Unravelling the Tribological Characteristics of AlCoCrFeMo High Entropy Alloy Coatings Deposited by Different Thermal Spray Techniques

High entropy alloys (HEAs) are advanced materials that possess exceptional mechanical and corrosion properties, enabling their use in aerospace applications. In this study, AlCoCrFeMo HEA was fabricated using cold spraying, flame spraying, and high-velocity oxy fuel spraying to investigate their microstructures, phases, mechanical properties, and sliding wear characteristics. The results showed noticeable increase in hardness for HVOF coatings due to lower porosity, fine microstructure, and oxide inclusions compared to the other two coatings. In terms of the their tribological performance, the cold-sprayed coatings exhibited overall lower frictional coefficient compared to the flame-sprayed and HVOF coatings at different temperature ranges. However, the HVOF coatings exhibited relatively lower wear rates, which correlates well with observations of ex situ analysis, highlighting lower material transfer and a decrease in the formation of debris particles when compared to cold-sprayed and flame-sprayed coatings. Elemental analysis also revealed a stable oxide-based tribofilm on the worn surfaces, which contributed to the higher wear resistance of HVOF coatings at elevated temperatures. These results suggest that HEA materials are promising candidates for next-generation tribological interfaces under these specific conditions of high-temperature wear, pointing to new material designs with improved microstructural features.