Enhancing mechanical properties of CoCrNi via in-situ alloying with Al2O3 through laser powder bed fusion

• In situ alloying of MEA metal matrix composites was achieved via the LPBF technique. • Nanoscale precipitates were refined within the cellular structure of LPBFed MEA. • Precipitates bonded to the matrix, blocking dislocations and improving strength. For advantages in integrating the intrinsic properties of the metal matrix and reinforcing phases, properly designed metal matrix composites (MMCs) are promising candidates for overcoming the trade-offs of properties such as corrosion, ductility, strength, and lightweight. However, MMCs often face challenges such as agglomeration and inhomogeneous distribution of the reinforcing phase, leading to significant degradation of mechanical properties. In this study, we propose a method to overcome these obstacles by in-situ alloying via laser powder bed fusion (LPBF), achieving a uniform distribution of the reinforcing nano-sized phase (α-Al 2 O 3 ) within a medium-entropy alloy matrix (CoCrNi). During the LPBF process, Al 2 O 3 is refined from the micrometer scale to the nanometer scale, simultaneously affecting the crystal orientation and leading to grain refinement of the CoCrNi matrix. The mechanical properties of CoCrNi were significantly enhanced by adding Al 2 O 3 , with an ultimate compressive strength of ∼1143 MPa, a fracture strain of ∼25%, and a hardness of ∼300 HV. The achieved strength and hardness levels are among the highest reported in the literature. The results from this study provide new design strategies for the in-situ formation of MMCs, offering a promising approach to developing MMCs with high strength and ductility.