Influence Of Novel Diffusion Barriers On The Interdiffusion Behavior Of NiAlHf/Ni-based Superalloy Systems

When nickel-based single crystal superalloys are used as the base materials of aero-engine blades,it is usually necessary to add a high-temperature protective coating to meet the working temperature requirements of the blade.However,due to the difference of element composition,the inter-diffusion behavior of elements will inevitably occur between the coating and the alloy substrate under high temperature conditions.The inter-diffusion of elements will not only greatly reduce the oxidation resistance of the coating,but also cause the formation of an inter-diffusion zone(IDZ)and a secondary reaction zone(SRZ)in the alloy substrate,and the precipitation of topological-close-packed(TCP)harmful phases,which will be serious Affect the mechanical properties of superalloys.Adding a diffusion barrier between the coating and the substrate is the most direct and effective way to solve the above problems.Therefore,this papers mainly focuses on the influence of new diffusion barriers such as AlTiCrNiMo,Al Co Cr Ni Mo high-entropy alloy(HEA)and Cr Si₂on the inter-diffusion behavior of elements between the coating and the substrate and the oxidation resistance.In this paper,the second-generation nickel-based single crystal superalloy(N5)is selected as the substrate,and the AlTiCrNiMo,Al Co Cr Ni Mo and Cr Si₂diffusion barriers are prepared on the surface of the N5 substrate by magnetron sputtering technology,and then the arc ion plating technology is used to depositing substrate NiAlHf high temperature protective coating.Using X-ray diffractometer(XRD),electron probe microanalysis(EPMA),scanning electron microscope(SEM),transmission electron microscope(TEM)and other experimental methods,combined with Hit.DIC diffusion simulation analysis,different diffusion in high temperature environments are studied.The influence of barriers on the inter-diffusion behavior of elements between the coating and the substrate.At the same time,the anti-oxidation performance is compared through the constant temperature oxidation test.The main findings are as follows:(1)In order to overcome the problem of insufficient chemical matching between the traditional metal diffusion barrier and the coating and the alloy matrix,AlTiCrNiMo high-entropy alloy(HEA)is used as a diffusion barrier material.Under the condition of static isothermal oxidation at 1100?,the effect of AlTiCrNiMo on the inter-diffusion behavior of elements and high temperature oxidation resistance of the coating system was studied.The results show that after 100 h of oxidation,the IDZ+SRZ depth of the alloy substrate is reduced by 10?m compared with the system without diffusion barrier,and there is no?'-Ni₃Al"poor aluminum channel"in the NiAlHf coating,indicating that the AlTiCrNiMo high-entropy alloy It can effectively inhibit the inter-diffusion of elements between the coating and the alloy substrate.In addition,the massive Laves C15 phase precipitates in the NiAlHf coating,but there is still a rod-like or needle-like TCP harmful phase(?phase).This is because Ti promotes the transformation of?phase to?'phase to form a precipitated phase.After oxidization for 300 h,the amount of oxide scale per unit area of the coating was 10.21 mg/cm²,which was reduced by23%.(2)In order to further improve the diffusion resistance effect of the high-entropy alloy,the Ti element is replaced with the Co element,and the Al Co Cr Ni Mo high-entropy alloy layer is selected as the diffusion barrier.The results show that the coating system containing Al Co Cr Ni Mo high-entropy alloy diffusion barrier has no IDZ and SRZ regions,no needle-like or rod-like TCP harmful phases are precipitated during the constant temperature oxidation at1100?,and only the massive Laves C15 strengthening phase is precipitated,indicating that the Al Co Cr Ni Mo layer has The excellent anti-diffusion effect is mainly attributed to three aspects:one is the slow diffusion effect of the high-entropy alloy itself to slow down the inter-diffusion of elements;the second is that the diffusion barrier spontaneously forms an Al₂O₃layer during the oxidation process to hinder the inter-diffusion of the elements;the third is the diffusion barrier The Co element in it can stabilize the?/?'phase structure and inhibit the precipitation of harmful phases such as TCP.In addition,after 300 h of oxidation,the amount of oxide scale per unit area of the coating system was 8.03 mg/cm²,which was reduced by 39%.(3)Aiming at the problem of physical mismatch between traditional ceramic diffusion barrier and coating and alloy matrix,Cr Si₂with a thermal expansion coefficient similar to that of the alloy is used as the diffusion barrier to study the interaction of the Cr Si₂diffusion barrier on the N5/NiAlHf system at 1100?and 1200?.Influence of diffusion behavior and antioxidant properties.The experimental results show that after oxidizing at 1100°C for 100 h,compared with the non-diffusion barrier system,there is no?'-Ni₃Al"poor aluminum channel"in the NiAlHf coating containing Cr Si₂diffusion barrier,indicating that Cr Si₂can inhibit the coating of Al Internal diffusion,but the size of the alloy precipitated massive TCP phase(P phase)increased.After 300 h of oxidation,the amount of oxide scale per unit area of the coating system was 7.45 mg/cm²,which was reduced by 43%.After being oxidized at 1200°C for 200 hours,the coating did not form the kirkendall effect,and?-Ni Al phase still exists.The amount of oxide scale per unit area of the coating system was 16.34 mg/cm²,which was reduced by 26%.In summary,the NiAlHf protective coating system with AlTiCrNiMo,Al Co Cr Ni Mo high-entropy alloy and Cr Si₂as diffusion barriers has better oxidation resistance,which proves that high-entropy alloys and Cr Si₂materials have the effect of inhibiting element diffusion.This has a good reference value for the reasonable selection and design of high-entropy alloys and ceramic diffusion barriers.