Research On High Temperature Oxidation And Interfacial Failure Mechanism Of Pt-modified Aluminide Bond Coat For TBCs

As the operating temperature of advanced aero-engines has been greatly improved to meet the requirements of higher thrust-weight ratio and flow ratio,thermal barrier coatings(TBCs)are necessarily applied on the key hot-components(e.g.gas turbine blades)to acquire reliable protection and prolonged service life.In practice,although a large fraction of commercial TBCs consists of YSZ ceramic top coat and(Ni,Pt)Al bond coat,there still remain unsolved problems for these TBCs in industrial application.For instance,the thermally grown oxide(TGO)formed between the top coat and the bond coat is associated with severe rumpling and high growth rate,where serious element interdiffusion occurs between the bond coat and the single crystal(SX)superalloy substrate during high-temperature exposure that results in deterioration of mechanical properties of SX superalloy.In order to make contribution and offer solution for the above-mentioned issues,in present study,utilizes a second-generation nickel-based superalloy Rene N5 as the substrate alloy and prepare a series of Pt-modified aluminide coatings.Reactive element modification was employed into(Ni,Pt)Al bond coat to produce slighter TGO rumpling.Pre-oxidation at low oxygen partial pressure was performed on the(Ni,Pt)Al coating samples to avoid the formation of fast-growing θ-Al2O3 in TGO.A Pt-modifiedγ’ bond coat was prepared by precisely controlling Al content in the(Ni,Pt)Al bond coat,in which precipitation of harmful needle-like topologically-close-packed(TCP)phases was inhibited.On top of these Pt-modified aluminide bond coats,YSZ ceramic top coats were deposited by electron beam physical vapor deposition(EB-PVD),where thermal cycling behavior and interfacial failure mechanisms of these TBCs were investigated.The main conclusions of present study are drawn as follows:1.Compared with Hf or Y singular modification,co-modification of Hf and Y could further reduce the oxidation rate of(Ni,Pt)Al bond coat,retard the β→γ’ phase degradation of bond coat,minimize the rumpling extent and residual stress of TGO,enhancing the cyclic oxidation resistance of the TBCs.The reason can be clarified as Hf4+ and Y3+ could simultaneously segregate at the grain boundaries of Al2O3 scale,in which the RE ions interact as ionic clusters and effectively inhibit the outward transport of Al,exhibiting "synergistic effect" of REs.2.Prior to deposition of YSZ,a pre-oxidation treatment of(Ni,Pt)Al bond coat with low atmosphere pressure could completely avoid the formation of θ-Al2O3 during thermal exposure of TBCs,which further decreases thickness and residual stress of the TGO,reduces rumpling of the TGO/bond coat interface,thus benefiting the thermal cycling resistance of TBCs.In addition,the low atmosphere pressure could suppress the formation of θ-Al2O3 and accelerate the θ-to-α transformation during pre-oxidation.The pre-oxidation treatment also changed the failure mechanism of(Ni,Pt)Al TBCs from fracturing at the TGO/bond coat interface to cracking at the TGO/ceramic top coat interface.3.A Pt-modified γ’ aluminide coating was prepared by reducing the A1 content in the(Ni,Pt)Al bond coat,which demonstrated minimal interdiffusion with SX superalloy substrate and completely avoided the precipitation of needle-like TCP phases,where its high-temperature oxidation resistance was comparable to the normal(Ni,Pt)Al coating.Compared with the(Ni,Pt)Al-YSZ TBCs,the Pt-γ’-YSZ TBCs exhibited superior thermal cycling resistance and its failure took place the TGO/YSZ interface,in which pure Pt particles at the TGO/YSZ interface tented to generate micro-cracks and weaken the adhesion of TGO and YSZ.