Role of Ti on the Microstructure and Mechanical Properties of MoNbTi Medium-Entropy Alloy

Equiatomic MoNb and MoNbTi alloys are synthesized by arc melting. Ti addition resulted in a significant grain refinement (from 115 μm to 34 μm) of MoNb alloy. Exposure to high temperature for considerably longer duration (24 h at 1673 K) did not alter the beneficial effect of grain refinement imparted by Ti addition. Also, addition of Ti (33 at. %) significantly reduces the overall density without effecting the hardness of MoNbTi alloy, which is one of the key findings of the present study (MoNb - 4.06 ± 0.01 GPa, MoNbTi - 4.10 ± 0.01 GPa). MoNbTi also showed an exceptionally high "density-normalized" hardness when compared to various high-entropy alloys of similar family. Finally, from a simple analysis it is found that extraordinarily high "density-normalized" hardness can be obtained in just two/three element equiatomic systems, suggesting that developing new concentrated alloy systems with more than 3 elements in equiatomic proportion may not be offering any benefits with respect to hardness (strength) in single phase material systems where the beneficial effect of solid solution strengthening is exhausted.