Elastic and mechanical properties of Nb(Cr, V)₂ C15 Laves phases

The effect of vanadium alloying additions to NbCr₂ has been studied, focusing on the phase stability, defect structures, elastic properties, and mechanical behavior of these C15 Laves phases. First, the ternary Nb-Cr-V phase diagram is presented. The C15 phase field of NbCr₂ is significantly extended by V alloying along the constant niobium isoplethal section, suggesting that V atoms substitute primarily on Cr sites rather than Nb sites. Next, the elastic properties of the CIS Nb(Cr, V)₂ Laves phases were examined using resonant ultrasound spectroscopy. The vanadium alloyed Laves phase alloys have slightly higher shear modulus values and lower Poisson's ratios than binary NbCr₂. Finally, the mechanical properties of the C15 phases were investigated by indentation tests at different temperatures. Increasing the vanadium content modestly increases the strength but slightly decreases the fracture toughness and increases the brittle-to-ductile transition temperature in the alloys. The correlations between the phase stability, defect structures, elastic properties, and mechanical response of the C15 phases are discussed using a combination of atomic size arguments and electronic structure analyses. From these interpretations, an alloying strategy for improving the mechanical properties in C15 NbCr₂ is proposed.