Twinning deformation and toughening effect of Laves phase intermetallics

The Laves phases, with a topologically close-packed structure, exhibit superior high-temperature strength, slow self-diffusion rates, and excellent oxidation resistance, making them promising candidates for advanced high-temperature structural materials. However, the industrial application of this material is constrained by its pronounced room-temperature brittleness, which arises from the topologically closed structure. To enhance the room-temperature deformation capability of V 2 Hf Laves phases, this study investigates the effects of Nb alloying and the incorporation of a ductile secondary phase on V 2 Hf. This approach effectively regulates the stacking fault energy and refines the microstructure, thereby promoting twinning and enhancing ductility. The results indicate that the room-temperature fracture toughness of the as-cast Laves phase-based Hf 14 V 64 Nb 22 alloy achieves 8.87 MPa m 1/2 , which corresponds to a 640 % enhancement compared to the as-cast single-phase Laves phases with a toughness of 1.2 MPa m 1/2 . Additionally, the compressive elongation reaches an impressive 26.2 %. The presence of a ductile V(Nb) solid solution promotes twinning in V 2 Hf grains by facilitating crystal orientation adjustment. TEM analysis shows that twinning in the C15 V 2 Hf Laves phase occurs on the (111) plane with a [11-2] direction. The mechanism involves synchronous slip of the αcβ stacking sequence on (111), where atoms in the α layer remain fixed while β layer atoms displace by 1/6[11-2] into c layer positions. Simultaneously, the c layer shifts by 1/6[-211], causing a relative displacement of 1/6[-12-1] between the upper and lower crystals on the (111) plane, forming a Shockley partial dislocation.