Hot Corrosion Resistance Of Plasma Sprayed MCrAlY Bond Coat Irradiated By High-current Pulsed Electron Beam

With the fast development of the gas turbine in the aerospace and marine industries,the prevention and control of high temperature oxidation and hot corrosion is one of the core technologies of hot components.Thermal barrier coatings?TBCs?applied in the substrate surface can prevent or reduce the thermal oxidation damage of hot components.Besides,the hot corrosion problem caused by impurities in the fuel containing Na and S or the aggressive environment also can not be ignored.In this paper,the "HOPE-1" type high current pulsed electron beam?HCPEB?was used as the experimental device to modify the surface of CoCrAlY bond coat prepared by air plasma spraying?APS?.Hot salt corrosion method was used to analyse the hot corrosion behavior of bond coat before and after HCPEB irradiation.The molten salt corrosion test includes two kinds of environments: pure sulfate and sulfate containing Cl-.The composition,phase structure,composition and microstructure of hot corrosion products were systematically characterized by the modern test methods,and the effect of HCPEB irradiation on the corrosion resistance of the coating was analyzed,which provides some theoretical and experimental basis for the process optimization and engineering application of thermal barrier coatings.The APS-MCrAlY bond coat was featured by typical lamellar stacking structures.The surface of the coating was rough and uneven,and there were a large number of defects such as holes,semi-molten or non-molten particles and oxide inclusions.The results of surface modification of HCPEB-MCrAlY bond coat showed that after HCPEB irradiation,the structural defects of the original coating surface were improved,and the surface was remelted and filled with the drum bulge structures connected with each other.The surface of the bulge structure was very compact,and the thickness of the remelted layer and the size of the drum like structure were gradually increased with the increase of irradiated pulses.After 30-pulsed irradiation,a large number of Y-riched Al₂O₃ particles and ultrafine grain structures were formed on the irradiated surface.The experimental results of hot corrosion behavior of the coatings in the molten Na₂SO₄/K₂SO₄?75:25,wt.%/wt.%?at 1050 ? showed that the APS-MCrAlY coating had poor hot-corrosion resistance.The continuous and compact protective TGO failed to be formed at the initial stage of hot corrosion test for 30 min.After the hot corrosion was carried out to 50 h,a loose and porous double layered TGO structure was formed.Simultaneously,the hot-corrosion products produced spallation,which caused serious internal oxidation and sulfuration.In contrast,aftet hot corrosion for 30 min,a protective film of Al₂O₃ was promoted to be formed of HCPEB-MCrAl Y coating.In the later stage of hot corrosion,TGO can be treated as a double barrier formed by Al₂O₃ and CoCr2O4 layers.,and no obvious damage of the corrosion layer was observed after the hot corrosion of 50 h,which indicated that the corrosion resistance of the irradiated coating was improved effectively.The experimental results of hot corrosion behavior of coatings in molten Na₂SO₄/NaCl?75:25,wt.%/wt.%?at 1050 ? showed that a protective TGO layer was also failed to be formed of the APS-MCrAlY coating after hot-corrosion for 30 min.It is worth noting that the Cl-had positive effects on accelerating the corrosion rate.After hot corrosion for 20 h,corrosion products penetrated through the interior of the initial coating,which resulted in serious internal oxidation and sulfidation.In this case,the depth of corrosion layer was 20 ?m.In contrast,for the HCPEB-MCrAlY coating,a dense Al₂O₃ protective film can be formed at the onset of hot corrosion for 30 min.After hot corrosion for 20 h,TGO was comprised of two distinct layers: CoAl2_O4 outside layer and ?-Al₂O₃ inside layer.In this stage,the depth of corrosion layer only had a few ?m.The irradaited effects induced by HCPEB treatment can promote the continuous and compact protective oxide film to be formed rapidly in the initial stage of hot corrosion.With the prolonged reaction time of hot corrosion,this oxide film can effectively prevent the penetration of molten salt,which can effectively improve the corrosion resistance of the coatings.