Abstract
It has been proposed that multi-principal element (MPEA) system can be explored and produced with readily available commercial alloys through controlled mixing to achieve MPEA compositions. This strategy has the potential to drastically decrease MPEA production costs while facilitating rapid and efficient MPEA composition exploration. In the current work, multi-layer samples of CoCrFeNi base MPEAs were fabricated with directed energy deposition (DED) in both bulk and functionally graded material (FGM) forms to investigate alternative compositional mixtures. Within the FGM, composition was spatially varied from stainless steel 316 L (SS316L) to a CoCrFeNi MPEA. The feedstock materials employed for fabrication included commercially available AMP 750 (CoCr), SS316L and Inconel 718 (IN718). Critical DED processing parameters, such as laser power, powder feed rate, and scan speed, were systematically optimized to achieve the targeted MPEA compositions. Cross-sectional imaging of each sample was performed using laser optical microscopy, and scan-ning electron microscopy (SEM) was used to probe grain size and morphology, as well as interface behavior in detail. Phase analysis was conducted using x-ray diffraction (XRD) for the bulk sample, and each FGM layer. Compositional analysis was performed via energy dispersive x-ray spectroscopy (EDS) on SEM and transmission electron microscopy (TEM) to identify MPEA and potential secondary phases. Nanoindentation measurements were carried out to determine the spatial mechanical properties and these data were correlated with the compositional and microstructural analyses. EDS analysis shows successful mixing of the commercial powders in a 1:1:1 weight% ratio to achieve a Co23.03Cr22.76Fe18.88Ni 22.16Nb1.36Mo2.53 MPEA system