Microstructure Evolution and Wear Resistance of the Eutectic High-Entropy Alloy Al0.3CoCrFeNiNb0.5 Produced by Laser Metal Deposition

Eutectic high-entropy alloys (EHEAs) are characterized by a fine lamellar microstructure. This allows for homogeneous functional surface properties. Furthermore, the risk of coarse precipitate formation during coating processes from the liquid state is avoided. However, the influence of the size and the texture of the local microstructure domain on functional properties is still unknown. The present work is devoted to the microstructural evolution of the EHEA Al0.3CoCrFeNiNb0.5. Inert gas atomized powder was processed by laser metal deposition (LMD) and spark plasma sintering (SPS). Both specimens were heat treated near their liquidus temperatures. The different production routes have a decisive influence on the orientation of the lamellar structure. The SPS bulk material has a statistically distributed orientation of the lamellae defined by the microstructure of the powder. However, the remelting of the powder during the LMD process causes a directional vertical solidification of the lamellar structure. Based on these differences, positive effects on their functional properties were detected for directionally solidified LMD coatings. As a result of the heat treatment, the influence of the lamellar orientation on their tribological properties is reduced, whereas the influence of the lamellar size on their property profile can be derived.

Automated summary

The microstructural evolution of high-entropy alloys during different preparation processes was investigated. It was found that the lamellar structure in laser metal deposition (LMD) coatings showed vertical solidification due to the remelting of powder, while the lamellar orientation in spark plasma sintering (SPS) materials was determined by the microstructure of the powder. The LMD coatings exhibited improved functional properties compared to the SPS materials. The influence of lamellar orientation on tribological properties was reduced after heat treatment, and the influence of lamellar size on material properties could be derived.