Influence Of Yttria Stabilised Zirconia As Diffusion Barrier On Interdiffusion Between MCrAlY And Ni-base Single Crystal Superalloy

The combination of Ni-base single crystal superalloy with excellent high-temperature mechanical performance and MCrAlY(M is Ni and/or Co) with outstanding high-temperature anticorrosion performance can greatly increase the blade working temperature, and then the efficiency of advanced aeroengine and gas turbine. However, the interdiffusion between MCrAlY coating and Ni-base single crystal superalloy makes the service life of MCrAlY coating substantially reduce; moreover, the secondary reaction zone (SRZ) formed by interdiffusion makes the creep fracture life of Ni-base single crystal superalloy obviously reduce. The diffusion barrier (DB) fabricated between coating and substrate has been an effective way to solve this problem in some degree while the active DB possesses an excellent interdiffusion blocking effectiveness and good adhesion with coating and substrate.The electron beam physical vapour deposition (EB-PVD) technology was employed to fabricate an yttria stabilised zirconia (YSZ) DB between Ni-base single crystal superalloy and multi-arc ion plated NiCrAlY coating. The interdiffusion behavior of NiCrAlY coating, the effectiveness of YSZ DB and its influence on the oxidation performance of NiCrAlY coating were investigated with scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrum (EDX), X-ray diffractometer (XRD), electron probe microanalysis (EPMA) and transmission electron microscopy (TEM). The results were summarized as following:The Cr(Re, W)-rich precipitate layer, interdiffusion zone (IDZ) and SRZ from top to bottom were formed due to the interdiffusion between the NiCrAlY coating and the Rene N5 substrate in the four groups of experiment:isothermal oxidation at 1000 ℃ for 1000 h and at 1100 ℃ for 200 h, and cyclic oxidation at 950 ℃ for 1000 h and at 1050 ℃ for 300 h. However, for the YSZ+NiCrAlY coating, the YSZ DB reacted with the element Al from the NiCrAlY coating and the substrate to form two continuous, compact and straight layers of α-Al2O3 at both the interfaces of NiCrAlY/YSZ and YSZ/N5, respectively, which effectively blocked the interdiffusion between the coating and the substrate. The interface between the YSZ layer and the inner α-Al2O3 layer cracked locally after 1000 h cyclic oxidation at 950℃ while all the interfaces of the inner and outer α-Al2O3 layers remained excellent adhesion in the other three groups of experiment. In addition, in the four groups of experiment, the YSZ+NiCrAlY coating had better high-temperature antioxidation performance than the NiCrAlY coating did, the reasons of which might be that the YSZ layer effectively blocked the diffusion of the third element Cr, good for antioxidation, to the substrate and the counter-diffusion of the elements W, Ta, etc., bad for antioxidation, to the coating.A nanocrystalline layer of Ni3(Al, Hf) was prepared by magnetron sputtering between the YSZ layer and the N5 substrate to solve the local cracks between the YSZ layer and the inner α-Al2O3 layer. The Ni3(Al, Hf) layer could make the YSZ layer form two continuous, compact and curve layers of α-Al2O3 beside the YSZ layer with the almost same thickness, respectively, which effectively blocked the interdiffusion between the coating and the substrate in the two groups of experiment:isothermal oxidation at 1000℃ for 1000 h and cyclic oxidation at 950℃ for 1000 h. Moreover, all the interfaces of the inner and outer α-Al2O3 layers remained excellent adhesion in the two groups of experiment. There were no difference between the Ni3(Al, Hf)+YSZ+NiCrAlY coating and the YSZ+NiCrAlY coating for antioxidation performance, but the Ni3(Al, Hf) layer overcame the local cracks between the YSZ layer and the inner α-Al2O3 layer.In contrast to the NiCrAlY/N5 system, only the IDZ and SRZ were formed from top to bottom due to severe interdiffusion between the NiCrAlY coating and the DD6 substrate. The same as the NiCrAlY/N5 system, the YSZ DB reacted with the element Al from the NiCrAlY coating and the substrate to form two continuous, compact and straight layers of α-Al2O3 at both the interfaces of NiCrAlY/YSZ and YSZ/N5, respectively, which effectively blocked the interdiffusion between the coating and the substrate, and increase the high-temperature antioxidation performance of the NiCrAlY/DD6 system. In addition, the thinner YSZ layer favoured the less consumption of the element Al from the NiCrAlY coating, but its influence on the interface adhesion needs further research.