EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

High entropy alloys (HEA) are a new class of promising materials with very interesting properties. These alloys have particular and sometimes unstable microstructures. Using additive manufacturing (AM) processes for shaping these innovative alloys allows mastering their microstructures through the versatility and the flexibility of these processes. The AM processes like the laser powder bed fusion (LPBF) uses, generally, powders produced by atomization with excellent physical properties such as flowability, sphericity, etc. However, the elaboration of powders by atomization with particular chemical compositions is difficult and sometimes impossible.
In this study, two powders obtained by two elaboration processes; atomization and mechanical alloying, were used to produce Al-containing CoCrFeNi HEA samples by LPBF process. Firstly, both pre-alloyed powders were characterized. Then, the effects of LPBF energy parameters on the porosity, microstructure and mechanical properties were investigated to define the optimal process parameters. Finally, the part densities obtained by both powders were confronted for different process parameters.
Results show that laser power and scan speed involved in volumetric energy density (VED) plays a significant role in the densification behavior. Parts made using atomized powder are denser than those produced from mechanical alloying powder. The Al-containing CoCuFeNi HEA with full density (obtained by the optimal process parameters) exhibited superior mechanical properties in comparison with as-cast or wrought counterparts.
To conclude, despite its homogeneous chemical composition, the mechanical alloying HEA powder exhibits insufficient morphological properties to be used in LPBF. The flowability and the sphericity must be specifically improved to obtain results comparable to those of atomized powders.