Microstructure and mechanical properties of refractory high entropy (Mo0.5NbHf0.5ZrTi)BCC/M5Si3 in-situ compound

• In-situ (Mo0.5NbHf0.5ZrTi)BCC/M5Si3 compounds were prepared successfully.
• Mo0.5NbHf0.5ZrTiSix alloy has a BCC phase and M5Si3 phase.
• Microstructure evolves from hypoeutectic to hypereutectic with increasing Si.
• The addition of Si increases the hardness and strength.
• The yield strength and plasticity are improved for Si0.1 alloy.

Refractory high-entropy alloy Mo0.5NbHf0.5ZrTi is selected as the base alloy and element Si is added for preparing the (Mo0.5NbHf0.5ZrTi)BCC/M5Si3 in-situ compound. The effect of Si on the microstructure and mechanical properties of Mo0.5NbHf0.5ZrTi alloy is analyzed and discussed. The base alloy has the single body-centered cubic (BCC) phase. After adding Si, the alloy is composed of one BCC phase and the intermetallic M5Si3 phase with hexagonal close-packed (HCP) crystal structure. The microstructure gradually evolves from the hypoeutectic structure to eutectic structure and finally to hypereutectic structure with the increase of Si concentration. The addition of Si reduces the density and increases the hardness and strength of the base alloy due to the formation of M5Si3 phase. The plasticity of Si0.1 alloy is also improved due to the grain refinement and the weakening of the solution strengthening for the dominant BCC phase and the M5Si3 phase is fine while the plasticity decreases due to the formation of more brittle M5Si3 phase with a larger size as Si content increases.