Microstructure and Mechanical Properties of Cr₂Nb-Based Laves Phase Alloys Prepared by Laser Surface Remelting

The microstructure and mechanical properties of Cr₂Nb-based intermetallic matrix composites fabricated by laser surface remelting were investigated at hypoeutectic and hypereutectic compositions. In the hypoeutectic composition, the molten zones under different laser scanning velocities consist of fully α-Cr dendrites, whereas a series of morphology evolutions perpendicular to the scanning direction occurred in the hypereutectic composition: Cr₂Nb primary phase + Cr/Cr₂Nb eutectic → Cr/Cr₂Nb eutectic → α-Cr primary phase + Cr/Cr₂Nb eutectic → fully α-Cr dendrite. Based on the maximum growth rate criterion, the microstructure evolutions of the molten zones were analyzed by considering the competitive growth among the α-Cr phase, Cr₂Nb Laves phase, and the Cr/Cr₂Nb eutectic, which are in agreement with the experimental results. More importantly, the room-temperature fracture toughness values of the hypoeutectic and hypereutectic alloys attain 11.2 MPa m^1/2 and 7.9 MPa m^1/2, respectively, which increase by eight and six times over the as-cast Cr₂Nb Laves phase (1.2 MPa m^1/2), respectively. The remarkable enhancements in room-temperature fracture toughness were explained in terms of fine-grain toughening, second Cr phase toughening, and point defects toughening.