Wear and Corrosion Resistant Eutectic High-Entropy Alloy Al0.3CoCrFeNiMo0.75 Produced by Laser Metal Deposition and Spark-Plasma Sintering

Abstract

Eutectic high-entropy alloys (EHEAs) with a fine-lamellar structure and homogenous property profile are of particular interest for wear and corrosion protection coatings. High cooling rates in the laser metal deposition (LMD) process can induce microstructure refinement and allow the formation of a supersaturated solid solution in EHEAs. A subsequent solution annealing can create the equilibrium state. In the present study, LMD coatings with an ultrafine-grained Widmanstätten structure were produced from the EHEA Al0.3CoCrFeNiMo0.75 gas atomized powder. High cooling rates during deposition led to a supersaturated solid solution with face-centered cubic (FCC) structure. The LMD coating exhibits the highest average hardness of 734 HV0.5, which drops to approx. 200 HV0.5 due to an increased microstructural domain size after heat treatment. Under oscillating wear, the formation of oxidized wear debris promotes material removal in the heat-treated condition. Corrosion tests reveal a deterioration of the passivation behavior. LMD processes exhibit great potential to create supersaturated solid solutions with refined structure in EHEAs to enhance the property profile.