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

Three ternary Laves phase-based eutectic alloys CrFeNbx (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 CrFeNb2.0, via the full eutectic (Cr, Fe)2Nb/Nbss in the CrFeNb2.35, and finally to the primary Nbss plus the eutectic (Cr, Fe)2Nb/Nbss in the CrFeNb2.7. The full eutectic (Cr, Fe)2Nb/Nbss of the CrFeNb2.35 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·m1/2, respectively, in the CrFeNb2.35. The excellent combination of compression strength and fracture toughness in the CrFeNbx (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.