NiNbTi(Al/Si) medium-entropy amorphous alloys with enhanced mechanical and thermal properties

Abstract

Medium-entropy amorphous alloys (MEAAs) have recently emerged as a distinct category of alloys, contributing significantly to both entropy effects and the development of metallic glasses. Despite the recognized importance of the entropy effect in MEAAs, its investigation in amorphous configurations has remained relatively unexplored. In this study, the thermal stability and mechanical properties of NiNbTi(Al/Si) MEAAs were tuned by adding 5 and 10 at% Al and Si. To systematically investigate the hardness, elastic modulus, thermal behavior and crystalization of NiNbTi(Al/Si) MEAAs, glassy alloys of five different compositions produced by the mechanical alloying method were studied. The results showed that (Ni₆₀Nb₂₀Ti₂₀)₉₀Si₁₀ exhibited higher thermal stability and better mechanical properties, while the addition of Al to Ni₆₀Nb₂₀Ti₂₀ alloy deteriorated both the thermal and mechanical properties. Crystallization of amorphous alloys, associated with the formation of intermetallic nanocrystals, significantly enhanced the mechanical properties. In (Ni₆₀Nb₂₀Ti₂₀)₉₀Si₁₀ glassy alloy, Si-contained intermetallics were formed after crystallization, which increased the hardness from 14.17 GPa to 22.95 GPa and the elastic modulus from 121.50 GPa to 238.34 GPa. The addition of 10 at% Si increased the onset temperature of crystallization of Ni₆₀Nb₂₀Ti₂₀ amorphous alloy from 605 to 616 °C, while the addition of 10 at% Al dramatically decreased the onset temperature of crystallization. The enhanced thermal stability and mechanical properties of Ni₆₀Nb₂₀Ti₂₀ alloy through Si addition are attributed to the formation of strong p-d hybrid covalent bonds that increase resistance to shear deformation.