Boost in mechanical strength of additive manufactured CoCrFeMnNi HEA by reinforcement inclusion of B4C nano-particles

As a way to improve the strength of high-entropy alloys (HEAs), reinforcement by composite fabrication of HEAs has recently been investigated in various ways. In this study, CoCrFeMnNi+B4C (2 wt%) high-entropy composite (HEC) parts were fabricated using the direct energy deposition (DED) process of pre-ball milled powders. The grain growth is severely hindered by B4C nano-particles during the layer-by-layer printing of CoCrFeMnNi+B4C HEC compared to CoCrFeMnNi HEA. In addition, as a collateral effect, the sequence of elemental segregation in the dislocation cellular boundary differs in CoCrFeMnNi HEA and CoCrFeMnNi+B4C HEC. Additional segregation of Cr, Mn, and C elements into the cell boundary has been observed. In fact, unlike the CoCrFeMnNi HEA, the segregation of Cr, Mn, and C provides a presence of carbide-rich regions because of the partial decomposition of B4C nano-particles. Furthermore, the B4C nano-particle promotes the pinning effect of moving dislocation leading to the high dislocation density in the matrix, which contributes the biggest portion of strength reinforcing of CoCrFeMnNi+B4C HEC. Besides, the well-distributed B4C nano-particles boost the final strength of the HEC component by providing an additional dispersion hardening effect. Therefore, by co-activation of various strengthening mechanisms, the CoCrFeMnNi+B4C HEC showed magnificent yield and ultimate tensile strengths of 1024 ± 20 MPa and 1264 ± 16 MPa, respectively, with more than 7% of total elongation, which is much higher mechanical strength than the ones reported in the literature.