Designing Ternary Laves Phase-Based Eutectic Alloys CrFeNb_x with Excellent Strength, Toughness, and Thermal Stability

Three ternary Laves phase-based eutectic alloys CrFeNb_x (x = 2.0, 2.35, 2.7) were designed successfully by combining the binary phase diagrams and thermodynamics calculations. With the increasing Nb content, the solidified microstructures evolved from the primary (Cr, Fe)₂Nb plus the eutectic (Cr, Fe)₂Nb/Nbss in the CrFeNb_2.0, via the full eutectic (Cr, Fe)₂Nb/Nbss in the CrFeNb_2.35, and finally to the primary Nbss plus the eutectic (Cr, Fe)₂Nb/Nbss in the CrFeNb_2.7. The full eutectic (Cr, Fe)₂Nb/Nbss of the CrFeNb_2.35 was found with outstanding thermal stability, and the lamellar eutectic was quite stable even under the heat-treatment of 1273 K/48 h. The compression strength and fracture toughness increased firstly and decreased subsequently with the increase of Nb content, which reached their maximums of 2.54 GPa and 18.25 MPa·m^1/2, respectively, in the CrFeNb_2.35. The excellent combination of compression strength and fracture toughness in the CrFeNb_x (x = 2.0, 2.35, 2.7) were attributed to the synergistic effects of Laves phase strengthening, interface strengthening, solid solution strengthening, alloying toughening and Nbss phase toughening mechanisms.