Toward understanding the microstructure and electrical resistivity of thermal-sprayed high-entropy alloy coatings

High-entropy alloys (HEAs) are a new class of advanced metallic alloys that have received significant attention in recent years due to their stable microstructures and promising properties. However, exploration of the functional properties of these alloys as thermal-sprayed coatings has not been undertaken so far. In the present study, novel equiatomic AlCoCrFeMo, AlCoCrFeMoW, and AlCoCrFeMoV HEA coatings were fabricated using flame spraying to understand the impact of tungsten (W) and vanadium (V) additions in AlCoCrFeMo HEA coatings on microstructure evolutions, phase formations, microhardness, and electrical resistivity. The microstructure revealed the occurrence of mixed oxides and BCC phases, with an apparent porosity range between 2 and 4%. Despite the lower fraction of oxide phases, higher hardness was achieved for AlCoCrFeMoV HEA coatings (714 +/- 64 HV), followed by AlCoCrFeMoW (609 +/- 61 HV) and AlCoCrFeMo (592 +/- 58 HV) HEA coatings. The higher hardness might be attributed to combined interactions of hard oxide phases, solid solution strengthening, and BCC phases. The electrical resistivity values showed a noticeable difference between HEA coatings and control Ni-20Cr coatings, whereby higher electrical resistivity values were achieved for AlCoCrFeMo HEA coatings due to topological lattice distortion and higher oxide fractions. Joule heating testing showed a higher rate of increase in surface temperature for all the HEA coatings than that of Ni-20Cr flame-sprayed coatings for a given electrical power input. The results suggest that the improved electrical properties and heating performance capabilities of flame-sprayed HEA coatings make them an excellent choice for use in high load resistive heating applications.