Interdiffusion Behaviour Of MCrAlY Coating And Single Crystal Superalloy

Single crystal superalloys must be used with high temperature protective coatings to improve their performance and lifespan when they are used for long periods of service.The huge differences in chemical compositions between coating and underlying substrate can lead to element interdiffusion during long-term high-temperature service,resulting in the segregation of insoluble elements in the substrate and the precipitation of harmful topological close-packed phase.The main components of topological close-packed phases are W,Mo and Re,which are added in the superalloy for strengthening the comprehensive performance of superalloys at high temperature.There is no doubt that the precipitation of harmful topological close-packed phases will not only deplete the refractory reinforcing elements in the substrate but also be the source of rack propagation,resulting in the system failure.Up to now,few reports are available on the interdiffusion between MCr Al Y coating and single crystal superalloy during high temperature oxidation process.In order to clarify the interaction between the coating and the substrate and the element diffusion mechanism at high temperature,it is very necessary to carry out related research.In this paper,the LPPS technique was used to prepare the MCr Al Y coating and the high-temperature oxidation performance of the coating was studied.And then the interdiffusion behavior of MCr Al Y coating between two different single crystal superalloys was studied.The main results are as follows:The NiCoCrAlY coating has good surface integrity,and the main component phase isγ-Ni/γ’-Ni₃Al phase.After NiCoCrAlY coating was subjected to high-temperature oxidation at 1100°C for 150 h,a dense thermally grown oxide layer（TGO layer）was formed on the surface of the NiCoCrAlY coating after oxidation.At this time,the average thickness of TGO on the top layer of the coating is about 3.36μm.After 300 h,the thickness of the TGO layer is about 4.58μm;the thickness of the TGO layer at 600 h has exceeded 6μm,but there are obvious cracks in TGO.The only interdiffusion zone was formed after oxidation for 50 h,while both interdiffusion zone and secondary reaction zone could be observed after oxidation for over 100 h.The thickness of interdiffusion zone and secondary reaction zone is increased with the extension of oxidation time,and the grain growth of topological close-packed phase in the secondary reaction zone is found.Al,Cr and Co in the coating diffuse from the coating to the substrate,while Ni and refractory materials like Ta,Mo,Re and W diffuse from the coating to the substrate.The interdiffusion of coating and substrate leads to the instability ofγ/γ′phase in the substrate,which finally results in the formation of W,Re and Cr-rich needle-like topological close-packed phase in the substrate.The inter diffusion zone（IDZ）and the secondary reaction zone（SRZ）appear when the MCrAlY coated IC21 single crystal superalloy was oxidized at 1150°C for5 h.MCrAlY coating/IC21 single crystal statically oxidized at 1150°C produced two different orientations of the precipitated phases,needle-shaped and bamboo leaf-shaped.The components of the precipitated phase included Re,Mo,Cr,Ni and the chemical compositions were both similar.According to the calculation results of the interplanar spacing,this phase wasμ-TCP phase.