Microstructure and Mechanical Properties of Dual‐Phase FeCoCrNiAl_0.6 High Entropy Alloys Prepared by Laser Directed Energy Deposition

Recently, dual‐phase high‐entropy alloys with excellent strength–ductility combination have attracted widespread attention in the scientific community. Herein, three dense and crack‐free dual‐phase FeCoCrNiAl_0.6 high entropy alloys (HEAs) were successfully prepared by laser directed energy deposition (LDED) via adjusting laser scanning speed. The alloys printed have formed fine columnar face‐centered cubic (FCC) dendrites and woven mesh body‐centered cubic (BCC) interdendrites. The BCC phase is further composed of nanoscale A2 and B2 phases formed by spinodal decomposition. As the laser scanning speed increased from 5 mm s⁻¹ to 9 mm s⁻¹, the fraction of FCC phase increased from 56.9 to 70.5%, and the size of FCC dendrites refined. The sample printed at 9 mm s⁻¹ with an average grain size of 3.9 μm showed a comprehensive mechanical property, namely, a high yield stress and ultimate tensile stress (712.0 and 1121.9 MPa) and a total elongation of 16.5%. The fracture surface changed from a cleavage‐type facet to ductile dimples as the laser scanning speed increased. Based on the microstructures of base materials, it can be concluded that the fine microstructure and soft FCC phase can prevent the initiation and propagation of microcracks and, thereafter, alleviate the brittle failure.