High-Temperature Oxidation of AlxCoCrFeNi High-Entropy Alloy Bond Coats Deposited using High-Speed Laser Cladding for Thermal Barrier Coatings

摘要

High entropy alloys (HEAs) are being explored as prospective substitutes for high temperature structural components. These HEAs are typically fabricated using conventional techniques like arc melting, mechanical alloying etc., while these routes exhibit a wide range of limitations. The coating surface prepared by ultra -high-speed laser cladding was well formed with dense internal structure, low defects, high bonding strength with the matrix, excellent mechanical properties and corrosion resistanc e. AlxCoCrFeNi (x=0, 0.3, 0.5, 0.7, 1) high -entropy alloys (HEAs) with good high - temperature oxidation resistance were deposited as bond coats by high-speed laser cladding for thermal barrier coatings. The microstructure of the Alx CoCrFeNi bond coats exhibited the columnar-to-equiaxed grain transition with increasing Al content. In the subsequent isothermal oxidation process, the diffusion between the bonding layer and the substrate was controlled at a low level, and the new Al xCoCrFeNi bond coat exhibited excellent oxidation and diffusion resistance. All bond coats generated a uniform and dense aluminum oxide layer and exhibited a low thermally grown oxide (TGO) growth rate after 100 h of oxidation at 1100◦C. FCC and FCC + BCC structures formed for Al 0.3CoCrFeNi and Al 0.7CoCrFeNi alloys with corresponding hardness of 180HV and 380HV. During oxidation, the mass gain for HEA Al 0.3CoCrFeNi was greater than for Al 0.7CoCrFeNi. Each oxidized HEAs formed an extern al Cr2O3 scale with Al2O3 subscale formed beneath. While, the thickness and continuity of oxide layers varied according to Al content. Al enhanced the oxidation resistance of the AlxCoCrFeNi HEAs.