Effects of La on microstructure and mechanical properties of NbMoTiVSi0.2 refractory high entropy alloys

Abstract

To study the effects of La on the microstructure and mechanical properties of refractory high entropy alloys, NbMoTiVSi 0.2 alloys with different La contents were prepared. Phase constitution, microstructure evolution, compressive properties and related mechanisms were systematically studied. Results show that the alloys with La addition are composed of BCC solid solution, eutectic structure, MSi 2 disilicide phase and La-containing precipitates. Eutectic structure and most of La precipitates are formed at the grain boundaries. Disilicide phase is formed in the grains. La can change the grain morphologies from dendritic structure to near-equiaxed structure, and the average grain size decreases from 180 to 20 μm with the increase of La content from 0 to 0.5 at.%. Compressive testing shows that the ultimate strength and the yield strength increase with the increase of La content, which is resulted from the grain boundary strengthening. However, they cannot be greatly improved because of the formation of MSi 2 disilicide phase with low strength. The ductility decreases with the increase of La content, which is due to the La precipitates and brittle MSi 2 disilicide phase.