Activating multiple slip systems in the laves phase improves the high-temperature strength and elastic coordination of (TiZr)65-XNb15Mo20CrX alloy

Abstract

Introducing Laves phase into refractory multi-principal elements alloys (RMPEAs) is a new exploration direction to improve the alloy strength. In this work, we have prepared a series of (TiZr)65-XNb15Mo20CrX (x = 5,10,15,20) multi-principal elements alloys, by the addition of Cr to introduce the Laves phase for excellent high-temperature performance. The microstructure, phase constituents, and mechanical properties of the refractory high-entropy alloy were studied in the present work. Most of these alloys exhibited typical dendrite morphology, except for the alloy Cr5. Excessive Cr results in the formation of TiZr-enriched zones. In addition, twins can appear in as-cast alloys as a result of a significant lattice mismatch between the matrix and the Laves phase, which is caused by the rapid cooling process during melting. All alloys demonstrate remarkable strength when exposed to high temperatures, with compressive yields surpassing 552 MPa, peaking at 712 MPa at 800 °C, and compressive strains exceeding 30%. Benefiting from the Laves phase, the alloys do not show significant softening, making it possible for this alloy to work stably at 800 °C. Analyses of high-temperature specimens under different degrees of deformation reveal that small-sized Laves phases containing nano-twins precipitate in the matrix. The small-sized Laves phases and nano-twins restrict the movement of dislocations, leading to a large amount of dislocation accumulation, which improves the strength and plasticity of the alloy. Therefore, the current work on designing novel alloys provides new ideas for developing RMPEAs with synergistic strength and plasticity.