Strength-ductility synergy of CoCrNi medium-entropy alloy processed with laser powder bed fusion

Abstract

In this work, CoCrNi medium-entropy alloy (MEA) parts were fabricated by laser powder bed fusion (LPBF) with different laser powers. The microstructural evolution before and after tensile test was characterized to explore the strengthening and ductility improvement mechanisms. Similar microstructures and tensile performances were achieved among the samples that were fabricated with different processing parameters, which indicates a credible parameter window for fabricating high-quality CoCrNi samples. An excellent combination of tensile strength and ductility was acquired (yielding strength: 689–700 MPa, ultimate tensile strength: 963–973 MPa, and elongation after fracture: 31.9–37.7%), which were primarily attributed to the grain boundary strengthening mechanism and adequate working hardening capacity, respectively. After tensile test, most grains were rotated by aligning 〈110〉 directions, along with high-density low angle grain boundaries. Besides, both deformation twinning and dislocation multiplication were activated during tensile process, which acted as dominant deformation mechanisms. The findings above reveal that LPBF can fabricate high-quality CoCrNi MEAs with cellular and columnar sub-structures, and an excellent tensile strength without sacrificing ductility.