In-situ alloying of metal particle-reinforced CoCrNi medium-entropy alloy via laser powder bed fusion

Abstract

Medium-entropy alloys (MEAs) have emerged as a promising class of materials, offering a unique combination of superior mechanical properties over their conventional counterparts. This study explores the development of metal particle-reinforced CoCrNi medium-entropy alloys (MPR-MEAs) with in-situ alloying by using laser powder bed fusion (LPBF) on mixed elemental powder blends. By optimizing the LPBF process parameters, a homogeneous distribution of incompletely melted Cr particles is achieved within the CoCrNi matrix, resulting in high-strength MPR-MEAs. The as-built CoCrNi MPR-MEA exhibits a tensile strength of approximately 734 MPa, which is nearly three times that of the as-cast CoCrNi MEA, while still maintaining an elongation of 15 %. The remarkable increase in strength is attributed to the synergistic effects of grain boundary strengthening, thermal mismatch strengthening, and dislocation strengthening. The fracture behavior is characterized by a combination of brittle and ductile modes, with microcracks nucleating from the interior of the incompletely melted chromium particles. Importantly, the chromium particle-matrix interface exhibits no signs of cracking, indicating an excellent metallurgical bond, which does not act as a crack initiator. This study demonstrates the potential of LPBF in-situ alloying for fabricating high-strength MEA composites, providing valuable insights into the design and optimization of advanced metal matrix composites for engineering applications.