide film,the slow growth of TGO and oxidation weight gain.The oxidative weight gain and oxide film increase of the treated coating were much less than the original coating.The irradiation effects induced by HCPEB irradiation can provide good conditions for the rapid formation and steady growth of TGO,and the high temperature oxidation resistance of MCrAlY coating can be significantly improved.