A research team has developed a novel bond coat material that significantly improves the oxidation resistance of thermal barrier coatings (TBCs) at 1,200°C, a critical advancement for next-generation ultra-high-thrust aero-engines.

The study was published in Advanced Science on February 6.

As modern aviation engines strive for higher thrust-to-weight ratios and greater thermal efficiency, turbine inlet temperatures are expected to surpass 1,900 °C, which is well beyond the melting point of superalloys. TBCs are thus essential, serving as thermal insulating ceramic layers on turbine blades. The bond coat, situated between the ceramic topcoat and the superalloy substrate, plays a pivotal role. It must accommodate thermal stress and, critically, form a slow-growing, adherent thermally grown oxide (TGO) layer to protect the substrate from oxidation.

Since the 1970s, NiCoCrAlY (MCrAlY) alloys have been the standard bond coat material. However, they face a major limitation: oxidation rates skyrocket above 1,100 °C, leading to rapid TGO growth and spallation, which causes TBC failure. This temperature ceiling has persisted for decades, hindering engine progress.

To overcome this constraint, the researchers from the Institute of Metal Research of the Chinese Academy of Sciences, Peking University, and Shenyang University of Technology developed a dual strategy focusing on both the initial and steady-state oxidation stages. 

First, the researchers engineered an alloy with a fine lamellar microstructure by optimizing eutectic aluminum content. This enhances aluminum supply during early oxidation, promoting the rapid formation of a continuous, protective α-Al₂O₃ scale. Second, they adjusted the ratios of cobalt (Co), chromium (Cr), and nickel (Ni) to maximize configurational entropy, creating a multi-principal element alloy (MPEA). The resulting severe lattice distortion in the aluminum-depletion zone beneath the TGO increases vacancy formation energy and raises the energy barrier for aluminum diffusion, effectively slowing down the oxidation process at high temperatures.

The developed NiCoCrAlYHf MPEA demonstrated exceptional performance. In 500-hour isothermal oxidation tests at 1,200 °C, its oxidation rate constant was only 1.28×10⁻¹² g²·cm⁻⁴·s⁻¹, approximately 59% lower than that of the traditional MCrAlY alloy. More importantly, in cyclic oxidation tests, the traditional alloy suffered oxide scale spallation after only 70 hours and showed more than 40% surface area loss after 500 hours. In contrast, the new alloy exhibited less than 2% spallation throughout the entire test, demonstrating excellent scale adhesion and spallation resistance.

This breakthrough provides a crucial foundation of materials and a new design paradigm for developing bond coats that can operate in extreme environments, paving the way for future high-performance engines.