Fabrication of AlCoCrFeNi High Entropy Alloy via Binder Jetting and Direct Energy Deposition: Characterization, Microstructural Modification, and Analysis

Additively manufactured high entropy alloys are in the early stage. More studies are required on how their compositions, processing routes, and microstructural evolutions intertwine to influence their (mechanical) properties for various fields of applications. In this study, the equiatomic AlCoCrFeNi high entropy alloy was fabricated via two additive manufacturing routes: binder jetting (3DBJ) and direct energy deposition (DED). The response of the samples to isothermal heat treatment was investigated and compared with the as-printed samples. The microstructural evolution was studied using backscattered electrons images from scanning electron microscopy (SEM). Energy dispersive spectroscopy (EDS) was used to probe the constituent’s composition/distribution. The different phases present in the microstructure were investigated using X-ray diffractometer (XRD) and electron-backscattered diffraction (EBSD) techniques. Moreover, the mechanical properties data captured via nanoindentation were evaluated and mapped to show a representation of how they vary through the bulk alloy. Interplays of these essential parameters are responsible for the various mechanical properties exhibited by the alloy. The isothermal heat treatments significantly modified the microstructures of the alloy. However, the 3DBJ and DED samples respond differently, as diffusion mechanisms like grain boundary precipitation, precipitate-free zones (PFZ), and widmanstatten structure were more observable in the 3DBJ samples. The 3DBJ samples exhibit higher values of mechanical properties than the DED samples. The higher mechanical properties in 3DBJ samples are also linked to intermetallics such as sigma phase and ordered BCC (B2). Consequently, the effects of these phenomena are summarized by the difference between the properties of the as-printed samples (2 - 13 GPa hardness, 130 - 240 GPa reduced modulus) and those of the heat-treated samples (4 – 8 GPa hardness, 160 – 200 GPa reduced modulus). The ongoing exploits provide significant insight into how to exploit the immense opportunities AlCoCrFeNi high entropy alloy has for fields of applications such as the tools, automobile, structures, and aerospace industries.