Design,Preparation,and Properties Of A New AlCoCrFeNi-Based High Entropy Alloy Oxidation Resistant Coating

Thermal barrier coatings are widely used to protect the hot parts of aero-engines and land-based gas turbines,which can significantly improve the thermal efficiency of engine and extend the lifetime of the hot components.Currently,MCr Al Y（M=Ni,Co）or aluminum coatings are the most used thermal barrier coating bond coat.However,interdiffusion between the superalloy substrate and these bond coats occurs at high temperature,resulting in the degradation of the mechanical properties of the superalloy and the oxidation resistance of the coatings.AlCoCrFeNi high-entropy alloys have excellent room temperature ductility and high temperature strength.Protective oxide layers can be formed on their surface during high temperature applications.Besides,the sluggish diffusion effect of high-entropy alloy is expected to suppress the interdiffusion between the coatings and substrates.Therefore,AlCoCrFeNi high-entropy alloys are regarded as very promising materials for bond coat of thermal barrier coatings or oxidation-resistant coatings.It has become the key to extensive research to obtain target alloys with better performance by adjusting the content of each principal component in high-entropy alloys.In this paper,AlCoCrFeNi high-entropy alloys coating with excellent properties were obtained by adjusting the contents of the main elements.AlCoCrFeNi high-entropy alloys with different Al content and Ni content were designed and prepared.The phase composition,microstructure,mechanical properties and oxidation resistance were systematically studied.The specific research contents and results of this paper are as follows:AlxCoCrFeNi high entropy alloy（0≤x≤1.75）and AlxCoCrFeNiy high entropy alloy were prepared by multi-channel powder feeding laser cladding equipment.The phase,macro and microstructure morphology and mechanical properties of AlxCoCrFeNi（0≤x≤0.9）high entropy alloys with different Al contents were analyzed.The results show that with the increase of Al content,the phase transformation from single FCC phase to FCC+BCC dual-phase structure and finally to single BCC phase occurred in the alloy,and the microstructure also produced spinodal decomposition structure with the increase of Al content.With the transformation of phase and microstructure,the hardness of the alloy increased,and the cracking sensitivity of the alloy increased during laser cladding preparation.Isothermal oxidation of the AlxCoCrFeNi high-entropy alloy was conducted at 1100°C for 250 h,and its microstructure changes and oxidation kinetics were observed and analyzed.The analysis results showed that phase transformation occurred for the annealed AlxCoCrFeNi high-entropy alloys with the change of Al content,similar to the as-deposited alloys.After high temperature exposure,the oxide scale on the surface of Fe Co Cr Ni alloy was mainly composed of an outer complex oxide layer and an inner Cr₂O₃ layer.The addition of Al element changed the original oxide layer structure.The outer oxide layer was composed of Cr₂O₃ and complex oxides,and the internal layer was formed by a discontinuous Al₂O₃ oxide layer.With the increase of Al content,the oxide layer was mainly composed of Al₂O₃instead of Cr₂O₃,and the Al₂O₃ oxide layer became more and more continuous and dense,improving the oxidation resistance of the alloys.In order to improve the oxidation resistance of the AlCoCrFeNi high-entropy alloys and reduce the tendency of thermal cracking in the laser cladding process,AlxCoCrFeNiy high-entropy alloy was prepared,and its microstructure and properties were systematically studied.Contrary to the effect of increasing the Al element content on the alloy,the increase of Ni content resulted in the increase of the FCC phase and the ordered BCC phase in the alloy,decreases the disordered BCC phase.The cracks density was largely reduced for the AlxCoCrFeNiy alloy with a high content of Ni.The high-temperature oxidation behavior of AlxCoCrFeNiy alloy and AlxCoCrFeNi alloy was similar,in which the thickness of the oxidation layer changed with time according to a parabolic growth rule.The produce protective oxide layers on the alloy surface were mainly consisted of Al₂O₃ and Cr₂O₃.